HP XC System 2.x Software - Manual (Page 113)

parallelism. For information about running more complex applications, refer to the HP-MPI
user documentation.
8.3.2.1 Example Application hello_world
To quickly become familiar with compiling and running HP-MPI programs, start with the C
version of a familiar
hello_world program. This program is called hello_world.c and
prints out the text string “Hello world! I’m r of s on host”. In this text string:
• r is the rank of the process
• s is the size of the communicator
• host is the host on which the program is run
The processor name is the host name for this implementation.
The source code for hello_world.c is stored in $MPI_ROOT/help and is shown below.
#include <stdio.h>
#include <mpi.h>
void main(argc, argv)
int argc; char *argv[];
{
int rank, size, len;
char name[MPI_MAX_PROCESSOR_NAME];
MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Get_processor_name(name, &len);
printf("Hello world! I’m %d of %d on %s\n", rank, size, name);
MPI_Finalize();
exit(0);
}
8.3.2.2 Building and Running hello_world
To build and run hello_world.c on a local host, named penguin2 in this example,
perform the following steps:
1. Change to a writable directory.
2. Compile the hello_world executable file:
$ $MPI_ROOT/bin/mpicc -o hello_world $MPI_ROOT/help/hello_world.c
If /opt/hpmpi/bin is in the PATH , as it should be, this command can be simplified to
the following:
$ mpicc -o hello_world $MPI_ROOT/help/hello_world.c
3. Run the hello_world executable file:
$ $MPI_ROOT/bin/mpirun -srun -n4 hello_world
If /opt/hpmpi/bin is in the PATH , this command can be simplified to the following:
$ mpirun -srun -n4 hello_world
In this command, -n4 specifies that the number of processes to run is four, and the
allocated nodes from SLURM are to be used.
4. Analyze hello_world output.
HP-MPI prints the output from running the hello_world executable in nondeterministic
order. The following is an example of the output:
Using HP-MPI 8-3