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--- collapse-openmp [June 11, 2026 at 07:42] – created - external edit 127.0.0.1
+++ collapse-openmp [Unknown date] (current) – removed - external edit (Unknown date) 127.0.0.1
@@ Line 1: / Line 1: @@
-# Collapse (OpenMP)
-**Collapse** is an OpenMP clause that merges multiple perfectly-nested loops into a single flat iteration space before distributing work across threads. When a loop nest has too few outer iterations to keep all threads busy, distributing only the outer loop leaves most threads idle. `collapse(N)` multiplies the available parallelism by treating the combined iteration space as one loop. "Perfectly nested" means no statements appear between the loop headers.
-```c
-#pragma omp parallel for collapse(2)
-for (int i = 0; i < M; i++) {
-    for (int j = 0; j < N; j++) {
-        a[i][j] = b[i][j] * c[i][j];
-    }
-}
-```
-Without `collapse(2)`, a 4-thread run on a loop with `M = 2` would use at most 2 threads. With it, the iteration space is `M * N`, and all 4 threads stay busy. The combined iteration space is split and scheduled according to the `schedule` clause as usual.