Re: [AMBER-Developers] ti_decomp_sc problem

From: <>
Date: Tue, 13 Apr 2010 11:55:33 -0400 (EDT)


I had a look at the ti_decomp_case. It hanged for me as well.

The hang is caused in sander.f, ca line 353:

         if (ifsc > 0) then
            partner = ieor(masterrank,1)
            if (nat == natom) then
               nrank = masterrank
               nrank = partner
            end if
            call mpi_bcast(jgroup, nat, MPI_INTEGER, nrank, commmaster, ierr)
         end if

I did not understand why nrank is computed this way. But in the test case
it comes out as 0 and 1 for the two processes, causing the following
mpi_bcast to hang, since both processes think they should talk and no one
listens (an all too common problem, not only in parallel programming...)

Replacing the nrank with a 0 in the mpi_bcast call fixes the problem (and
makes the preceeding five lines obsolete) and the test case runs through.
However, I do not know if this breaks decomp in other cases, since the
test has the same number of atoms on both prmtops. In a more typical SC
case with different atom numbers, this might work out different, but I
have nothing to compare...

Kind Regards,


Dr. Thomas Steinbrecher
BioMaps Institute
Rutgers University
610 Taylor Rd.
Piscataway, NJ 08854

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Received on Tue Apr 13 2010 - 09:00:08 PDT
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