The (Flawed) Plan For a Good Reduction

I=9

• Incorrect parallel program:

c$omp parallel private(suml,i)

c$omp& shared(sum,a,n)

suml = 0.0

c$omp do

do 10 i=1,n

10 suml = suml + a(i)

cBug -- Must use critical section next!!!

sum = sum + suml

c$omp end parallel

Parallel Do

I=1

I=2

I=3

I=4

I=5

I=6

Initialize

Final Sum

suml = suml

suml = suml

suml = suml

Should have

been Synched

suml = 0.0

suml = 0.0

suml = 0.0

I=7

I=8

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