Ivan's wiki https://yanevskiv.com/ 2026-06-06T19:06:12+00:00 Ivan's wiki https://yanevskiv.com/ https://yanevskiv.com/_media/logo.png text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) 115200 https://yanevskiv.com/115200?rev=1778758708&do=diff 115200 115200 is the default baud rate for Arduino USB-UART communication. picocom You specify the baudrate using -b option. $ picocom /dev/ttyACM0 -b 115200 To exit picocom, use Ctrl + A, X. This means holding control and pressing 'A' and 'X'. Don't release control while switching from 'A' to 'X'. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Arduino Uno R4 WiFi https://yanevskiv.com/arduino-uno-r4-wifi?rev=1778758708&do=diff Arduino Uno R4 WiFi Documentation: * <https://docs.arduino.cc/hardware/uno-r4-wifi/> text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/assert.h?rev=1778758708&do=diff <assert.h> In C programming language, <assert.h> is a header which is part of the C standard library. It provides assert(), which is used for runtime assertions. A runtime assertion is when you want to exit the program early because important condition isn't met. For example, you tried to allocate memory with text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of internal Bash shell commands https://yanevskiv.com/bash-internal?rev=1778758708&do=diff List of internal Bash shell commands text/html 2026-05-23T18:20:35+00:00 Anonymous (anonymous@undisclosed.example.com) Basis state https://yanevskiv.com/basis-state?rev=1779560435&do=diff Basis state Basis state is a state vector that is part of a basis. A basis is set of two or more quantum states out of which all other quantum states can be built through linear combination. A qubit is a two-level quantum system so has two basis states. The standard basis $\lvert 0\rangle, \lvert 1\rangle}$$\lvert\text{cat}\rangle$$\lvert\text{dog}\rangle$$d = 2$$\lvert\psi\rangle$$a,b\in\mathbb C$$\mathbb C^2$$\mathbb C^2$$$ \lvert\psi\rangle = \begin{pmatrix}a\\b\end{pmatrix},\quad\lvert\psi… text/html 2026-05-25T13:47:59+00:00 Anonymous (anonymous@undisclosed.example.com) Bell state https://yanevskiv.com/bell-state?rev=1779716879&do=diff Bell state Bell states are the four maximally entangled two-qubit states. They form an orthonormal basis for the two-qubit Hilbert space $\mathbb{C}^4$ and are named after physicist John Bell. Bell states play a central role in quantum teleportation, superdense coding, and quantum key distribution.$$\lvert\Phi^+\rangle = \frac{1}{\sqrt{2}}(\lvert 00\rangle + \lvert 11\rangle)$$$$\lvert\Phi^-\rangle = \frac{1}{\sqrt{2}}(\lvert 00\rangle - \lvert 11\rangle)$$$$\lvert\Psi^+\rangle = \frac{1}{\sqrt… text/html 2026-05-25T13:46:52+00:00 Anonymous (anonymous@undisclosed.example.com) Bloch sphere https://yanevskiv.com/bloch-sphere?rev=1779716812&do=diff Bloch sphere Bloch sphere is a geometrical representation of a single qubit state as a point on the surface of a unit sphere in three-dimensional space. It provides an intuitive way to visualize qubit states and the effect of quantum gates as rotations. The Bloch sphere is named after physicist Felix Bloch.$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$a, b \in \mathbb{C}$$|a|^2 + |b|^2 = 1$$\theta \in [0, \pi]$$\varphi \in [0, 2\pi)$$$\lvert\psi\rangle = \cos\frac{\theta}{2}\lvert 0… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Born rule https://yanevskiv.com/born-rule?rev=1778758708&do=diff Born rule Born rule is a postulate in quantum mechanics that gives an interpretation of probability amplitudes. Namely, probability amplitude $c\in\mathbb{C}$ associated with some state $\lvert i\rangle$ encodes the probability of finding the quantum system in the state $\lvert i\rangle$. The value of this probability $c$$$P_i = |c|^2$$$\lvert\psi\rangle$$a\in\mathbb{C}$$\lvert 0\rangle$$b\in\mathbb{C}$$\lvert 1\rangle$$$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$$\lvert 0\rangle$… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) C headers https://yanevskiv.com/c-headers?rev=1778758708&do=diff C headers C headers offer an interface to the C standard library. List of headers * <assert.h> * <complex.h> * <ctype.h> * <errno.h> * fenv.h * float.h * inttypes.h * iso646.h * limits.h * locale.h * math.h * setjmp.h * signal.h * stdalign.h * stdarg.h * stdatomic.h * stdbit.h * <stdbool.h> * stdckdint.h * stddef.h * stdint.h * stdio.h * stdlib.h * stdmchar.h * stdnoreturn.h * <string.h> * tgmath.h * thread.h * time.h * uchar.h * wchar.h * wctype.h Links * <… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) C standard library https://yanevskiv.com/c-standard-library?rev=1778758708&do=diff C standard library C standard library is one library that's always linked by default when you compile C programs. To use the library, a set of headers is offered which you can include by default. For example, <stdlib.h> and <stdio.h> in this code are headers from the C standard library (but there are also headers which are text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) CI/CD https://yanevskiv.com/ci-cd?rev=1778758708&do=diff CI/CD CI/CD stands for “continuous integration / continuous delivery”. It is a term used for a set of pratcies you put in place in order to simultaneously accomplish the following two: * Quickly integrate changes you make to your software into production ( text/html 2026-05-25T13:49:34+00:00 Anonymous (anonymous@undisclosed.example.com) CNOT gate https://yanevskiv.com/cnot-gate?rev=1779716974&do=diff CNOT gate CNOT gate (Controlled-NOT gate, also written CX) is a two-qubit quantum gate that flips the target qubit if and only if the control qubit is in state $\lvert 1\rangle$. It is one of the most fundamental and widely used gates in quantum computing. $$\text{CNOT} = \begin{pmatrix}1 & 0 & 0 & 0\\ 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 1\\ 0 & 0 & 1 & 0\end{pmatrix}$$ The rows and columns of this $4\times 4$$\lvert 00\rangle, \lvert 01\rangle, \lvert 10\rangle, \lvert 11\rangle$$$\text{CNOT}\lvert … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/complex.h?rev=1778758708&do=diff <complex.h> In C programming language, <complex.h> is a header which is part of the C standard library (specifically, C99). It implements the algebra of complex numbers $\mathbb C$. You need at least version C99 to use this header, so compile with gcc -std=c99 main.c -o program$2 + i3$$i$$z = 2 + i3$$|z|$$e^z$$\log(z)$$\sin(z)$$\cos(z)$$\tan(z)$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of coreutils commands https://yanevskiv.com/coreutils?rev=1778758708&do=diff List of coreutils commands coreutils (or GNU core utilities) are a set of commands inherited from Unix and implemented by the GNU project. These commands are pretty much available on all GNU/Linux systems, no matter the distro. The following is a table of coreutil commands. You can use text/html 2026-05-25T13:56:11+00:00 Anonymous (anonymous@undisclosed.example.com) $\mathbb{CP}^1$ https://yanevskiv.com/cp-1?rev=1779717371&do=diff $\mathbb{CP}^1$ Complex projective line (or $\mathbb{CP}^1$) is the Hilbert space where pure qubits live in. It is defined as the quotient space of $\mathbb{C}^2$ and $\mathbb{C}$, both of which are punctured in their respective zero elements. $$\mathbb{CP}^1 \stackrel{\text{def}}{=} (\mathbb{C}^2 \setminus\{0\})/\mathbb{C}^\times\qquad \mathbb{C}^\times\stackrel{\text{def}}{=}\mathbb{C} \setminus \{0\}$$ Motivation To do quantum computing, we usually use the Hilbert space $\mathbb{C}^2$$\lv… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/ctype.h?rev=1778758708&do=diff <ctype.h> In C programming language, <ctype.h> is a header which is part of the C standard library. It gives you functions related to the character type char. Although it does sound like it's something about C types (like short, int, float, double) rather than strictly about text/html 2026-05-25T13:55:47+00:00 Anonymous (anonymous@undisclosed.example.com) Density matrix https://yanevskiv.com/density-matrix?rev=1779717347&do=diff Density matrix Density matrix (written as $\rho$) is a matrix representation of a quantum state that is strictly more general than the state vector $\lvert\psi\rangle$. While a state vector can only represent pure states, a density matrix can represent mixed states as well, making it the correct tool for open quantum systems, noisy circuits, and statistical ensembles of quantum states.$\lvert\psi\rangle$$$\rho = \lvert\psi\rangle\langle\psi\rvert$$$\lvert 0\rangle$$\lvert 1\rangle$$$\rho_0 = \l… text/html 2026-05-25T13:50:36+00:00 Anonymous (anonymous@undisclosed.example.com) Deutsch-Jozsa algorithm https://yanevskiv.com/deutsch-jozsa?rev=1779717036&do=diff Deutsch-Jozsa algorithm Deutsch-Jozsa algorithm is a quantum algorithm that determines whether a function $f:\{0,1\}^n \to \{0,1\}$ is constant or balanced using exactly one quantum query. It was proposed by David Deutsch and Richard Jozsa in 1992 as a generalization of Deutsch's algorithm to $n$$f$$2^n$$2^{n-1} + 1$$n + 1$$n$$\lvert 0\rangle^{\otimes n}$$\lvert 1\rangle$$n+1$$n$$n$$$\lvert 0\rangle^{\otimes n}\lvert 1\rangle \xrightarrow{H^{\otimes n+1}} \frac{1}{\sqrt{2^n}}\sum_{x=0}^{2^n-1}\… text/html 2026-05-25T13:50:25+00:00 Anonymous (anonymous@undisclosed.example.com) Deutsch's algorithm https://yanevskiv.com/deutsch?rev=1779717025&do=diff Deutsch's algorithm Deutsch's algorithm is the simplest quantum algorithm that demonstrates a quantum speedup over any classical algorithm. It determines whether a binary function $f:\{0,1\} \to \{0,1\}$ is constant (same output for both inputs) or balanced (different outputs for the two inputs) using only a single quantum query, whereas any classical algorithm requires two.$f$$U_f$$\lvert x\rangle\lvert y\rangle \mapsto \lvert x\rangle\lvert y \oplus f(x)\rangle$$f$$f(0)$$f(1)$$U_f$$\lvert 0\r… text/html 2026-05-25T13:53:32+00:00 Anonymous (anonymous@undisclosed.example.com) Dirac notation https://yanevskiv.com/dirac-notation?rev=1779717212&do=diff Dirac notation Dirac notation (or bra-ket notation) is a convenient way to name vectors in a Hilbert space $\mathcal{H}$ (via “kets”) and its dual space $\mathcal{H}^*$ (via “bras”). Kets are written as $\lvert\text{name}\rangle$ and bras are written as $\langle\text{name}\rvert$. The text inside a bra or ket has no intrinsic meaning — it is simply a label, much like naming a variable in programming.