On 9/16/2010 9:58 AM, David Zhang wrote:
It's compiler specific I think.  I've done this with OpenMPI no problem, however on one another cluster with ifort I've gotten error messages about not using MPI_IN_PLACE.  So I think if it compiles, it should work fine.

On Thu, Sep 16, 2010 at 10:01 AM, Tom Rosmond <rosmond@reachone.com> wrote:
I am working with a Fortran 90 code with many MPI calls like this:

call mpi_gatherv(x,nsize(rank+1),
    mpi_real,x,nsize,nstep,mpi_real,root,mpi_comm_world,mstat)

Compiler can't affect what happens here (unless maybe you use x again somewhere).  Maybe you mean MPI library?  Intel MPI probably checks this at run time and issues an error. 
I've dealt with run-time errors (which surfaced along with an ifort upgrade) which caused silent failure (incorrect numerics) on openmpi but a fatal diagnostic from Intel MPI run-time, due to multiple uses of the same buffer.    Moral: even if it works for you now with openmpi, you could be setting up for unexpected failure in the future.
-- 
Tim Prince