HelloWorld MPI

README.md

+# MPI LAB
+
+## Prepare your User
+To establish ssh connection between master and slaves without prompt required password we copy
+public id on slave machines as following
+
+```
+$ ssh-keygen (dont use any passphrase)
+$ ssh-copy-id mpiuser@slave1 
+$ ssh-copy-id mpiuser@slave2
+```
+
+## Running MPI programs
+if you want to compile your own code, the name of which let’s say is *mpi_sample.c*, you will compile it
+the way given below, to generate an executable *mpi_sample*.
+```
+mpicc -o mpi_sample mpi_sample.c
+```
+
+**Note**: compile your code within the **/nfs** shared directory
+
+To run it only in your machine (with 2 processes), you do
+```
+mpirun -np 2 ./mpi_sample 
+```
+
+Now, to run it within a cluster (add the hostname of the cluster's node you want to use),
+
+```
+mpirun -np 5 -hosts master,localhost ./mpi_sample
+```
+
+Or specify the same in a hostfile 
+
+```
+mpirun -np 3 -f mpi_hosts ./mpi_sampl
+```
+
+

hello_world.c

+// An intro MPI hello world program that uses MPI_Init, MPI_Comm_size,
+// MPI_Comm_rank, MPI_Finalize, and MPI_Get_processor_name.
+//
+#include <mpi.h>
+#include <stdio.h>
+
+int main(int argc, char** argv) {
+  // Initialize the MPI environment. The two arguments to MPI Init are not
+  // currently used by MPI implementations, but are there in case future
+  // implementations might need the arguments.
+  MPI_Init(NULL, NULL);
+
+  // Get the number of processes
+  int world_size;
+  MPI_Comm_size(MPI_COMM_WORLD, &world_size);
+
+  // Get the rank of the process
+  int world_rank;
+  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
+
+  // Get the name of the processor
+  char processor_name[MPI_MAX_PROCESSOR_NAME];
+  int name_len;
+  MPI_Get_processor_name(processor_name, &name_len);
+
+  // Print off a hello world message
+  printf("Hello world from processor %s, rank %d out of %d processors\n",
+         processor_name, world_rank, world_size);
+
+  // Finalize the MPI environment. No more MPI calls can be made after this
+  MPI_Finalize();
+}
\ No newline at end of file

mpi_hosts

+master
+slave1
+slave2