$\lvert\psi\rangle$$\mathbb{C}^2$$a, b \in \mathbb{C}$$$\lvert\psi\rangle = \begin{pmatrix}a\\b\… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) do { ... } while (0) https://yanevskiv.com/do-while-0?rev=1778758708&do=diff do { ... } while (0) In C programming language,do { ... } while (0) is a loop which does a single iteration. A compiler will optimize it away completely, so the syntax produces no actual machine code. Most commonly, it's used to make function-macros. Example: /* * - clearing psr.i is implicitly serialized (visible by next insn) * - setting psr.i requires data serialization * - we need a stop-bit before reading PSR because we sometimes * write a floating-point register right before rea… text/html 2026-05-16T14:56:50+00:00 Anonymous (anonymous@undisclosed.example.com) docker https://yanevskiv.com/docker?rev=1778943410&do=diff docker What is docker? Docker is a tool for managing containers. Containers are somewhat like virtual machine instances except a lot more lightweight. Think of an application e.g. a web app. You want to run the application, but you don't want to pollute your host OS with all the baggage that comes with it (libraries, dependencies, config files, services, text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Eigenstate https://yanevskiv.com/eigenstate?rev=1778758708&do=diff Eigenstate Eigenstate is refers to a quantum state associated with a quantum gate that remains unchanged after applying the gate. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Embedded engineering glossary https://yanevskiv.com/embedded-glossary?rev=1778758708&do=diff Embedded engineering glossary * QNX (Quantum Network eXecutive) - A proprietary real-time operating system (RTOS) * Lock-free queue - An efficient MT-safe queue implemented only using atomic instructions with no spinlocks, semaphores or mutexes. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) EOF https://yanevskiv.com/eof?rev=1778758708&do=diff EOF EOF is an acronym that stands for “End of file” Shell In shell, EOF is commonly used as a terminator in what is called a heredoc (“here document”). It's when you want to supply a multiline text to a command to its standard output, using <<. $ cat > hello.txt << EOF Here, you can write anything you like. It's not over until you actually type E-O-F. You can cancel with Ctrl + C. EOF text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) (WIP) Equations of Electromagnetism https://yanevskiv.com/eqn-electromagnetism?rev=1778758708&do=diff (WIP) Equations of Electromagnetism Electrostatics Coulomb's law Attractive force $Q_2$ feels thanks to $Q_1$'s electric field: $$\mathbf F_ = \frac{1}{4\pi\varepsilon_0}\frac{Q_1Q_2}{r^2}\mathbf r_{012}$$ Electric field Electric field created by a single point charge $Q$: $$\mathbf E = \frac{1}{4\pi\varepsilon_0}\frac{Q}{r^2}\mathbf r_0$$ Electric field created by multiple point charges $Q_1, Q_2, ..., Q_N$: $$\mathbf E = \frac{1}{4\pi\varepsilon_0}\sum_{i=1}^{N}\frac{Q_i}{r^2_i}\mathbf r… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/errno.h?rev=1778758708&do=diff <errno.h> In C programming language, <errno.h> is a header that's part of the C standard library. It defines all the ENAME constants used to name errors and gives access to the global int errno;. Constants Standard POSIX errors: E2BIG EACCES EADDRINUSE EADDRNOTAVAIL EAFNOSUPPORT EAGAIN EALREADY EBADF EBADMSG EBUSY ECANCELED ECHILD ECONNABORTED ECONNREFUSED ECONNRESET EDEADLK … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Exit status https://yanevskiv.com/exit-status?rev=1778758708&do=diff Exit status Exit status lets the user of your program know if the program ended in success or failure. Commonly, 0 is success, any other value is failure (most commonly, failure is 1 -- a bit counter intuitive at first!) Your users can inspect it with text/html 2026-05-14T13:24:19+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/fdsa?rev=1778765059&do=diff fdsafdsafdsafdas fdsafdsafds text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) FFT https://yanevskiv.com/fft?rev=1778758708&do=diff FFT FFT (or Fast Fourier Transform) is an algorithm that computes DFT (or “Discrete Fourier Transform”). There are several FFT algorithms but the most popular one is called Cooley–Tukey FFT. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Function macro https://yanevskiv.com/function-macro?rev=1778758708&do=diff Function macro Function macro is a C preprocessor macro that looks like a function call when you use it. This is a basic example with a single expression. sqr(x) looks and feels like a function even though it's a macro. A good habit to get into is to always enclose arguments into parenthesis when you define function macros. For example, text/html 2026-05-25T13:48:25+00:00 Anonymous (anonymous@undisclosed.example.com) GHZ state https://yanevskiv.com/ghz-state?rev=1779716905&do=diff GHZ state GHZ state (Greenberger-Horne-Zeilinger state) is a maximally entangled quantum state of three or more qubits. The three-qubit GHZ state is an equal superposition of all-zeros and all-ones. $$\lvert\text{GHZ}\rangle = \frac{1}{\sqrt{2}}(\lvert 000\rangle + \lvert 111\rangle)$$ The GHZ state is named after Daniel Greenberger, Michael Horne, and Anton Zeilinger, who introduced it in 1989. It is a natural generalization of the two-qubit Bell state $\lvert\Phi^+\rangle$$0$$1$$n$$n \geq 2… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Docker (Reference) https://yanevskiv.com/gist-docker?rev=1778758708&do=diff Docker (Reference) This page includes a myriad docker commands for reference. Basic Containers Run ubuntu:latest image (will do docker pull automatically if you don't have it) docker run -it --rm ubuntu:latest Images Pull ubuntu:latest image text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Git (Examples) https://yanevskiv.com/gist-git?rev=1778758708&do=diff Git (Examples) Basics Creating a repository with an initial commit: git init Adding a file to the staging area: git add file.txt Un-adding a file from the staging area: git restore --staged file.txt Showing what's in the staging area: text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) (WIP) Semaphores (Examples) https://yanevskiv.com/gist-semaphores?rev=1778758708&do=diff (WIP) Semaphores (Examples) This page includes some examples of semaphores in multi-threading environments. The syntax is borrowed from EasyMT. Basic Synchronization Two threads a() and b() alternate their execution regardless of the scheduler. Output: $B$$B$ text/html 2026-05-16T14:56:33+00:00 Anonymous (anonymous@undisclosed.example.com) git https://yanevskiv.com/git?rev=1778943393&do=diff git Git is a tool for managing repositories. Repositories are like folders, except it's easier to track the changes that happen inside them. Think of a project you've been working on e.g. a game in written in C++. You've been working on your game for weeks and now you have quite a bit of code. You're starting to be a little afraid of making changes text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) .gitignore https://yanevskiv.com/gitignore?rev=1778758708&do=diff .gitignore .gitignore is a file You can ignore everything in a given di F.A.Q. How do I ignore a directory without making a commit? Just put * in .gitignore of the directory you want to ignore (e.g. ./local directory) # ./local/.gitignore # Ignore everything in directory `./local` * text/html 2026-05-25T13:54:01+00:00 Anonymous (anonymous@undisclosed.example.com) Global phase https://yanevskiv.com/global-phase?rev=1779717241&do=diff Global phase Global phase is a property of a quantum state that emerges from the mathematical description but is physically completely unobservable. Multiplying an entire quantum state by a complex number of unit magnitude $e^{i\phi}$ produces a state that is physically identical to the original in every possible measurement.$a = Ae^{i\alpha}$$b = Be^{i\beta}$$A, B \in \mathbb{R}$$\alpha, \beta \in (-\pi, \pi]$$$\lvert\psi\rangle = Ae^{i\alpha}\lvert 0\rangle + Be^{i\beta}\lvert 1\rangle$$$\lve… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) GNU/Linux https://yanevskiv.com/gnu-linux?rev=1778758708&do=diff GNU/Linux GNU/Linux is a free operating system that replaced the older operating system called Unix. It's ubiquitous on servers and supercomputers. It's an increasingly popular choice for desktops, but not yet common. It's also the operating system behind SteamOS. text/html 2026-05-25T13:51:09+00:00 Anonymous (anonymous@undisclosed.example.com) Grover's algorithm https://yanevskiv.com/grover?rev=1779717069&do=diff Grover's algorithm Grover's algorithm is a quantum search algorithm that finds a marked element in an unstructured database of $N$ items in $O(\sqrt{N})$ queries. It was invented by Lov Grover in 1996 and provides a quadratic speedup over classical brute-force search, which requires $O(N)$$U_f$$\lvert x^*\rangle$$U_f\lvert x\rangle = -\lvert x\rangle$$x = x^*$$U_f\lvert x\rangle = \lvert x\rangle$$\lvert s\rangle = H^{\otimes n}\lvert 0\rangle^{\otimes n}$$\lvert x^*\rangle$$G$$U_f$$D = 2\lvert… text/html 2026-05-25T13:49:05+00:00 Anonymous (anonymous@undisclosed.example.com) Hadamard gate https://yanevskiv.com/h-gate?rev=1779716945&do=diff Hadamard gate Hadamard gate (or H gate) is one of the most important single-qubit quantum gates. It maps the computational basis states $\lvert 0\rangle$ and $\lvert 1\rangle$ to equal superpositions, and is used at the start of most quantum algorithms to create superposition from a classical input.$$H = \frac{1}{\sqrt{2}}\begin{pmatrix}1 & 1\\ 1 & -1\end{pmatrix}$$$\lvert +\rangle$$\lvert -\rangle$$$H\lvert 0\rangle = \frac{\lvert 0\rangle + \lvert 1\rangle}{\sqrt{2}} = \lvert +\rangle$$$$H\lv… text/html 2026-05-16T17:56:22+00:00 Anonymous (anonymous@undisclosed.example.com) Harvard architecture https://yanevskiv.com/harvard-architecture?rev=1778954182&do=diff Harvard architecture Harvard archictecture is a type of computer archictecture. It's a type of architecture where code and data are kept in separate memories. The Harvard architecture can be contrasted against von-Neumann archictecture. In the latter, code and data are both stored in the same working memory (RAM). The CPU has to fetch both the instructions and data by accessing the same memory bus, leading to what is known as von-Neumann bottleneck. This doesn't really matter, of course text/html 2026-05-14T13:01:33+00:00 Anonymous (anonymous@undisclosed.example.com) Header guard https://yanevskiv.com/header-guard?rev=1778763693&do=diff Header guard Header guards are a pattern used in C and C++ programming languages when writing header files. Header files (.h files) are files that are included in source files (.c and .cpp files) near the top (hence the name) using the #include <...>_ text/html 2026-05-25T13:51:47+00:00 Anonymous (anonymous@undisclosed.example.com) HHL algorithm https://yanevskiv.com/hhl?rev=1779717107&do=diff HHL algorithm HHL algorithm (Harrow-Hassidim-Lloyd algorithm) is a quantum algorithm for solving systems of linear equations $Ax = b$ where $A$ is an $N\times N$ sparse Hermitian matrix. Proposed in 2009, it achieves an exponential speedup over classical linear solvers under certain conditions.$O(Ns\kappa\log(1/\varepsilon))$$s$$\kappa$$\varepsilon$$O(\log(N)s^2\kappa^2/\varepsilon)$$N$$\lvert b\rangle$$A$$\lambda_j$$A$$\lvert\lambda_j\rangle \mapsto (C/\lambda_j)\lvert\lambda_j\rangle$$A^{-1}$… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Hilbert space https://yanevskiv.com/hilbert-space?rev=1778758708&do=diff Hilbert space Hilbert space is a complete inner product space. It is vector space that is equipped with an inner product such that the metric induced by the inner product is complete within the space. Completeness means that all Cauchy sequences converge within the same space. Hilbert space is a special case of the more general Banach space, both of which are concepts from functional analysis.