MPI Fortran compiler optimization error [duplicate]

Answer 1

Using the Fortran 90 interface to MPI reveals a mismatch in your call to MPI_RECV

      call MPI_RECV(prntMat(1:10, 1:10), 100, MPI_INTEGER, 1, 1, MPI_COMM_WORLD, stVal, ierr)
                                                                                            1
Error: There is no specific subroutine for the generic ‘mpi_recv’ at (1)

This is because the status variable stVal is an integer scalar, rather than an array of MPI_STATUS_SIZE. The F77 interface (include 'mpif.h') to MPI_RECV is:

INCLUDE ’mpif.h’
MPI_RECV(BUF, COUNT, DATATYPE, SOURCE, TAG, COMM, STATUS, IERROR)
<type>    BUF(*)
INTEGER    COUNT, DATATYPE, SOURCE, TAG, COMM
INTEGER    STATUS(MPI_STATUS_SIZE), IERROR

Changing

integer :: rank, ierr, stVal

to

integer :: rank, ierr, stVal(mpi_status_size)

produces a program that works as expected, tested with gfortran 5.1 and OpenMPI 1.8.5.

Using the F90 interface (use mpi vs include "mpif.h") lets the compiler detect the mismatched arguments at compile time rather than producing confusing runtime problems.