If compiling with -O0 solves the problem, then you should use -assume protect-parens and/or one of the options discussed in the PDF you will find at https://software.intel.com/en-us/articles/consistency-of-floating-point-results-using-the-intel-compiler. Disabling optimization is a heavy hammer that you don't want to use if you care about performance at all. If you are using Fortran and MPI, it seems likely you care about performance.
Jeff On Mon, Jan 16, 2017 at 8:31 AM, Oscar Mojica <o_moji...@hotmail.com> wrote: > 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 > listus...@lists.open-mpi.orghttps://rfd.newmexicoconsortium.org/mailman/listinfo/users > > > > _______________________________________________ > users mailing list > users@lists.open-mpi.org > https://rfd.newmexicoconsortium.org/mailman/listinfo/users > -- Jeff Hammond jeff.scie...@gmail.com http://jeffhammond.github.io/
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