$\mathbb{R}$$\mathbb{C}$$\lvert\psi\rangle$ text/html 2026-05-25T13:08:35+00:00 Anonymous (anonymous@undisclosed.example.com) Home https://yanevskiv.com/home?rev=1779714515&do=diff Home Hi, I'm Ivan! This website is my encyclopedia about various technical topics. The topics I cover on this wiki are mostly related to technology, but sometimes I also write about mathematics and physics. I'm an embedded software engineer. Therefore, most of the articles on this website are going to be written from that lens. For example, if I make an analogy, it's probably going to be related to embedded engineering in some way. I use text/html 2026-05-25T13:56:27+00:00 Anonymous (anonymous@undisclosed.example.com) Hopf fibration https://yanevskiv.com/hopf-fibration?rev=1779717387&do=diff Hopf fibration Hopf fibration is a map connecting the state vector representation of a qubit $\lvert\psi\rangle \in \mathbb{C}^2$ to a point on the Bloch sphere $(x, y, z) \in \mathbb{R}^3$. It explains why a qubit — an object living in the complex space $\mathbb{C}^2$ — can be visualized as a point on a real three-dimensional sphere.$a, b \in \mathbb{C}$$|a|^2 + |b|^2 = 1$$\mathbb{C}^2$$S^3$$S^3/U(1) \cong S^2$$\pi: S^3 \to S^2$$S^2$$S^3$$U(1)$$\pi$$\sigma_x, \sigma_y, \sigma_z$$$\pi:\mathbb{C… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) HPC https://yanevskiv.com/hpc?rev=1778758708&do=diff HPC HPC (High-performance computing) is an area of programming concerned with performance optimization. It's about making the most out of hardware. text/html 2026-05-25T13:51:34+00:00 Anonymous (anonymous@undisclosed.example.com) Hidden subgroup problem https://yanevskiv.com/hsp?rev=1779717094&do=diff Hidden subgroup problem Hidden subgroup problem (HSP) is a class of problems that provides a unified framework for many quantum algorithms. The problem is: given a group $G$, a set $X$, and a function $f: G \to X$ that is constant on cosets of some subgroup $H \leq G$ and takes distinct values on different cosets, find the hidden subgroup $H$$\mathbb{Z}_2$$\mathbb{Z}_2^n$$\mathbb{Z}$$\mathbb{Z}_N$$G$$G$$\frac{1}{\sqrt{|H|}}\sum_{h\in H}\lvert x_0 h\rangle$$x_0$$G$$G$$H$$O(\log|G|)$$H$$G$$S_n$$D… text/html 2026-05-25T10:15:14+00:00 Anonymous (anonymous@undisclosed.example.com) I gate https://yanevskiv.com/i-gate?rev=1779704114&do=diff I gate I gate (or Identity gate) is a quantum gate that leaves the state vector unchanged. In other words, it does nothing. It's commonly drawn as a wire. Its matrix representation is equivalent to the identity matrix. For a single qubit, the Identity gate is represented by a $$I = \begin{pmatrix}1 & 0\\ 0 & 1\end{pmatrix}$$$I$$\lvert\psi\rangle$$I\lvert\psi\rangle$$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$$I\lvert\psi\rangle = \begin{pmatrix}1 & 0\\ 0 & 1\end{pmatrix}\begin{pma… text/html 2026-05-25T13:47:33+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert i\rangle$ https://yanevskiv.com/i-state?rev=1779716853&do=diff $\lvert i\rangle$ Plus-i state $\lvert i\rangle$ (also written $\lvert +i\rangle$ or $\lvert y\rangle$) is a quantum state that is an equal superposition of $\lvert 0\rangle$ and $\lvert 1\rangle$ with a relative phase of $+i$. It is one of the six cardinal states on the Bloch sphere, sitting at the positive $y$-axis with coordinates $(0, 1, 0)$. $$\lvert i\rangle = \frac{1}{\sqrt{2}}\lvert 0\rangle + \frac{i}{\sqrt{2}}\lvert 1\rangle = \frac{1}{\sqrt{2}}\begin{pmatrix}1\\i\end{pmatrix}$$ It … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) ifupdown https://yanevskiv.com/ifupdown?rev=1778758708&do=diff ifupdown ifupdown is the traditional network manager on GNU/Linux systems. It has since been replaced by systemd-networkd. It was especially commmon in Debian systems before Debian 12 (Bookworm). The “if” part is short for “interface”. “up” and “down” refer to text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Introduction to quantum computing https://yanevskiv.com/introduction-to-quantum-computing?rev=1778758708&do=diff Introduction to quantum computing Quantum computing is a theory of programming a quantum computer. If you're reading this article, you're likely curious about quantum computing and would like to learn more. How does a quantum computer work? What makes it different from a classical computer? How exactly do you program it? If you don't have a background in physics quantum computing may initially seem math-heavy and rather difficult to understand. An assumption I'm going to make is that the reade… text/html 2026-05-25T13:50:01+00:00 Anonymous (anonymous@undisclosed.example.com) iSWAP gate https://yanevskiv.com/iswap-gate?rev=1779717001&do=diff iSWAP gate iSWAP gate is a two-qubit quantum gate that swaps the states of two qubits and simultaneously multiplies the swapped states by the imaginary unit $i$. $$\text{iSWAP} = \begin{pmatrix}1 & 0 & 0 & 0\\ 0 & 0 & i & 0\\ 0 & i & 0 & 0\\ 0 & 0 & 0 & 1\end{pmatrix}$$ The gate maps $\lvert 01\rangle \mapsto i\lvert 10\rangle$ and $\lvert 10\rangle \mapsto i\lvert 01\rangle$, while leaving $\lvert 00\rangle$ and $\lvert 11\rangle$ unchanged. The extra factor of $i$ distinguishes it from the … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) KDP Midterm (2026-01-10) Question 1 https://yanevskiv.com/kdp20260110-1?rev=1778758708&do=diff KDP Midterm (2026-01-10) Question 1 Write and explain the Fine grain ticket algorithm implemented with $\text{FA}$ opeartion. If we replaced $\text{FA}$ with $\text{TS}$ (test-and-set) operation implemented in the following way, would it be possible to implement a fine-grained solution? If yes, implement it. Is the critical section entry fair? Why / why not?$\text{FA}$$\text{TS}$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) KDP Midterm (2026-01-10) Question 2 https://yanevskiv.com/kdp20260110-2?rev=1778758708&do=diff KDP Midterm (2026-01-10) Question 2 Consider a dining table that can seat at most $N$ people ($N > 2$). A person may take some food, sit at the table (sitAtTable()), eat, leave the table (leaveTable()) and walk away. No person should eat alone i.e. sit at the table alone. Also, every person that takes food must necessarily sit down in order to eat. Create a solution for this probalom using a text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) KDP Exam (2026-02-18) Question 1 https://yanevskiv.com/kdp20260218-1?rev=1778758708&do=diff KDP Exam (2026-02-18) Question 1 Solve the dining philsophers problem by using signal and continue monitor discipline and by using covering condition technique. Ensure philosphers start eating in the order of their arrival. Solution #define N 5 /* number of philosophers */ monitor DiningPhilosophers { enum { THINKING, HUNGRY, EATING }; int phil[N]; cond delay[N]; queue<int> q; bool canEat(int id) { return (phil[(id - 1 + N) % N] != EATING) && (phil[(id + 1)… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) KDP Exam (2026-02-18) Question 2 https://yanevskiv.com/kdp20260218-2?rev=1778758708&do=diff KDP Exam (2026-02-18) Question 2 The Roller Coaster Problem. Assume there are $N$ passengers and $M$ cars in one roller coaster. Passengers alternate between walking around the amusement park and riding the roller coaster. One car can take at most $K$ passengers where $K < N$$K$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) (WIP) KDP Exam (2026-02-18) Question 3 https://yanevskiv.com/kdp20260218-3?rev=1778758708&do=diff (WIP) KDP Exam (2026-02-18) Question 3 Using synchronous message passing (synch_send, receive) write a distributed solution for The Dining Philosophers problem. In the distributed solution philosopher processes may only communicate with corresponding fork processes and fork processes may only communicate with corresponding philosopher processes. text/html 2026-05-17T15:33:19+00:00 Anonymous (anonymous@undisclosed.example.com) kpsewhich https://yanevskiv.com/kpsewhich?rev=1779031999&do=diff kpsewhich kpsewhich is a LaTeX-related command. It's a diagnostic command that's used to look up the full path of a file you know the LaTeX compiler would use implicitly. In some way, it is similar to the which command, which shows the full path of a command if you would run it in the shell (e.g. text/html 2026-05-25T13:55:58+00:00 Anonymous (anonymous@undisclosed.example.com) Kraus operator https://yanevskiv.com/kraus-operator?rev=1779717358&do=diff Kraus operator Kraus operators $\{K_k\}$ are a set of matrices used to represent a quantum channel — a completely positive trace-preserving (CPTP) map $\mathcal{E}$ that sends density matrices to density matrices. Any physically valid quantum channel can be expressed in Kraus form.$$\mathcal{E}(\rho) = \sum_k K_k\rho K_k^\dagger$$$\sum_k K_k^\dagger K_k = I$$\text{tr}(\mathcal{E}(\rho)) = \text{tr}(\rho) = 1$$p$$K_0 = \sqrt{1-p}\,I$$K_1 = \sqrt{p}\,X$$p$$K_0 = \sqrt{1-p}\,I$$K_1 = \sqrt{p/3}\,X… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Landauer's principle https://yanevskiv.com/landauers-principle?rev=1778758708&do=diff Landauer's principle Landauer's principle establishes the thermodynamic lower bound on energy required to erase information from a physical system (e.g. a computer register). At temperature $T$, the minimum energy needed to erase information is: $$E = (\text{bits erased}) \times k_B T \ln 2$$ Where $k_B$ is the Boltzman's constant.$S_0 = 64\times k_B\ln 2$$S_1 = 0$$\Delta S = S_0 - S_1$$Q = T \Delta S$$T = 300K$$$ E_\text{bit} \approx 2.9\times 10^{-21} J$$$$ E_\text{bit} \approx 0.018 \text… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) LaTeX syntax https://yanevskiv.com/latex-syntax?rev=1778758708&do=diff LaTeX syntax For addition, you use the + symbol e.g. a + b = c: $$ a + b = c$$ For subtraction, you use the - symbol e.g. a - b = c $$ a - b = c$$ For multiplication, you just write ab or put a dot in between with \cdot (meaning: “centered dot”) like a \cdot b. Using a * b$a * b$$$a\cdot b = c$$$a / b$$${a \over b} = c$$$$ a = b \pmod{N}$$$$e^{i\phi} = \cos(\phi) + i\sin(\phi)$$$$\ln(1 + x) = 1 + x + $$$$\int \iint \iiint \oint \oiint \oiiint$$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) LaTeX https://yanevskiv.com/latex?rev=1778758708&do=diff LaTeX Latex (stylized as $\LaTeX$) is a markup language used to create scientific papers. It's the language used to produce PDF documents, like the ones you'll commonly see on arXiv. Latex has a simple declarative syntax that looks like \command[opt1][opt2]...[optN]{arg1}{arg2}...{argN} text/html 2026-05-25T13:52:39+00:00 Anonymous (anonymous@undisclosed.example.com) Lindblad master equation https://yanevskiv.com/lindbald-equation?rev=1779717159&do=diff Lindblad master equation Lindblad master equation (also called the GKSL equation, after Gorini, Kossakowski, Sudarshan, and Lindblad) is the most general Markovian master equation for the time evolution of the density matrix $\rho$ of an open quantum system — one that interacts with its environment.