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

 

 

 

Automatic vectorization and vectorization inhibitors, nested loops

Only the innermost loop of the following example is vectorized 

  for (int i = 0; i < n; i++) {
      for (int j = 0; j < n; j++) {
           a[i][j] += b[i][j];
      }  
  }

The exception is if an original outer loop is transformed into an inner loop as the result of compiler optimizations.