Computational Physics Lectures: How to optimize codes, from vectorization to parallelization

Contents

Automatic vectorization and vectorization inhibitors, more data dependencies

On the other hand, a so-called write-after-read statement can be vectorized. The following code

  double b = 15.;
  for (int i = 1; i < n; i++) {
      a[i-1] = a[i] + b;
  }

is an example of flow dependency that can be vectorized since no iteration with a higher value of \( i \) can complete before an iteration with a lower value of \( i \). However, such code leads to problems with parallelization.