$$\frac{d\rho}{dt} = -\frac{i}{\hbar}[H, \rho] + \sum_k\left(L_k\rho L_k^\dagger - \frac{1}{2}L_k^\dagger L_k\rho - \frac{1}{2}\rho L_k^\dagger L_k\right)$$$-i[H,\rho]/\hbar$$L_k$$L_k$$\lvert 1\rangl… text/html 2026-05-22T23:40:25+00:00 Anonymous (anonymous@undisclosed.example.com) Lindbald master equation https://yanevskiv.com/lindbald-master-equation?rev=1779493225&do=diff Lindbald master equation Lindbald master equation is the equation that generalizes the Schrodinger equation. The following is the equation written in terms of density matrix $\rho$. $$\frac{d\rho}{dt} = -\frac{i}{\hbar}[H, \rho] + \sum_k\left(L_k^\dagger L_k - \frac{1}{2}\{L_k^\dagger L_k, \rho\}\right)$$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of algorithms https://yanevskiv.com/list-of-algorithms?rev=1778758708&do=diff List of algorithms * selection-sort * bubble-sort * insert-sort * merge-sort * quick-sort * 3d-rotation text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of C concepts https://yanevskiv.com/list-of-c-concepts?rev=1778758708&do=diff List of C concepts * C standard library * #pragma once * do { ... } while (0) * Function macro * main() return * Exit status * Header guard * Embedded engineering glossary text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of C headers https://yanevskiv.com/list-of-c-headers?rev=1778758708&do=diff List of C headers * <assert.h> * <complex.h> * <ctype.h> * <errno.h> * fenv.h * float.h * inttypes.h * iso646.h * limits.h * locale.h * math.h * setjmp.h * signal.h * stdalign.h * stdarg.h * stdatomic.h * stdbit.h * <stdbool.h> * stdckdint.h * stddef.h * stdint.h * stdio.h * stdlib.h * stdmchar.h * stdnoreturn.h * <string.h> * tgmath.h * thread.h * time.h * uchar.h * wchar.h * wctype.h * curses.h * getopt.h text/html 2026-05-18T12:47:30+00:00 Anonymous (anonymous@undisclosed.example.com) List of commands https://yanevskiv.com/list-of-commands?rev=1779108450&do=diff List of commands * List of util-linux commands * List of LaTeX commands * List of system commands * list-of-coreutils-commands * list-of-bash-internal-commands * List of HPC commands text/html 2026-05-23T00:05:17+00:00 Anonymous (anonymous@undisclosed.example.com) List of concepts in quantum control https://yanevskiv.com/list-of-concepts-in-quantum-control?rev=1779494717&do=diff List of concepts in quantum control * List of optimal quantum control algorithms * list-of-hamiltonians * pulse-shaping * drag-pulse * rabi-cycle * spin-echo * optimal-pulse-control * rotating-wave-approximation text/html 2026-05-23T00:00:03+00:00 Anonymous (anonymous@undisclosed.example.com) List of concepts in quantum error correction https://yanevskiv.com/list-of-concepts-in-quantum-error-correction?rev=1779494403&do=diff List of concepts in quantum error correction * List of quantum error correction codes * list-of-lindbald-operators * list-of-kraus-operators * Density matrix * Lindbald master equation * Kraus operator * lindbald-operator * list-of-lindbald-operators * quantum-channel * cptp-map * superoperator * fault-tolerance text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of concepts https://yanevskiv.com/list-of-concepts?rev=1778758708&do=diff List of concepts * C * header-guards * #pragma once * C++ * Name mangling * Rule of 5 * Miscellaneous * Numbers every programmer should know text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of C++ concepts https://yanevskiv.com/list-of-cpp-concepts?rev=1778758708&do=diff List of C++ concepts * Name mangling * Rule of 5 * CRTP * constexpr text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of C++ headers https://yanevskiv.com/list-of-cpp-headers?rev=1778758708&do=diff List of C++ headers * opencv.hpp * imgui.h * catch2.hpp * doctest.hpp text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of data structures https://yanevskiv.com/list-of-data-structures?rev=1778758708&do=diff List of data structures * array * forward-list * linked-list * dynamic-array * stack * queue * circular-buffer * matrix * binary-tree * heap * red-black-tree * b-tree * b-plus-tree * hash-map * graph text/html 2026-05-16T17:56:50+00:00 Anonymous (anonymous@undisclosed.example.com) List of embedded engineering concepts https://yanevskiv.com/list-of-embedded-engineering-concepts?rev=1778954210&do=diff List of embedded engineering concepts * List of logic gates * rtos * xv6 * riscv * x86-64 * mcu * spi * uart * i2c * gpio * wcet * Harvard architecture text/html 2026-05-23T00:08:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of essential quantum computing concepts https://yanevskiv.com/list-of-essential-quantum-computing-concepts?rev=1779494908&do=diff List of essential quantum computing concepts * List of quantum gates * List of quantum states * List of quantum algorithms * Qubit * Two qubits * Quantum register * Quantum gate * Born rule * quantum-state * State vector * Pauli gate * Global phase * Basis state * Eigenstate * relative-phase * clifford-gate * Hopf fibration * $\mathbb{CP}^1$ * unitary-gate * quantum-measurement * Bloch sphere * Dirac notation * dagger-operation * matrix-transpose * complex-conjugate * … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of hardware https://yanevskiv.com/list-of-hardware?rev=1778758708&do=diff List of hardware * ThinkPad * Arduino Uno R4 WiFi * weller-we-1010 text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of headers in C++ https://yanevskiv.com/list-of-headers-cpp?rev=1778758708&do=diff List of headers in C++ <https://en.cppreference.com/w/cpp/headers.html> text/html 2026-05-18T12:47:53+00:00 Anonymous (anonymous@undisclosed.example.com) List of HPC commands https://yanevskiv.com/list-of-hpc-commands?rev=1779108473&do=diff List of HPC commands * nvcc * cuobjdump text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of KDP exercises https://yanevskiv.com/list-of-kdp-exercises?rev=1778758708&do=diff List of KDP exercises * KDP Midterm (2026-01-10) Question 1 * KDP Midterm (2026-01-10) Question 2 * KDP Exam (2026-02-18) Question 1 * KDP Exam (2026-02-18) Question 2 * (WIP) KDP Exam (2026-02-18) Question 3 * kdp20260218-4 text/html 2026-05-17T15:16:35+00:00 Anonymous (anonymous@undisclosed.example.com) List of LaTeX commands https://yanevskiv.com/list-of-latex-commands?rev=1779030995&do=diff List of LaTeX commands * pdflatex * kpsewhich text/html 2026-05-16T14:58:56+00:00 Anonymous (anonymous@undisclosed.example.com) List of logic gates https://yanevskiv.com/list-of-logic-gates?rev=1778943536&do=diff List of logic gates * and-gate * or-gate * not-gate * nand-gate * nor-gate text/html 2026-05-23T00:11:37+00:00 Anonymous (anonymous@undisclosed.example.com) List of miscellaneous quantum computing concepts https://yanevskiv.com/list-of-miscellaneous-quantum-computing-concepts?rev=1779495097&do=diff List of miscellaneous quantum computing concepts * schrodinger-picture * heisenberg-picture * interaction-picture * measurement-problem * intepretation-of-quantum-mechanics * copenhagen-interpretation * many-world-interpretation text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of miscellaneous topics https://yanevskiv.com/list-of-miscellaneous-topics?rev=1778758708&do=diff List of miscellaneous topics * bytebeat * code-golf * List of KDP exercises text/html 2026-05-22T23:05:24+00:00 Anonymous (anonymous@undisclosed.example.com) List of optimal quantum control algorithms https://yanevskiv.com/list-of-optimal-quantum-control-algorithms?rev=1779491124&do=diff List of optimal quantum control algorithms * grape * crab * goat text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of parallel computing concepts https://yanevskiv.com/list-of-parallel-computing-concepts?rev=1778758708&do=diff List of parallel computing concepts * introduction-to-parallel-computing * synchronization-primitve * SAXPY * Semaphore * mutex * Numbers every programmer should know * amdahls-law * gustafsons-law * cache-coherence * cuda * openmp * queuing-theory * lock-free-queue * numa * false-sharing * aba-problem * trace-monoid * hazard-pointer * cache-coherence * roofline-model * numa * embarrassingly-parallel * fork-join-model * rcu * lock * lock-convoy * lock-contention * sp… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of paths https://yanevskiv.com/list-of-paths?rev=1778758708&do=diff List of paths * /bin * /dev * /boot * /etc * /home * /lib * /mnt * /opt * /proc * /root * /sbin * /srv * /tmp * /usr * /var text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum algorithms https://yanevskiv.com/list-of-quantum-algorithms?rev=1778758708&do=diff List of quantum algorithms * Quantum Fourier transform * Quantum phase estimation * Shor's algorithm * Grover's algorithm * Deutsch-Jozsa algorithm * QAOA * VQE text/html 2026-05-25T13:57:20+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum computing concepts https://yanevskiv.com/list-of-quantum-computing-concepts?rev=1779717440&do=diff List of quantum computing concepts * Qubit * Born rule * Dirac notation * Global phase * $\mathbb{CP}^1$ * Hopf fibration * Bloch sphere * Pure state * Mixed state * $\lvert 0\rangle$ * $\lvert 1\rangle$ * $\lvert +\rangle$ * $\lvert -\rangle$ * $\lvert i\rangle$ * $\lvert -i\rangle$ * Two qubits * Bell state * Three qubits * W state * GHZ state * NOON state * Quantum register * Quantum gate * Multiqubit gates * I gate * X-gate * Y gate * Z gate * Rotation gates * … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum computing libraries https://yanevskiv.com/list-of-quantum-computing-libraries?rev=1778758708&do=diff List of quantum computing libraries * qiskit * q-sharp text/html 2026-05-22T23:51:27+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum error correction codes https://yanevskiv.com/list-of-quantum-error-correction-codes?rev=1779493887&do=diff List of quantum error correction codes * repetition-code * shor-code * surface-code text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum gates https://yanevskiv.com/list-of-quantum-gates?rev=1778758708&do=diff List of quantum gates * I gate * X-gate * Y gate * Z gate * Rotation gates * s-gate * t-gate * Hadamard gate * Phase gate * U gate * ccnot-gate * CNOT gate * SWAP gate * iSWAP gate text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of quantum states https://yanevskiv.com/list-of-quantum-states?rev=1778758708&do=diff List of quantum states * $\lvert 0\rangle$ * $\lvert 1\rangle$ * $\lvert +\rangle$ * $\lvert -\rangle$ * plus-i-state * $\lvert -i\rangle$ * Bell state * W state * GHZ state text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of software engineering concepts https://yanevskiv.com/list-of-software-engineering-concepts?rev=1778758708&do=diff List of software engineering concepts * brooks-law * parkinsons-law * kanban * xp-programming * agile * Test-driven development * CI/CD * devops * blue-green-deployment * canary-release * unit-test * regression * test-automation * kanban * feature-flag * production * ab-testing * hotfix * feature-branch * eat-your-own-dog-food * spike-solution * solid * liskov-substitution-principle * smart-and-vapid * devops * incremental-build-model * prototype * artifact * goodha… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of software engineering tools https://yanevskiv.com/list-of-software-engineering-tools?rev=1778758708&do=diff List of software engineering tools * jira * confluence * ms-teams * harvestapp * notion text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of syntaxes https://yanevskiv.com/list-of-syntaxes?rev=1778758708&do=diff List of syntaxes * c-syntax * cpp-syntax * LaTeX syntax text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of system commands https://yanevskiv.com/list-of-system-commands?rev=1778758708&do=diff List of system commands * ifupdown text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of tools https://yanevskiv.com/list-of-tools?rev=1778758708&do=diff List of tools * git * docker * Terminal * Shell * LaTeX * tmux * ssh * VPS * qemu * gcc * gdb * nvim * perf text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) List of util-linux commands https://yanevskiv.com/list-of-util-linux-commands?rev=1778758708&do=diff List of util-linux commands util-linux is a collection of commands provided by the Linux Kernel Organization. A similar set of commands is GNU core utilities. The following are commands provided by until-linux. You can do man <command> or use the --help option to see what each command does. