Using MPIFXΒΆ

Before you can use the MPIFX routines you need the following steps:

  1. Use the module libmpifx_module in your routines.
  2. Initialize the MPI framework via the mpifx_init() routine. (If you already initialized it via the legacy mpi_init() call, you can omit this step.
  3. Initialize a communicator of type(mpifx_comm).

Below you find a self containing example for reduction on all processes using a wrapper around mpi_allreduce():

program test_allreduce
  use libmpifx_module
  implicit none

  integer, parameter :: dp = kind(1.0d0)

  type(mpifx_comm) :: mycomm
  integer :: vali0, resvali0
  real(dp) :: valr(3), resvalr(3)

  call mpifx_init()
  call mycomm%init()

  ! Reduce scalar value
  vali0 = mycomm%rank * 2  ! Some arbitrary number
  write(*, "(I2.2,'-',I3.3,'|',1X,A,I0)") 1, mycomm%rank, &
      & "Value to be operated on:", vali0
  call mpifx_allreduce(mycomm, vali0, resvali0, MPI_SUM)
  write(*, "(I2.2,'-',I3.3,'|',1X,A,I0)") 2, mycomm%rank, &
      & "Obtained result (sum):", resvali0

  ! Reduce vector
  valr(:) = [ real(mycomm%rank + 1, dp) * 1.2, &
      & real(mycomm%rank + 1, dp) * 4.3, real(mycomm%rank + 1, dp) * 3.8 ]
  write(*, "(I2.2,'-',I3.3,'|',1X,A,3F8.2)") 3, mycomm%rank, &
      & "Value to be operated on:", valr(:)
  call mpifx_allreduce(mycomm, valr, resvalr, MPI_PROD)
  write(*, "(I2.2,'-',I3.3,'|',1X,A,3F8.2)") 4, mycomm%rank, &
      & "Obtained result (prod):", resvalr(:)
  call mpifx_finalize()

end program test_allreduce

When running on 4 processors:

mpirun -n 4 test_allreduce | sort

you should obtain the following output:

01-000| Value to be operated on:0
01-001| Value to be operated on:2
01-002| Value to be operated on:4
01-003| Value to be operated on:6
02-000| Obtained result (sum):12
02-001| Obtained result (sum):12
02-002| Obtained result (sum):12
02-003| Obtained result (sum):12
03-000| Value to be operated on:    1.20    4.30    3.80
03-001| Value to be operated on:    2.40    8.60    7.60
03-002| Value to be operated on:    3.60   12.90   11.40
03-003| Value to be operated on:    4.80   17.20   15.20
04-000| Obtained result (prod):   49.77 8205.12 5004.33
04-001| Obtained result (prod):   49.77 8205.12 5004.33
04-002| Obtained result (prod):   49.77 8205.12 5004.33
04-003| Obtained result (prod):   49.77 8205.12 5004.33

Have a look at the test folder in the source tree for further examples.