PETSc Matrix Doubt

    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;
    }

    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*/

    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*/