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) main() return https://yanevskiv.com/main-return?rev=1778758708&do=diff main() return The return value of int main(); function is called the program's exit status. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Math books https://yanevskiv.com/math-books?rev=1778758708&do=diff Math books * <https://zb260.user.srcf.net/notes/III/modrep.pdf> text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Mathematical Maturity https://yanevskiv.com/mathematical-maturity?rev=1778758708&do=diff Mathematical Maturity Trivial example One of the earliest awakenings of my mathematical maturity was when I was a kid, thinking one of the simplest equations there is: $$ a\cdot x = b$$ I knew how to solve this 99% of the time: $$x = b / a$$ Is this correct? Let's take the equation $2\cdot x = 6$$b = 0$$x = 0$$a = 0$$a = 0$$b = 3$$x$$0 = 3$$a = 0$$b = 0$$x$$0 = 0$$a\cdot x = b$$a\cdot x = b$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Matmul https://yanevskiv.com/matmul?rev=1778758708&do=diff Matmul Matmul is an algorithm in high-performance computing (HPC). It is a BLAS level 2 (“Basic Linear Algebra Subprograms”) algorithm. Definition Matrices Let $\mathbf A\in\mathbb{R}^{A_\text{rows}\times A_\text{cols}}$ and $\mathbf B\in \mathbb R^{B_\text{rows}\times B_\text{cols}}$ be square matrices over real numbers and let $A_\text{rows} = B_\text{cols}$. Matmul defined as a matrix multiplication $\mathbf A\cdot \mathbf B$$\mathbf C\in\mathbb{R}^{A_\text{rows}\times B_\text{cols}}$$$ … text/html 2026-05-25T13:47:37+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert -i\rangle$ https://yanevskiv.com/minus-i-state?rev=1779716857&do=diff $\lvert -i\rangle$ Minus-i state $\lvert -i\rangle$ (also written $\lvert -y\rangle$) is a quantum state that is an equal superposition of $\lvert 0\rangle$ and $\lvert 1\rangle$ with a relative phase of $-i$. It is one of the six cardinal states on the Bloch sphere, sitting at the negative $y$-axis with coordinates $(0, -1, 0)$. $$\lvert -i\rangle = \frac{1}{\sqrt{2}}\lvert 0\rangle - \frac{i}{\sqrt{2}}\lvert 1\rangle = \frac{1}{\sqrt{2}}\begin{pmatrix}1\\-i\end{pmatrix}$$ It is an eigenstat… text/html 2026-05-25T13:47:27+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert -\rangle$ https://yanevskiv.com/minus-state?rev=1779716847&do=diff $\lvert -\rangle$ Minus state $\lvert -\rangle$ is a quantum state that is an equal superposition of the two computational basis states $\lvert 0\rangle$ and $\lvert 1\rangle$ with opposite signs. It is one of the six cardinal states on the Bloch sphere, sitting at the negative $x$-axis. $$\lvert -\rangle = \frac{1}{\sqrt{2}}\lvert 0\rangle - \frac{1}{\sqrt{2}}\lvert 1\rangle = \frac{1}{\sqrt{2}}\begin{pmatrix}1\\-1\end{pmatrix}$$ When measured in the computational basis $\{\lvert 0\rangle, \… text/html 2026-05-25T13:47:11+00:00 Anonymous (anonymous@undisclosed.example.com) Mixed state https://yanevskiv.com/mixed-state?rev=1779716831&do=diff Mixed state Mixed state is a quantum state that cannot be described by a single state vector $\lvert\psi\rangle$. It arises when a quantum system is entangled with its environment or when there is classical uncertainty about how the system was prepared. Mixed states are represented by density matrices $\rho$$\rho = \lvert\psi\rangle\langle\psi\rvert$$\text{tr}(\rho^2) = 1$$\lvert 0\rangle$$p$$\lvert 1\rangle$$1-p$$$\rho = p\lvert 0\rangle\langle 0\rvert + (1-p)\lvert 1\rangle\langle 1\rvert = \… text/html 2026-05-25T13:48:57+00:00 Anonymous (anonymous@undisclosed.example.com) Multiqubit gates https://yanevskiv.com/multiqubit-gates?rev=1779716937&do=diff Multiqubit gates Multiqubit gates are quantum gates that act on two or more qubits simultaneously. Unlike single-qubit gates, multiqubit gates can create entanglement between qubits, which is an essential resource for quantum computation. A single-qubit gate is a $2\times 2$$4\times 4$$8\times 8$$n$$2^n \times 2^n$$U$$U$$\lvert 1\rangle$$X$$X$$n$$\{H, T, \text{CNOT}\}$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) My bookmarks https://yanevskiv.com/my-bookmarks?rev=1778758708&do=diff My bookmarks C++ * <https://en.cppreference.com/w/> * <https://json.nlohmann.me/api/basic_json/> LaTeX Online tools: * <https://openai.com/index/introducing-prism/> * <https://www.mathcha.io/> * <https://www.overleaf.com/> Documentation PDFs: * <https://pgfplots.sourceforge.net/pgfplots.pdf> * <https://www.bu.edu/math/files/2013/08/tikzpgfmanual.pdf> * <https://feog.github.io/chap1dm.pdf> Wikipedia Related to mathematics: * <https://en.wikipedia.org/wiki/Siamese_neural_network… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Name mangling https://yanevskiv.com/name-mangling?rev=1778758708&do=diff Name mangling Name mangling is how C++ compilers encode object types then and reconstruct the type back. Let's say we got a following piece of C++ code. namespace Hello { struct World { template <typename T> T add(T x, T y) { return x + y; } }; } text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Network Configuration https://yanevskiv.com/net-config?rev=1778758708&do=diff Network Configuration This article is about network configuration in GNU/Linux systems ifupdown Dynamic configurations Dynamic configuration with ifupdown (IPv4) # /etc/network/interfaces iface ens3 inet dhcp Dynamic configuration with ifupdwon (IPv6) text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) NIH syndrome https://yanevskiv.com/nih-syndrome?rev=1778758708&do=diff NIH syndrome NIH syndrome stands for “Not invented here” syndrome. It's when you deliberately avoid using a premade solution in favor of your own. For example, you might prefer to implement your own dynamic array even though std::vector<int> already exist. The commonly given rationale is that you'll probably find the implementation you made easier to understand (you wrote it!) and you'll be able easily make it fit your needs. text/html 2026-05-25T13:51:58+00:00 Anonymous (anonymous@undisclosed.example.com) NISQ https://yanevskiv.com/nisq?rev=1779717118&do=diff NISQ NISQ (Noisy Intermediate-Scale Quantum) refers to the current era of quantum computing, characterized by devices with tens to a few thousand qubits that are too noisy for full fault-tolerant quantum error correction. The term was coined by John Preskill in 2018.$10^{-3}$$10^{-2}$ text/html 2026-05-25T13:48:46+00:00 Anonymous (anonymous@undisclosed.example.com) NOON state https://yanevskiv.com/noon-state?rev=1779716926&do=diff NOON state NOON state is an entangled quantum state of two modes in which $N$ photons are in one mode and zero in the other, in an equal superposition with the reverse. It is written as: $$\lvert N\!:\!0\rangle\!\rangle = \frac{1}{\sqrt{2}}\left(\lvert N\rangle_a\lvert 0\rangle_b + \lvert 0\rangle_a\lvert N\rangle_b\right)$$ NOON states arise naturally in quantum metrology and quantum lithography. Their key property is phase sensitivity that scales as $1/N$$1/\sqrt{N}$$\sqrt{N}$$\phi$$a$$N$$N… text/html 2026-05-23T00:12:00+00:00 Anonymous (anonymous@undisclosed.example.com) Numbers every programmer should know https://yanevskiv.com/numbers-every-programmer-should-know?rev=1779495120&do=diff Numbers every programmer should know Numbers every programmer should know is a short document listing latencies of various computer operations. The list is given by a computer scientist Jeff Dean. It illustrates how various high-level operations exponentially take longer time to perform compared to various low-level operations. text/html 2026-05-18T12:49:54+00:00 Anonymous (anonymous@undisclosed.example.com) nvcc https://yanevskiv.com/nvcc?rev=1779108594&do=diff nvcc nvcc (or Nvidia C/C++ compiler) is a C++ compiler created by Nvidia that adds CUDA kernel syntax. $ nvcc kernel.cu text/html 2026-05-25T13:54:35+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert 1\rangle$ https://yanevskiv.com/one-state?rev=1779717275&do=diff $\lvert 1\rangle$ The one state $\lvert 1\rangle$ is one of the two computational basis states of a qubit. It is the quantum analogue of a classical 1 bit. The other computational basis state is $\lvert 0\rangle$. $$\lvert 1\rangle = \begin{pmatrix}0\\ 1\end{pmatrix}$$ On the Bloch sphere, $\lvert 1\rangle$ corresponds to the south pole at coordinates $(0, 0, -1)$. It is an eigenstate of the Pauli-Z gate with eigenvalue $-1$$Z\lvert 1\rangle = -\lvert 1\rangle$$\lvert 0\rangle$$\lvert 1\rangl… text/html 2026-05-25T13:49:13+00:00 Anonymous (anonymous@undisclosed.example.com) Phase gate https://yanevskiv.com/p-gate?rev=1779716953&do=diff Phase gate Phase gate (or P gate) is a single-qubit quantum gate that applies a phase shift $\phi$ to the $\lvert 1\rangle$ component of a qubit while leaving the $\lvert 0\rangle$ component unchanged. It is a rotation about the $z$-axis of the Bloch sphere. $$P(\phi) = \begin{pmatrix}1 & 0\\ 0 & e^{i\phi}\end{pmatrix}$$ Applied to a general qubit $\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$, the phase gate multiplies the $\lvert 1\rangle$$e^{i\phi}$$$P(\phi)\lvert\psi\rangle = a… text/html 2026-05-25T13:08:44+00:00 Anonymous (anonymous@undisclosed.example.com) Disclaimer https://yanevskiv.com/past-disclaimer?rev=1779714524&do=diff Disclaimer This website is not an authoritative source. It is written by one person -- me. It's not meant to serve as documentation or a definitive guide to the technology I talk about. I write about topics that interest me and I explain them in the way I understand them text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) /usr