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Reduction operations on arrays are among the more useful of the Fortran 90 intrinsics, especially when a parallel implementation is available. The best way to see how these reduction operations operate is to study a few instances where they are used in a program.
- Global operations involving every element
REAL :: a(1024), b(4,1024)
scalar = SUM(a) ! sum of all elements
a = PRODUCT(b, DIM=1) ! product of elts in first dim
scalar = COUNT(a == 0) ! gives number of zero elements
scalar = MAXVAL(a, MASK=a.LT.0) ! largest negative element
- Logical reductions: ANY, ALL
LOGICAL a(n)
REAL, DIMENSION(n) :: b, c
IF ( ALL(a) ) ... ! global AND
IF ( ALL(b == c) ) ... ! true if all elts equal
IF ( ANY(a) ) ... ! global OR
IF ( ANY(b < 0.0) ) ... ! true if any elt < 0.0
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