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Subject: [OMPI devel] MPI_Reduce() is losing precision
From: Santhosh Kokala (Santhosh.Kokala_at_[hidden])
Date: 2012-10-15 02:06:32


Hi All,
I am having a strange problem with the floating precision. I get correct precision when I launch with one process, but when the same code is launched with 2 or more process I am losing precision in MPI_Redcue(..., MPI_FLOAT, MPI_SUM..); call. Output from my code

(admin)host:~$ mpirun -np 1 string 10 0.1 0.9 10 3
sum = 1
sum = 0.999992
sum = 1.00043

(admin)host:~$ mpirun -np 2 string 10 0.1 0.9 10 3
sum = 1
sum = 1
sum = 1.00049

As you can see I am loosing precision. Can someone help me fix this code? Last parameter to my code is the number of iterations. I am attaching source code to this email.

Santhosh