Thanks guys for your answers.
Actually, the optimization was not disabled, and that was the problem, compiling it with -o0 solves it. Sorry. Oscar Mojica Geologist Ph.D. in Geophysics SENAI CIMATEC Supercomputing Center Lattes: http://lattes.cnpq.br/0796232840554652 ________________________________ From: users <users-boun...@lists.open-mpi.org> on behalf of Yann Jobic <yann.jo...@univ-amu.fr> Sent: Monday, January 16, 2017 12:01 PM To: Open MPI Users Subject: Re: [OMPI users] Rounding errors and MPI Hi, Is there an overlapping section in the MPI part ? Otherwise, please check : - declaration type of all the variables (consistency) - correct initialization of the array "wave" (to zero) - maybe use temporary variables like real size1,size2,factor size1 = dx+dy size2 = dhx+dhy factor = dt*size2/(size1**2) and then in the big loop: wave(it,j,k)= wave(it,j,k)*factor The code will also run faster. Yann Le 16/01/2017 à 14:28, Oscar Mojica a écrit : Hello everybody I'm having a problem with a parallel program written in fortran. I have a 3D array which is divided in two in the third dimension so thats two processes perform some operations with a part of the cube, using a subroutine. Each process also has the complete cube. Before each process call the subroutine, I compare its sub array with its corresponding part of the whole cube. These are the same. The subroutine simply performs point-to-point operations in a loop, i.e. do k=k1,k2 do j=1,nhx do it=1,nt wave(it,j,k)= wave(it,j,k)*dt/(dx+dy)*(dhx+dhy)/(dx+dy) end do end do enddo where, wave is the 3D array and the other values are constants. After leaving the subroutine I notice that there is a difference in the values calculated by process 1 compared to the values that I get if the whole cube is passed to the subroutine but that this only works on its part, i.e. --- complete 2017-01-12 10:30:23.000000000 -0400 +++ half 2017-01-12 10:34:57.000000000 -0400 @@ -4132545,7 +4132545,7 @@ -2.5386049E-04 -2.9899486E-04 -3.4697619E-04 - -3.7867704E-04 + -3.7867710E-04 0.0000000E+00 0.0000000E+00 0.0000000E+00 When I do this with more processes the same thing happens with all processes other than zero. I find it very strange. I am disabling the optimization when compiling. In the end the results are visually the same, but not numerically. I am working with simple precision. Any idea what may be going on? I do not know if this is related to MPI Oscar Mojica Geologist Ph.D. in Geophysics SENAI CIMATEC Supercomputing Center Lattes: http://lattes.cnpq.br/0796232840554652 _______________________________________________ users mailing list users@lists.open-mpi.org<mailto:users@lists.open-mpi.org> https://rfd.newmexicoconsortium.org/mailman/listinfo/users
_______________________________________________ users mailing list users@lists.open-mpi.org https://rfd.newmexicoconsortium.org/mailman/listinfo/users