https://yanevskiv.com/path-usr?rev=1778758708&do=diff /usr * /usr/bin * /usr/include * /usr/lib * /usr/share * /usr/src text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) /var https://yanevskiv.com/path-var?rev=1778758708&do=diff /var * /var/cache * /var/db * /var/empty * /var/lib * /var/local * /var/lock * /var/log * /var/opt * /var/run * /var/www * /var/spool * /var/tmp text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Pauli gate https://yanevskiv.com/pauli-gate?rev=1778758708&do=diff Pauli gate Pauli gates are one of the three quantum gates $(X, Y, Z)$, which correspond to Pauli matrices $(\sigma_x, \sigma_y, \sigma_z)$, with the inclusion of the identity gate $I$. For a single qubit, they take the following matrix form $$I = \begin{pmatrix}1 & 0\\0 & 1\end{pmatrix}\quad X = \begin{pmatrix}0 & 1\\ 1 & 0\end{pmatrix}\quad Y = \begin{pmatrix}0 & i \\ -i & 0 \end{pmatrix}\quad Z = \begin{pmatrix}1 & 0 \\ 0 & -1\end{pmatrix}$$ They are involutory, meaning they square up to i… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) pdflatex https://yanevskiv.com/pdflatex?rev=1778758708&do=diff pdflatex pdflatex is the most common LaTeX compiler. You compile latex source code by running pdflatex main.tex. This creates a PDF file main.pdf. It also creates a log file main.log and an auxiliary file main.aux used to build references. You can ignore these latter two and text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) perf https://yanevskiv.com/perf?rev=1778758708&do=diff perf text/html 2026-05-14T13:28:01+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/playground?rev=1778765281&do=diff \documentclass{standalone} \begin{document} \end{document} text/html 2026-05-25T13:47:19+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert +\rangle$ https://yanevskiv.com/plus-state?rev=1779716839&do=diff $\lvert +\rangle$ Plus state $\lvert +\rangle$ is a quantum state that is an equal superposition of the two computational basis states $\lvert 0\rangle$ and $\lvert 1\rangle$ with equal positive amplitudes. It is one of the six cardinal states on the Bloch sphere, sitting at the positive $x$-axis. $$\lvert +\rangle = \frac{1}{\sqrt{2}}\lvert 0\rangle + \frac{1}{\sqrt{2}}\lvert 1\rangle = \frac{1}{\sqrt{2}}\begin{pmatrix}1\\1\end{pmatrix}$$ When measured in the computational basis $\{\lvert 0\… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) POSIX headers https://yanevskiv.com/posix-headers?rev=1778758708&do=diff POSIX headers POSIX headers are C programming language headers as defined by POSIX. Links * <https://pubs.opengroup.org/onlinepubs/9799919799/idx/head.html> text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) #pragma once https://yanevskiv.com/pragma-once?rev=1778758708&do=diff #pragma once In C and C++ programming languages #pragma once is a non-standard preprocessor directive that is equivalent to header guards. You just put #pragma once at the top, rather than wrapping the entire header within header guards. Header guards: // image.h #ifndef __IMAGE_H__ #define __IMAGE_H__ struct Image { ... }; #endif /* __IMAGE_H__ */ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Probability amplitude https://yanevskiv.com/probability-amplitude?rev=1778758708&do=diff Probability amplitude Probability amplitude is a complex number associated with a quantum state. The square modulus of that complex number is -- according to the Born rule -- the probability of finding the quantum system in that state. If we take $$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$ Concrete example text/html 2026-05-25T13:54:21+00:00 Anonymous (anonymous@undisclosed.example.com) Pure state https://yanevskiv.com/pure-state?rev=1779717261&do=diff Pure state Pure state is a quantum state that is completely described by a single state vector $\lvert\psi\rangle$. It carries the maximum possible information about a quantum system. When information about the system leaks into the environment the state becomes mixed — this process is called decoherence, and it is one of the primary challenges in quantum computing.$0\,\text{V}$$5\,\text{V}$$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$a$$b$$\lvert\psi\rangle$$\rho = \lvert\psi\rang… text/html 2026-05-25T13:52:12+00:00 Anonymous (anonymous@undisclosed.example.com) QAOA https://yanevskiv.com/qaoa?rev=1779717132&do=diff QAOA QAOA (Quantum Approximate Optimization Algorithm) is a hybrid quantum-classical algorithm for combinatorial optimization problems. It was introduced by Edward Farhi, Jeffrey Goldstone, and Sam Gutmann in 2014 and is one of the leading candidates for near-term quantum advantage on $p$$(\boldsymbol\gamma, \boldsymbol\beta)$$\lvert s\rangle = H^{\otimes n}\lvert 0\rangle^{\otimes n}$$H_C$$H_B = \sum_i X_i$$p$$$\lvert\boldsymbol{\gamma},\boldsymbol{\beta}\rangle = e^{-i\beta_p H_B}e^{-i\gamma_… text/html 2026-05-25T13:50:46+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum Fourier transform https://yanevskiv.com/qft?rev=1779717046&do=diff Quantum Fourier transform Quantum Fourier transform (QFT) is the quantum analogue of the discrete Fourier transform (DFT). It maps a computational basis state $\lvert j\rangle$ to a superposition whose amplitudes encode the DFT of the input amplitudes, for $N = 2^n$ states on $n$$$\text{QFT}\lvert j\rangle = \frac{1}{\sqrt{N}}\sum_{k=0}^{N-1} e^{2\pi ijk/N}\lvert k\rangle$$$O(n^2)$$n$$O(N \log N) = O(n \cdot 2^n)$$n$$n(n+1)/2$$$R_k = P\!\left(\frac{2\pi}{2^k}\right) = \begin{pmatrix}1 & 0 \\ 0 … text/html 2026-05-25T13:50:58+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum phase estimation https://yanevskiv.com/qpe?rev=1779717058&do=diff Quantum phase estimation Quantum phase estimation (QPE) is a quantum algorithm that estimates the eigenvalue phase $\phi$ of a unitary operator $U$ given access to an eigenstate $\lvert u\rangle$ of $U$. It is one of the most important subroutines in quantum computing, used as a building block in $U\lvert u\rangle = e^{2\pi i\phi}\lvert u\rangle$$\phi \in [0,1)$$\phi$$n$$n$$O(2^n)$$U$$n$$\lvert 0\rangle^{\otimes n}$$\lvert u\rangle$$n$$U^{2^k}$$k = 0, 1, \ldots, n-1$$k$$U^{2^k}$$$\lvert 0\rangl… text/html 2026-05-25T13:55:35+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum algorithm https://yanevskiv.com/quantum-algorithm?rev=1779717335&do=diff Quantum algorithm Quantum algorithm is an algorithm designed to run on a quantum computer, exploiting quantum phenomena such as superposition, entanglement, and interference to solve certain problems faster than any known classical algorithm. Quantum algorithms are expressed as sequences of quantum gates applied to a quantum register, followed by measurements. text/html 2026-05-25T13:50:13+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum circuit https://yanevskiv.com/quantum-circuit?rev=1779717013&do=diff Quantum circuit Quantum circuit is a model of quantum computation in which a sequence of quantum gates is applied to a quantum register. Quantum circuits are the quantum analogue of classical digital circuits, but instead of Boolean logic gates acting on bits they use unitary matrices acting on qubits.$\lvert 0\rangle^{\otimes n}$$d$$n$$nd$$\{H, T, \text{CNOT}\}$$\varepsilon$$O(\text{polylog}(1/\varepsilon))$$\lvert 0\rangle$$\lvert 1\rangle$ text/html 2026-05-25T10:14:19+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum gate https://yanevskiv.com/quantum-gate?rev=1779704059&do=diff Quantum gate Quantum gates are the quantum computing equivalent of classical logic gates like AND, OR, XOR, NOT. Classical logic gates are defined by their truth tables. They follow a mathematical structure called Boolean algebra. With the advancement of MOSFET transistor it became possible to implement these logic gates electrically. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum I gate https://yanevskiv.com/quantum-i-gate?rev=1778758708&do=diff Quantum I gate Quantum I gate (or Identity gate) is a quantum gate that leaves the quantum state unchanged. In quantum circuits it's commonly written as wire. In matrix form, it's equivalent to the identity matrix. $$I = \begin{pmatrix} 1 & 0\\ 0 & 1\end{pmatrix}$$ Effect Z basis states For states along the Z-axis: $$I\lvert 0\rangle =\lvert 0\rangle\qquad I\lvert 1\rangle = \lvert 1 \rangle$$$$I\lvert i\rangle =\lvert i\rangle\qquad I\lvert -i\rangle = \lvert -i \rangle$$$$I\lvert +\rangle… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum register https://yanevskiv.com/quantum-register?rev=1778758708&do=diff Quantum register Quantum register is a register made out of qubits. It is the quantum equivalent of a classical CPU register. A classical CPU registers such as x86-64 registers (rax rbx rcx rdx rdi rsi) are made out of 64 bits on modern CPU architectures. A 64-bit register can store any whole number from 0 to 18446744073709551616, which is big! The CPU can efficiently manipulate these by running instructions over them, such as $\lvert\psi\rangle$$a,b\in\mathbb{C}$$$\lvert\psi\rangle = a\lvert … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum X gate https://yanevskiv.com/quantum-x-gate?rev=1778758708&do=diff Quantum X gate Quantum X gate (or Pauli-X gate, quantum NOT gate) is a quantum gate that is analogous to the classical “NOT” or “bit flip”. For a single qubit, it applies a rotation around the X-axis by $\pi$ on the Bloch sphere. In matrix form, X gate is equivalently written as a Pauli matrix $\sigma_x$$$X = \begin{pmatrix}0 & 1\\ 1 & 0\end{pmatrix}$$$\lvert0\rangle,\lvert 1\rangle$$$X\lvert 0\rangle = \lvert 1\rangle\qquad X\lvert 1\rangle = \lvert 0\rangle$$$\lvert i\rangle, \lvert -i\rangle… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum Y gate https://yanevskiv.com/quantum-y-gate?rev=1778758708&do=diff Quantum Y gate Quantum Y gate (or Pauli-Y gate) is a quantum gate. It rotates the quantum state by $\pi$ degrees around the Y-axis on the Bloch sphere. In matrix form, it is equivalent to Pauli matrix $\sigma_y$ which is why it's commonly called Pauli-Y gate. $$Y = \begin{pmatrix}0 & -i\\ i & 0\end{pmatrix}$$ In some ways, it acts as an alternative to $\pi / 2$$i$$$Y\lvert 1\rangle = \lvert 0\rangle\qquad Y\lvert 0\rangle = \lvert 1 \rangle$$$$Y\lvert +\rangle = \lvert -\rangle\qquad Y\lvert … text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Quantum Z gate https://yanevskiv.com/quantum-z-gate?rev=1778758708&do=diff Quantum Z gate Quantum Z gate (or Pauli-Z gate, phase flip gate) is a quantum gate. It rotates the quantum state around the computational axis (the Z-axis) by $\pi$ degrees. In matrix form, it is equivalent to the Pauli-Z matrix $\sigma_z$. This is why it's commonly called Pauli-Z gate.