Main Code

static char help[] = "Introduction to the Sparse Matrix environment.\n\n";


#include "petsc.h"
#include <stdlib.h>

#define     NR  5
#define     NC  8


int main(int argc, char *argv[])
{
    PetscInt    i,j,nr=NR,nc=NC,idxm[NR],idxn[NC],high,low;
    PetscInt    rank,size;
    Mat         A;/*This is going to be the main working matrix of the tutorial.*/
    PetscScalar values[NR*NC];
    PetscInt    *d_nnz,*o_nnz;

    PetscInitialize(&argc,&argv,(char*)0,help);

    MPI_Comm_size(PETSC_COMM_WORLD,&size);
    MPI_Comm_rank(PETSC_COMM_WORLD,&rank);

    /**************************************************************************
    *          Setting Up the Layout and the type of the  Matrix              *
    **************************************************************************/

    MatCreate(PETSC_COMM_WORLD,&A);
    MatSetSizes(A,PETSC_DECIDE,PETSC_DECIDE,nr,nc);
    MatSetType(A,MATMPIAIJ);
    MatSetFromOptions(A);

    MatSetUp(A);
    MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);/*Starting the Matrxi Assembly*/
    MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

    MatGetOwnershipRange(A,&low,&high);




    /**************************************************************************
    *                     Setting the Values of the Matrix                    *
    **************************************************************************/


    PetscMalloc((high-low)*sizeof(PetscInt),&d_nnz);
    PetscMalloc((high-low)*sizeof(PetscInt),&o_nnz);
    for(i=0;i<nc;i++)
    {
        idxn[i]=i;
    }
    for(i=low;i<high;i++)
    {
        idxm[i-low]=i;
    }

    printf("Low %d High %d\n",low,high);

    for(i=low;i<high;i++)
    {
        d_nnz[i-low]=0;
        o_nnz[i-low]=0;
        for(j=0;j<nc;j++)
        {
            if((j-i<=3) && (j>=i))
                values[(i-low)*nc+j]=1;
            else
                values[(i-low)*nc+j]=0;
            if(values[(i-low)*nc+j]!=0)
            {
                if((j>=low)&&(j<high))
                    d_nnz[i-low]++;
                else
                    o_nnz[i-low]++;
            }
        }
    }

    PetscBarrier(PETSC_NULL);/*Just introducing a barrier so that all the processes are to the same level*/


    for(i=low;i<high;i++)
    {
        PetscSynchronizedPrintf(PETSC_COMM_SELF,"Proc: %d o_nnz[%d] %d d_nnz[%d] %d\n",rank,i-low,o_nnz[i-low],i-low,d_nnz[i-low]);
    }

    MatMPIAIJSetPreallocation(A,0,d_nnz,0,o_nnz);

    MatSetValues(A,(high-low),idxm,nc,idxn,values,INSERT_VALUES);/*Setting the value for the assigned idxm[] and idxn[]*/

    MatAssemblyBegin(A,MAT_FINAL_ASSEMBLY);/*Starting the Matrix Assembly*/
    MatAssemblyEnd(A,MAT_FINAL_ASSEMBLY);

    MatView(A,PETSC_VIEWER_STDOUT_WORLD);/*For checking the value assigned to the matrix A*/
    /**************************************************************************
    *                     Getting the Values of the Matrix                    *
    **************************************************************************/

    for(i=0;i<nc;i++)
    {
        idxn[i]=i;
    }
    for(i=low;i<high;i++)
    {
        idxm[i-low]=i;
    }

    PetscScalar Result[(high-low)*nc];

    MatGetValues(A,(high-low),idxm,nc,idxn,Result);

    PetscBarrier(PETSC_NULL);/*Just introducing a barrier so that all the processes are to the same level*/
    for(i=low;i<high;i++)
    {
        for(j=0;j<nc;j++)
        {
            PetscSynchronizedPrintf(PETSC_COMM_SELF,"%.2f\t",Result[(i-low)*nc+j]);
        }
        PetscSynchronizedPrintf(PETSC_COMM_SELF,"\n");
    }

    //PetscPrintf(PETSC_COMM_SELF,"The local matrix size for the process %d is %d cross %d\n",rank+1,M,N);
    //PetscPrintf(PETSC_COMM_SELF,"The local matrix size for the process %d is %d to %d\n",rank+1,low,high);

    MatDestroy(&A);

    PetscFinalize();

    return 0;
}