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

Contents

Automatic vectorization and vectorization inhibitors, exit criteria

An exit statement should in general be avoided. If the exit statement contains data-dependent conditions, the loop cannot be vectorized. The following is an example of a non-vectorizable loop

  for (int j = 0; j < n; j++) {
    a[j] = cos(j*1.0);
    if (a[j] < 0 ) break;
  }

Avoid loop termination conditions and opt for a single entry loop variable \( n \). The lower and upper bounds have to be kept fixed within the loop.