Fortran#

Getting Started#

This section provides the minimum amount of information necessary to successfully compile a basic Fortran code, and then a basic Fortran MPI code. See External Resources for general Fortran language tutorials and Fortran-MPI tutorials. See Compilers for detailed compiler and programming environment information.

Hello World#

First, we must choose the compiler with which to compile our program. We can choose between the GNU, Intel, Nvidia, and Cray compilers.

To see available versions of a chosen compiler, use module avail. For this example, we'll use gfortran, which is part of GNU's gcc package:

module avail gcc
   gcc/10.3.0          gcc/11.2.0          gcc/12.1.0(default)

To load a particular compiler, use module load. We'll use gcc/12.1.0.

module load gcc/12.1.0

Create a file named hello.f90, and save the following text to the file:

PROGRAM hello

write(*,*) "Hello World"

END PROGRAM hello

Now, we can compile the program with the following command:

gfortran hello.f90 -o hello

This creates an executable named hello. Execute it by typing the following into your terminal:

./hello

It should return the following output:

Hello World

Hello World in MPI Parallel#

Now that we have a working Hello World program, let's modify it to run on multiple MPI tasks.

On Kestrel, there are multiple implementations of MPI available. We can choose between OpenMPI, Intel MPI, MPICH, and Cray MPICH. These MPI implementations are associated with an underlying Fortran compiler. For example, if we type:

module avail openmpi

we find that both openmpi/4.1.4-gcc and openmpi/4.1.4-intel are available.

Let's choose the openmpi/gcc combination:

module load openmpi/4.1.4-gcc

Now, create a new file named hello_mpi.f90 and save the following contents to the file:

PROGRAM hello_mpi
include 'mpif.h'

integer :: ierr, my_rank, number_of_ranks

call MPI_INIT(ierr)
call MPI_COMM_SIZE(MPI_COMM_WORLD, number_of_ranks, ierr)
call MPI_COMM_RANK(MPI_COMM_WORLD, my_rank, ierr)

write(*,*) "Hello World from MPI task: ", my_rank, "out of ", number_of_ranks

call MPI_FINALIZE(ierr)

END PROGRAM hello_mpi

To compile this program, type:

mpif90 hello_mpi.f90 -o hello_mpi

To run this code on the login node, type:

mpirun -n 4 ./hello_mpi

You should receive a similar output to the following (the rank ordering may differ):

 Hello World from MPI task:            1 out of            4
 Hello World from MPI task:            2 out of            4
 Hello World from MPI task:            3 out of            4
 Hello World from MPI task:            0 out of            4

Generally, we don't want to run MPI programs on the login node! Let's submit this as a job to the scheduler. Create a file named job.in and modify the file to contain the following:

#!/bin/bash

#SBATCH --time=00:01:00
#SBATCH --nodes=1
#SBATCH --ntasks-per-node=4
#SBATCH --partition=standard
#SBATCH --account=<your account here>

module load openmpi/4.1.4-gcc

srun -n 4 ./hello_mpi &> hello.out

Be sure to replace the <your account here> with your account name.

Submit the job:

sbatch job.in

When the job is done, the file hello.out should contain the same output as you found before (the ordering of ranks may differ).

Compilers#

Standalone compilers:#

Compiler	Compiler Executable	Module Avail	Systems available on
GNU (gcc)	gfortran	gcc	Kestrel(Eagle), Swift, Vermillion
Intel	ifort	intel-oneapi	Kestrel(Eagle), Swift, Vermillion
Intel	ifort	intel-classic	Kestrel

Fortran-MPI compilers#

Compiler	MPI	Compiler Executable	Module Avail	Systems available on
GNU (gcc)	openmpi	mpifort	openmpi	Kestrel(Eagle), Swift, Vermillion
intel	openmpi	mpifort	openmpi/4.1.x-intel	Kestrel(Eagle)
intel	intel	mpiifort	intel-oneapi-mpi	Kestrel, Swift, Vermillion
gcc	MPICH	mpifort	mpich	Kestrel, Swift, Vermillion
intel	MPICH	mpifort	mpich/4.0.2-intel	Kestrel only
cray	MPICH	ftn	cray-mpich	Kestrel only