Basic HTML version of Foils prepared August 29 98

Foil 44 Reductions

From Designing and Building Parallel Programs 2: openMP Shared Memory Programming Language DoD Modernization Tutorial -- 1995-1998. by Ian Foster, Gina Goff, Ehtesham Hayder, Chuck Koelbel(Some foils prepared by Kuck & Associates, Inc.)
1 Serial program is a reduction:
2 sum = 0.0
3 do 10 i=1,n
4 10 sum = sum + a(i)
5 Correct (but slow) program:
6 sum = 0.0
7 c$omp parallel private(i) shared(sum,a,n)
8 c$omp pdo
9 do 10 i=1,n
10 c$omp critical
11 sum = sum + a(i)
12 c$omp end critical
13 10 continue
14 c$omp end parallel
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