HP XC System 2.x Software manual Example Application helloworld, Building and Running helloworld

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, -n4specifies 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