# Simulation kernels (1D FDTD)

**Simulation kernels** implement the same field updates with different execution strategies. The public run function dispatches according to the selected acceleration mode:

```c
void Fdtd_EzSimRun(Fdtd_EzSim *sim, size_t nsteps)
{
    switch (sim->fsim_state->fs_accel) {
        case FDTD_ACCEL_NONE: {
            Fdtd_KernelSerial_EzSimRun(sim, nsteps);
        } break;
        case FDTD_ACCEL_OPENMP: {
            Fdtd_KernelOpenMP_EzSimRun(sim, nsteps);
        } break;
    }
}
```

Both receive the same simulation object and requested step count. Switching modes changes execution, without rebuilding the fields or material representation.

Use `Fdtd_EzSimSetAccel(sim, FDTD_ACCEL_OPENMP)` to select the parallel path, or `--set-accel=openmp` in the driver. The [[fdtd-openmp-serial-kernel|serial kernel]] supplies a baseline; the [[fdtd-openmp-openmp-kernel|OpenMP kernel]] distributes spatial updates and synchronizes their phases.

Source: [fdtd_ez_sim.c](https://github.com/yanevskiv/fdtd-openmp/blob/main/src/fdtd/Ez/fdtd_ez_sim.c).