$$Z = \begin{pmatrix}1 & 0 \\ 0 & -1\end{pmatrix}$$$\lvert 0\rangle$$\lvert 1\rangle$$\pi$$$Z\lvert 0\rangle = \lvert 0\rangle\qquad Z\lvert 1\rangle = -\lvert 1\rangle$$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Qubit gate https://yanevskiv.com/qubit-gates-in-c?rev=1778758708&do=diff Qubit gate Simulation In C99, a header <complex.h> is provided that implements complex numbers. State As we've seen, a qubit is a two-state configuration with complex probability amplitudes distributed between the two states. This gives us the following implementation of a single qubit: $$\lvert\psi\rangle = \alpha\lvert 0\rangle + \beta\lvert 1\rangle,\qquad \alpha,\beta\in\mathbb C$$$$\lVert\psi\lVert^2 = |\alpha|^2 + |\beta|^2 = \alpha\bar{\alpha} + \beta\bar{\beta}$$$$\lvert\psi\rangle\r… text/html 2026-05-25T13:16:45+00:00 Anonymous (anonymous@undisclosed.example.com) Qubit https://yanevskiv.com/qubit?rev=1779715005&do=diff Qubit Qubit is the quantum computing equivalent of a bit. A classical bit can be 0 or 1. There are no probabilities involved at all, but we can assign them anyway. If a bit is 1, then it's 1 with 100% probability and 0 with 0% probability. Conversely, if a bit is $\lvert 0\rangle$$\lvert 1\rangle$$\lvert 0\rangle$$\lvert 1\rangle$$\lvert\psi\rangle$$$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$$a$$b$$\lvert 0\rangle$$a = \frac{\sqrt 2}{2} + i\frac{\sqrt 2}{2}$$\lvert 1\rangle$$b =… text/html 2026-05-25T13:55:25+00:00 Anonymous (anonymous@undisclosed.example.com) Rotation gates https://yanevskiv.com/r-gate?rev=1779717325&do=diff Rotation gates Rotation gates $R_x(\theta)$, $R_y(\theta)$, $R_z(\theta)$ are single-qubit gates that rotate the Bloch vector by angle $\theta$ about the $x$-, $y$-, and $z$-axes respectively. They are defined via the matrix exponential of the corresponding Pauli matrices. $$R_x(\theta) = e^{-i\theta X/2}, \qquad R_y(\theta) = e^{-i\theta Y/2}, \qquad R_z(\theta) = e^{-i\theta Z/2}$$ Matrix form Applying the matrix exponential $e^{-i\theta P/2} = \cos(\theta/2)I - i\sin(\theta/2)P$$X^2 = Y^2… text/html 2026-05-25T13:52:51+00:00 Anonymous (anonymous@undisclosed.example.com) Rabi oscillations https://yanevskiv.com/rabi-cycles?rev=1779717171&do=diff Rabi oscillations Rabi oscillations (or Rabi cycles) are periodic oscillations in the state of a driven two-level quantum system. When a qubit is driven by a resonant electromagnetic field, its population continuously oscillates between $\lvert 0\rangle$ and $\lvert 1\rangle$ at the Rabi frequency $\Omega$$\omega = \omega_0$$\omega_0$$\Omega$$\lvert 1\rangle$$\lvert 0\rangle$$$P_1(t) = \sin^2\!\left(\frac{\Omega t}{2}\right), \qquad P_0(t) = \cos^2\!\left(\frac{\Omega t}{2}\right)$$$\lvert 0\ra… text/html 2026-05-25T13:53:06+00:00 Anonymous (anonymous@undisclosed.example.com) Ramsey interferometry https://yanevskiv.com/ramsey-interference?rev=1779717186&do=diff Ramsey interferometry Ramsey interferometry is a technique for measuring the transition frequency of a quantum system with very high precision using two separated pulses. It was developed by Norman Ramsey in 1950 as an improvement on Rabi's continuous-drive spectroscopy, and it forms the basis of modern atomic clocks and qubit frequency calibration.$\pi/2$$T$$\pi/2$$\lvert +\rangle$$\lvert 0\rangle$$T$$\delta T$$\delta = \omega - \omega_0$$\omega$$\omega_0$$\pi/2$$$P_1(T) = \frac{1}{2}(1 - \cos… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Ruin theory (personal finance) https://yanevskiv.com/ruin-theory?rev=1778758708&do=diff Ruin theory (personal finance) This article is supposed to illustrate using Cramer-Lundberg model from actuarial science and applying to personal finance. This model was invented in 1930s for insurance companies. Insurance companies never seem to go bankrupt yet ordinary people are often get financial struggles. While it's easy to blame insurance companies for cheating at the game and ripping us off (and there is certainly a lot of truth to that), perhaps we can also learn the game they're play… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Rule of 5 https://yanevskiv.com/rule-of-5?rev=1778758708&do=diff Rule of 5 In C++, rule of 5 * Destructor * Copy constructor * Move constructor * Copy assignment operator * Move assignment operator #pragma once struct Image { public: Image(); /* Todo */ }; Links * <https://en.cppreference.com/w/cpp/language/rule_of_three.html> text/html 2026-05-25T13:53:17+00:00 Anonymous (anonymous@undisclosed.example.com) Rotating wave approximation https://yanevskiv.com/rwa?rev=1779717197&do=diff Rotating wave approximation Rotating wave approximation (RWA) is an approximation in quantum optics and quantum control that simplifies the Hamiltonian of a driven quantum system by discarding rapidly oscillating terms. It reduces the full time-dependent driven Hamiltonian to a simpler time-independent one in the rotating frame, making $\omega_0$$\omega$$\delta = \omega - \omega_0$$\omega + \omega_0$$\omega$$\rho \to e^{i\omega t Z/2}\rho e^{-i\omega t Z/2}$$$H_{\text{RWA}} = \frac{\hbar}{2}\be… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) SAXPY https://yanevskiv.com/saxpy?rev=1778758708&do=diff SAXPY SAXPY is an algorithm in high-performance computing (HPC). Math Vectors Let $\mathbf{y}^{(t)}, \mathbf{x}^{(t)}\in\mathbb{R}^n$ be vectors over real numbers at some discrete time $t\in\mathbb{N}$ and let $a\in\mathbb{R}$ be a real parameter. SAXPY is defined as a vector update of $\mathbf{y}$ at time $t+1$ according to the formula: $$\mathbf{y}^{(t+1)} = a\mathbf{x}^{(t)} + \mathbf{y}^{(t)}$$ Elements $\mathbf{y}^{(t)} = (y_0^{(t)}, y_1^{(t)}, \dots, y_n^{(t)})$$\mathbf{x}^{(t)} = (… text/html 2026-05-23T00:03:05+00:00 Anonymous (anonymous@undisclosed.example.com) Schrödinger equation https://yanevskiv.com/schrodinger-equation?rev=1779494585&do=diff Schrödinger equation In quantum mechanics, wave function is a mathematical object used to describe a quantum particle. This wave function evolves according to the Schrödinger equation. For a single particle, the time-dependent 3-dimensional Schrödinger equation is stated as the following:$$ i\hbar \frac{\partial}{\partial t}\Psi = \left(-\frac{\hbar^2}{2m}\nabla^2 + V\right) \Psi$$$i$$i^2 + 1 = 0$$\hbar$$\hbar = h/2\pi$$\hbar \approx 1.054 571 817\times 10^{-34}J\cdot s$$\partial / \partial t$… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/semaphore.h?rev=1778758708&do=diff <semaphore.h> In C, <semaphore.h> is a header that offers POSIX semaphores. Manual * <https://pubs.opengroup.org/onlinepubs/7908799/xsh/semaphore.h.html> text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Semaphore https://yanevskiv.com/semaphore?rev=1778758708&do=diff Semaphore Semaphore is a synchronization primitive. It's used to control thread execution in multithreaded environments. A semaphore acts like an integer. An integer supports two well-known opeartions: increment i++ and decrement i--. A semaphore works in a similar way, except a semaphore cannot be decremented below zero. This is because semaphore takes action to protect its value against bankrupcy by taking hostage of threads that attempt to make it negative. text/html 2026-05-14T13:07:09+00:00 Anonymous (anonymous@undisclosed.example.com) Shell https://yanevskiv.com/shell?rev=1778764029&do=diff Shell What is a shell? Shell is a program that lets you to run other programs in the terminal. Shell allows you to pass command line arguments, set environment variables and redirect the program's stardard input / output / error. It allows you to chain programs, such that output from one program is redirected as input to another program. It also allows you to run the programs in the background. Basically, a shell allows you to easily orchestrate programs in the terminal. text/html 2026-05-25T13:51:22+00:00 Anonymous (anonymous@undisclosed.example.com) Shor's algorithm https://yanevskiv.com/shor?rev=1779717082&do=diff Shor's algorithm Shor's algorithm is a quantum algorithm that factors large integers in polynomial time. It was invented by Peter Shor in 1994 and is one of the most consequential results in quantum computing, because it would break the RSA public-key cryptosystem if run on a sufficiently large fault-tolerant quantum computer.$O(e^{O(n^{1/3}\log^{2/3} n)})$$n$$O(n^3)$$O(n)$$N$$a$$\gcd(a, N) = 1$$r$$a^r \equiv 1 \pmod{N}$$r$$a^{r/2} \not\equiv -1 \pmod{N}$$\gcd(a^{r/2} \pm 1, N)$$N$$1/2$$x \in \… text/html 2026-05-16T14:57:06+00:00 Anonymous (anonymous@undisclosed.example.com) ssh https://yanevskiv.com/ssh?rev=1778943426&do=diff ssh What is ssh? SSH (Secure shell) is a tool that allows you to remotely control another computer from your own. Login without password On the client, you should run the following command: ssh-keyring This command is going to generate two files in your text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) State vector https://yanevskiv.com/state-vector?rev=1778758708&do=diff State vector State vector is the vector representation of a quantum state. Quantum state is often written as a linear combination of basis states where the coefficients are probability amplitudes. For example, a qubit is often written in the following way using Dirac notation.$$\lvert\psi\rangle = a\lvert 0\rangle + b\lvert 1\rangle$$$\mathbb{C}^2$$\mathbb{C}^2$$\lvert\psi\rangle$$\mathbb{C}^2$$$\lvert\psi\rangle = \begin{pmatrix}a\\b\end{pmatrix}\qquad a,b\in\mathbb{C}$$$$\lvert\psi\rangle =… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/stdbool.h?rev=1778758708&do=diff <stdbool.h> In C programming language, <stdbool.h> is a header that's part of C standard library. It defines a boolean type bool as well as constants true and false. You need at least version C99 to use this header, so compile with gcc -std=c99 main.c -o program. text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/string.h?rev=1778758708&do=diff <string.h> In C programming language, <string.h> is a header for void* and char* types, presumably spanning many consequtive characters. Functions /* Memory functions */ void *memccpy(void *, const void *, int, size_t); void *memchr(const void *, int, size_t); int memcmp(const void *, const void *, size_t); void *memcpy(void *, const void *, size_t); void *memmove(void *, const void *, size_t); void *memset(void *, int, size_t); /* String functions */ char *strcat(cha… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Strunk & White https://yanevskiv.com/strunk-and-white?rev=1778758708&do=diff Strunk & White Strunk & White is a guide on writing text in the English language. The guide is contained in a book titled “The Elements of Style”. It was written written by William Strunk Jr. in the 1910s and later expanded by E. B. White in the 1950s. text/html 2026-05-25T13:49:53+00:00 Anonymous (anonymous@undisclosed.example.com) SWAP gate https://yanevskiv.com/swap-gate?rev=1779716993&do=diff SWAP gate SWAP gate is a two-qubit quantum gate that exchanges the states of two qubits. It is its own inverse ($\text{SWAP}^2 = I$) and is symmetric with respect to its two qubits. $$\text{SWAP} = \begin{pmatrix}1 & 0 & 0 & 0\\ 0 & 0 & 1 & 0\\ 0 & 1 & 0 & 0\\ 0 & 0 & 0 & 1\end{pmatrix}$$ The SWAP gate acts on the computational basis as follows. $$\text{SWAP}\lvert 00\rangle = \lvert 00\rangle, \quad \text{SWAP}\lvert 01\rangle = \lvert 10\rangle, \quad \text{SWAP}\lvert 10\rangle = \lvert 0… text/html 2026-05-14T13:39:10+00:00 Anonymous (anonymous@undisclosed.example.com) https://yanevskiv.com/syntax?rev=1778765950&do=diff [GitHub][gh] fdsafdsa text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Terminal https://yanevskiv.com/terminal?rev=1778758708&do=diff Terminal Terminal is conceptually anything that looks like a keyboard + a screen attached to a teletype device (TTY). It gives humans the ability to use the teletype device. When you type something in a terminal, the terminal sends your characters to the teletype device. When a teletype device responds, the terminal prints the result back to you. A terminal can also reinterpret the characters coming from the teletype device and change its behavior in some way (e.g. change cursor location or tu… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Test-driven development https://yanevskiv.com/test-driven-development?rev=1778758708&do=diff Test-driven development Test-driven development (or TDD) is a practice where you apprach software development in the following way: * You write a test. This test fails immediately, as you haven't even written any code yet. * You write the smallest piece of code that passes your test text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) ThinkPad https://yanevskiv.com/thinkpad?rev=1778758708&do=diff ThinkPad X-series x220ai text/html 2026-05-25T13:48:09+00:00 Anonymous (anonymous@undisclosed.example.com) Three qubits https://yanevskiv.com/three-qubits?rev=1779716889&do=diff Three qubits Three-qubit system is a quantum system consisting of three qubits. The state space is the tensor product $\mathbb{C}^2 \otimes \mathbb{C}^2 \otimes \mathbb{C}^2 \cong \mathbb{C}^8$, spanned by eight computational basis states. A general three-qubit state requires eight complex probability amplitudes. $$\lvert\psi\rangle = \sum_{x \in \{0,1\}^3} c_x\lvert x\rangle = c_{000}\lvert 000\rangle + c_{001}\lvert 001\rangle + c_{010}\lvert 010\rangle + c_{011}\lvert 011\rangle + \cdots + … text/html 2026-05-16T14:56:59+00:00 Anonymous (anonymous@undisclosed.example.com) tmux https://yanevskiv.com/tmux?rev=1778943419&do=diff tmux What is tmux? Tmux is a terminal multiplexer. It allows you to run multiple terminals in a single terminal. In this sense, it is an alternative to screen command. Tmux runs a background session that you can attach to. It gives you the ability to create multiple windows within a session. Then it also gives you the ability to create multiple panes within a window, and tile them. Each pane contains a terminal. Thus, you can think of tmux as a text/html 2026-05-14T13:16:11+00:00 Anonymous (anonymous@undisclosed.example.com) To do https://yanevskiv.com/todo?rev=1778764571&do=diff To do This page contains articles which I'm in the process of writing or plan to write about. Fix things * Annoying scroll when opening sitemap * Clicking on the logo should navigate to / instead of /home * Clean up the HTML in the page Website text/html 2026-05-25T13:49:45+00:00 Anonymous (anonymous@undisclosed.example.com) Toffoli gate https://yanevskiv.com/toffoli-gate?rev=1779716985&do=diff Toffoli gate Toffoli gate (also known as the CCNOT gate or doubly-controlled NOT) is a three-qubit quantum gate that flips the target qubit if and only if both control qubits are in state $\lvert 1\rangle$. It is named after Tommaso Toffoli, who introduced it in 1980.$\lvert a, b, c\rangle \mapsto \lvert a, b, c \oplus (a \wedge b)\rangle$$\oplus$$\wedge$$8\times 8$$8\times 8$$$\text{CCNOT} = \begin{pmatrix} 1 & 0 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 1 & 0 & 0 & 0 & 0 & 0 & 0\\ 0 & 0 & 1 & 0 & 0 & 0 &… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Topics I plan to write about https://yanevskiv.com/topics?rev=1778758708&do=diff Topics I plan to write about Wikipedia * Trace theory * Pi calculus * History monoid Concepts * Hazard pointer * ABA problem * Cache coherence (MSI MESI MOESI DragonFly) text/html 2026-05-25T13:47:49+00:00 Anonymous (anonymous@undisclosed.example.com) Two qubits https://yanevskiv.com/two-qubits?rev=1779716869&do=diff Two qubits Two-qubit system is a quantum system consisting of two qubits. The state space is the tensor product $\mathbb{C}^2 \otimes \mathbb{C}^2 \cong \mathbb{C}^4$, and a general two-qubit state is a superposition over four computational basis states: $\lvert 00\rangle$, $\lvert 01\rangle$, $\lvert 10\rangle$, and $\lvert 11\rangle$. A general two-qubit state $\lvert\psi\rangle$ requires four complex probability amplitudes $c_{00}, c_{01}, c_{10}, c_{11} \in \mathbb{C}$$|c_{00}|^2 + |c_{01}… text/html 2026-05-25T13:49:24+00:00 Anonymous (anonymous@undisclosed.example.com) U gate https://yanevskiv.com/u-gate?rev=1779716964&do=diff U gate U gate is the most general single-qubit unitary gate, parameterized by three real angles $\theta$, $\phi$, $\lambda$. Every single-qubit unitary operation (up to global phase) can be expressed as $U(\theta, \phi, \lambda)$ for some choice of these angles. $$U(\theta, \phi, \lambda) = \begin{pmatrix}\cos\dfrac{\theta}{2} & -e^{i\lambda}\sin\dfrac{\theta}{2}\\[6pt] e^{i\phi}\sin\dfrac{\theta}{2} & e^{i(\phi+\lambda)}\cos\dfrac{\theta}{2}\end{pmatrix}$$ The parameter $\theta$ controls how… text/html 2026-05-16T14:58:13+00:00 Anonymous (anonymous@undisclosed.example.com) VPS https://yanevskiv.com/vps?rev=1778943493&do=diff VPS What is a VPS? VPS (Virtual private server) is a virtual computer that you can buy from a cloud provider. It can do almost anything a real computer can. A VPS slice is often a virtual machine (QEMU + KVM) given to you by a cloud privder, with GNU/Linux pre-installed. text/html 2026-05-25T13:52:23+00:00 Anonymous (anonymous@undisclosed.example.com) VQE https://yanevskiv.com/vqe?rev=1779717143&do=diff VQE VQE (Variational Quantum Eigensolver) is a hybrid quantum-classical algorithm for estimating the ground state energy of a quantum system. It was proposed in 2014 by Peruzzo et al. and is one of the most important algorithms for near-term NISQ devices, with applications in quantum chemistry and materials science.$\lvert\psi(\boldsymbol\theta)\rangle$$H$$E_0$$$E_0 \leq \langle\psi(\boldsymbol\theta)\rvert H\lvert\psi(\boldsymbol\theta)\rangle$$$\lvert\psi(\boldsymbol\theta)\rangle$$\boldsymbo… text/html 2026-05-25T13:48:35+00:00 Anonymous (anonymous@undisclosed.example.com) W state https://yanevskiv.com/w-state?rev=1779716915&do=diff W state W state is an entangled three-qubit state that is an equal superposition over all configurations with exactly one qubit in state $\lvert 1\rangle$ and the others in $\lvert 0\rangle$. $$\lvert W\rangle = \frac{1}{\sqrt{3}}(\lvert 001\rangle + \lvert 010\rangle + \lvert 100\rangle)$$ The W state was identified by Wolfgang Dür, Guifré Vidal, and J. Ignacio Cirac in 2000 as part of their classification of three-qubit entanglement. Unlike the $n$$n$$\lvert 1\rangle$$$\lvert W_n\rangle = \… text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) (WIP) Work in Progress https://yanevskiv.com/wip-example?rev=1778758708&do=diff (WIP) Work in Progress text/html 2026-05-25T13:38:32+00:00 Anonymous (anonymous@undisclosed.example.com) Writing guide https://yanevskiv.com/writing-guide?rev=1779716312&do=diff Writing guide Writing guide (this article) is a guide to writing articles in this wiki. Every article should preferably start with a main section followed by a few paragraphs. The first paragraph should preferably start with the name of the article in bold (just as it did in this article) followed by a few sentences that further describe the concept.$\alpha,\beta,\gamma$$X$$$X = \begin{pmatrix} 0 & 1 \\ 1 & 0 \end{pmatrix}$$ text/html 2026-05-25T10:21:12+00:00 Anonymous (anonymous@undisclosed.example.com) X-gate https://yanevskiv.com/x-gate?rev=1779704472&do=diff X-gate X-gate (or Pauli-X gate / Quantum NOT gate) is a 1-qubit quantum gate that serves as the quantum equivalent of logical NOT. It's represented by the following 2×2 matrix. $$ X = \begin{pmatrix}0 & 1\\ 1 & 0\end{pmatrix}$$ The gate flips $\lvert 0\rangle$ to $\lvert 1\rangle$, and $\lvert 1\rangle$ to $\lvert 0\rangle$, which is why it's called the quantum equivalent of NOT.$\pi$ text/html 2026-05-25T19:22:43+00:00 Anonymous (anonymous@undisclosed.example.com) GPU Rendering Artifacts on ThinkPad X220 with Hyprland — Diagnosis & Fix https://yanevskiv.com/x220-gpu-rendering-with-hyprland?rev=1779736963&do=diff GPU Rendering Artifacts on ThinkPad X220 with Hyprland — Diagnosis & Fix Hardware & Software Context ------ Machine Lenovo ThinkPad X220 (4291SWP) GPU Intel HD Graphics 3000 — Sandy Bridge, Gen 6 Kernel driver i915 Mesa driver crocus (Gallium3D for Intel Gen 4–8) text/html 2026-05-25T13:55:02+00:00 Anonymous (anonymous@undisclosed.example.com) Y gate https://yanevskiv.com/y-gate?rev=1779717302&do=diff Y gate Y gate (or Pauli-Y gate) is a single-qubit quantum gate represented by the second Pauli matrix. It combines the actions of the X gate (bit flip) and the Z gate (phase flip), and also introduces a factor of $i$. $$Y = \begin{pmatrix}0 & -i \\ i & 0\end{pmatrix}$$ The gate maps the computational basis states as $Y\lvert 0\rangle = i\lvert 1\rangle$$Y\lvert 1\rangle = -i\lvert 0\rangle$$\pi$$y$$Y$$Y^\dagger = Y$$Y^\dagger Y = I$$Y^2 = I$$Y = iXZ$$\lvert i\rangle$$+1$$\lvert -i\rangle$$-1$ text/html 2026-05-14T11:38:28+00:00 Anonymous (anonymous@undisclosed.example.com) Wiki https://yanevskiv.com/yanevskiv-wiki?rev=1778758708&do=diff Wiki This is a meta article about this website. This website is my creation Challenges Writing this website presents some unique challenges. How do I write down my notes but also make the information useful to the reader? If this website was only about putting my notes, I wouldn't have to use words at all. I could make articles where I just slap some links and call it a day. That would be useful to me, but not to the wider audience. text/html 2026-05-25T13:55:14+00:00 Anonymous (anonymous@undisclosed.example.com) Z gate https://yanevskiv.com/z-gate?rev=1779717314&do=diff Z gate Z gate (or Pauli-Z gate) is a single-qubit quantum gate that applies a phase flip to the $\lvert 1\rangle$ state while leaving $\lvert 0\rangle$ unchanged. It is the third Pauli matrix and a special case of the phase gate $P(\pi)$. $$Z = \begin{pmatrix}1 & 0\\ 0 & -1\end{pmatrix}$$ The Z gate maps the computational basis states as $Z\lvert 0\rangle = \lvert 0\rangle$ and $Z\lvert 1\rangle = -\lvert 1\rangle$. It does not change measurement outcomes in the computational basis (since $|-… text/html 2026-05-25T13:54:28+00:00 Anonymous (anonymous@undisclosed.example.com) $\lvert 0\rangle$ https://yanevskiv.com/zero-state?rev=1779717268&do=diff $\lvert 0\rangle$ The zero state $\lvert 0\rangle$ is one of the two computational basis states of a qubit. It is the quantum analogue of a classical 0 bit, and it is the standard initial state used in most quantum circuits. The other computational basis state is $\lvert 1\rangle$. $$\lvert 0\rangle = \begin{pmatrix}1\\0\end{pmatrix}$$$\lvert 0\rangle$$(0, 0, 1)$$+1$$Z\lvert 0\rangle = \lvert 0\rangle$$\lvert 0\rangle$$\lvert +\rangle = (\lvert 0\rangle + \lvert 1\rangle)/\sqrt{2}$