pajayrao/mpi installation on ubuntu with basic mpi programs.md

## mpi installation on ubuntu with basic mpi programs.md

      
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              mpi installation on ubuntu with basic mpi programs.md
            
          
    Installing and Basic Programs on MPI C

Installing MPI on Ubuntu

Run the following command on terminal
$ sudo apt-get install libcr-dev mpich2 mpich2-doc

Compiling MPI Programs

mpicc -o hello_world_c hello_world.c

Executing MPI Programs

mpiexec -np 4 ./hello_world_c


-np : Number of Processes

Basic MPI Programs


Basic MPI Function


*MPI_Init(&argc,&argv) : Initialize MPI part of the program. Compulsory for all MPI programs.


*MPI_Comm_rank(MPI_COMM_WORLD,&rank) : Returns the rank (process id) of that processes.


*MPI_Comm_size(MPI_COMM_WORLD,&size): Returns the total number of processes.


*MPI_Recv(void *buf, int count, MPI_Datatype datatype, int source, int tag,MPI_Comm comm, MPI_Status *status):Recieves data from specified rank.


*MPI_Send(const void *buf, int count, MPI_Datatype datatype, int dest, int tag,MPI_Comm comm) : Sends data to the specified rank.


*MPI_Scatter(void *send_data,int send_count,MPI_Datatype send_datatype,void *recv_data,int recv_count,MPI_Datatype recv_datatype,int root,MPI_Comm communicator) : Scatters data from a specified rank accross all the processes.


*MPI_Gather(void *send_data,int send_count,MPI_Datatype send_datatype,void *recv_data,int recv_count,MPI_Datatype recv_datatype,int root, MPI_Comm communicator) : Gathers data from all process to the specified process.


*MPI_Reduce(const void *sendbuf, void *recvbuf, int count, MPI_Datatype datatype,MPI_Op op, int root, MPI_Comm comm) :Reduces the specified a array by a specific operation accross all processes.

1. MPI Program to send data from 3 process to the fourth process

#include<mpi.h>
#include<stdio.h>
int main(int argc,char **argv)
{
	int rank,size;
	char A[3][50]={"RVCE","COLLEGE","SIDDA"};
	char B[50]={},C[50]={},D[50]={};
	MPI_Init(&argc,&argv);
	MPI_Comm_rank(MPI_COMM_WORLD,&rank);
	MPI_Comm_size(MPI_COMM_WORLD,&size);
	if(rank==0)
	{
	printf("Rank %d started \n",rank);
	
	MPI_Recv(B,50,MPI_CHAR,1,0,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
	printf("Rank %d recieve %s message \n",1,B);
	MPI_Recv(C,50,MPI_CHAR,2,0,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
	printf("Rank %d recieve %s message \n",2,C);
	MPI_Recv(D,50,MPI_CHAR,3,0,MPI_COMM_WORLD,MPI_STATUS_IGNORE);
	printf("Rank %d recieve %s message \n",3,D);
	

	}
	else
	{
	printf("Rank %d sends %s message \n",rank,A[rank-1]);
	MPI_Send(A[rank-1],20,MPI_CHAR,0,0,MPI_COMM_WORLD);
	
	}
MPI_Finalize();

	
}

2. MPI Program to calculate value of PI using Monte Carlo method

#include<stdio.h>
#include<mpi.h>
#include<stdlib.h>
#include <time.h>
int main(int argc,char **argv)
{
	int rank,size,i;
	double x=0,y=0,pi,z;
	int no = atoi(argv[1]);
	int count=0,total_count=0,no_div=0,fin_no = 0;
	MPI_Init(&argc,&argv);
	MPI_Comm_rank(MPI_COMM_WORLD,&rank);
	MPI_Comm_size(MPI_COMM_WORLD,&size);
	no_div = no/size;
	srand ( time(NULL) );
	for(i=0;i<no_div;i++)
		{
		
		x=(rand()%100)/(double)100;
		y=(rand()%100)/(double)100;
		z=x*x+y*y;
		if(z<=1)
			count++;

		}
	printf("For rank %d count = %d itrr = %d\n",rank,count,no_div);
	MPI_Reduce(&count,&total_count,1,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
	MPI_Reduce(&no_div,&fin_no,1,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
	
	if(rank ==0)
		{
	printf("Total count  = %d, total itrr = %d\n",total_count,fin_no);
	pi = ((double)total_count)/fin_no*4.0000;


	printf("Pi value = %lf",pi);


		}
	MPI_Finalize();

	
}

3. MPI Program to find sum of 2 large array

#include<mpi.h>
#include<stdio.h>
#include<stdlib.h>
void allocate(int a[],int n)
{
	int i;
	for(i=0;i<n;i++)
		a[i]=rand()%50;

}

int main(int argc, char**argv)
{
int rank,size,n,count,*a=NULL,*b=NULL,*c=NULL,*d=NULL,*e=NULL,*f=NULL,i;

MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&size);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
n=atoi(argv[1]);
printf("Rank =%d n= %d",rank,n);
count=n/size;

d=(int*)malloc(count*sizeof(int));
e=(int*)malloc(count*sizeof(int));
f=(int*)malloc(count*sizeof(int));

if(rank ==0)
	{
	a=(int*)malloc(n*sizeof(int));
	b=(int*)malloc(n*sizeof(int));
	c=(int*)malloc(n*sizeof(int));
	allocate(a,n);
	allocate(b,n);	

}

MPI_Scatter(a,count,MPI_INT,d,count,MPI_INT,0,MPI_COMM_WORLD);
MPI_Scatter(b,count,MPI_INT,e,count,MPI_INT,0,MPI_COMM_WORLD);

for(i=0;i<count;i++)
	f[i]=d[i]+e[i];

MPI_Gather(f,count,MPI_INT,c,count,MPI_INT,0,MPI_COMM_WORLD);
if(rank ==0)
{
for(i=0;i<n;i++)
	printf("%d + %d = %d \n",a[i],b[i],c[i]);
}
MPI_Finalize();


}

References


http://mpitutorial.com/tutorials/mpi-scatter-gather-and-allgather/
https://github.com/nowke/hpc_lab/tree/master/10_mpi_routines