Some advices on the improvement of performance

Below we shall give some advices of how to improve the performance of a code.

• Use only clean loops without IF, GOTO or CALL statements. For example:

              DO i = 1, n
                 IF ( var > 0 ) THEN
                    a(i) = 0.
                 ELSE
                    a(i) = b(i)
                 ENDIF
              ENDDO
  

  should be replaced by

              IF ( var > 0 ) THEN
                 a(:) = 0.
              ELSE
                 a(:) = b(:)
              ENDIF
  

• Make sure that the inner loop is the longest one of a series of nested do loops.
• Use the inner loop for the first index of multi-dimensional arrays in case of nested loops. This may increase the efficiency, provided the inner loop is long enough.
• Avoid indirect addressing, if possible.
• Avoid division in a do loop.
• Avoid (seemingly) recursions in a loop.