P?POTRF

    int izero=0;
    int ione=1;
    int myrank_mpi, nprocs_mpi;
    MPI_Init( &argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &myrank_mpi);
    MPI_Comm_size(MPI_COMM_WORLD, &nprocs_mpi);
 
    int n = 8;       // (Global) Matrix size
    int nprow = 2;   // Number of row procs
    int npcol = 2;   // Number of column procs
    int nb = 4;      // (Global) Block size
    char uplo='L';   // Matrix is lower triangular
    char layout='R'; // Block cyclic, Row major processor mapping
    
    printf("Usage: ./test matrix_size block_size nprocs_row nprocs_col\n");
 
    if(argc > 1) {
        n = atoi(argv[1]);
    }
    if(argc > 2) {
        nb = atoi(argv[2]);
    }
    if(argc > 3) {
        nprow = atoi(argv[3]);
    }
    if(argc > 4) {
        npcol = atoi(argv[4]);
    }
 
    assert(nprow * npcol == nprocs_mpi);
 
    // Initialize BLACS
    int iam, nprocs;
    int zero = 0;
    int ictxt, myrow, mycol;
    blacs_pinfo_(&iam, &nprocs) ; // BLACS rank and world size
    blacs_get_(&zero, &zero, &ictxt ); // -> Create context
    blacs_gridinit_(&ictxt, &layout, &nprow, &npcol ); // Context -> Initialize the grid
    blacs_gridinfo_(&ictxt, &nprow, &npcol, &myrow, &mycol ); // Context -> Context grid info (# procs row/col, current procs row/col)
 
    // Compute the size of the local matrices
    int mpA    = numroc_( &n, &nb, &myrow, &izero, &nprow ); // My proc -> row of local A
    int nqA    = numroc_( &n, &nb, &mycol, &izero, &npcol ); // My proc -> col of local A
   
    //allocate and fill the matrices A and B 
    double *A;
    A = (double *)calloc(mpA*nqA,sizeof(double)) ;
    if (A==NULL){ printf("Error of memory allocation A on proc %dx%d\n",myrow,mycol); exit(0); }
    int k = 0;
    for (int j = 0; j < nqA; j++) { // local col
        int l_j = j / nb; // which block
        int x_j = j % nb; // where within that block
        int J   = (l_j * npcol + mycol) * nb + x_j; // global col
        for (int i = 0; i < mpA; i++) { // local row
            int l_i = i / nb; // which block
            int x_i = i % nb; // where within that block
            int I   = (l_i * nprow + myrow) * nb + x_i; // global row
            assert(I < n);
            assert(J < n);
            if(I == J) {
                A[k] = nb * nb;
            } else {
                A[k] = I +  J;
            }
            //printf("%d %d -> %d %d -> %f\n", i, j, I, J, A[k]);
            k++;
        }
    }
 
    //creat descriptor
    int descA[9];
    int info=0;
    int lddA = mpA > 1 ? mpA : 1;
    descinit_( descA,  &n, &n, &nb, &nb, &izero, &izero, &ictxt, &lddA, &info);
    if(info != 0) {
        printf("Error in descinit, info = %d\n", info);
    }
    
    //run pdpotrf_ and time
    double MPIt1 = MPI_Wtime();
    printf("[%dx%d] Starting \n", myrow, mycol);
    pdpotrf_(&uplo, &n, A, &ione, &ione, descA, &info);
    if (info != 0) {
        printf("Error in caculate, info = %d\n", info);
    }
    double MPIt2 = MPI_Wtime();
    //exit and finanlize
    blacs_gridexit_(&ictxt);
    MPI_Finalize();
    return 0;

    /* 
     * Origin A: 
     *  
    *16 1 2 3 4 5 6 7
    *1 16 3 4 5 6 7 8
    *2 3 16 5 6 7 8 9
    *3 4 5 16 7 8 9 10
    *4 5 6 7 16 9 10 11
    *5 6 7 8 9 16 11 12
    *6 7 8 9 10 11 16 13
    *7 8 9 10 11 12 13 16
    */

    
    /*After PDPOTRF: 
    *4.00000 1.00000 2.00000 3.00000 4.00000 5.00000 6.00000 7.00000
    *0.250000 3.99218 3.00000 4.00000 5.00000 6.00000 7.00000 8.00000
    *0.500000 0.720158 3.90274 5.00000 6.00000 7.00000 8.00000 9.00000
    *0.750000 0.954992 1.00884 3.67529 7.00000 8.00000 9.00000 10.0000
    *1.00000 1.18983 1.18971 1.06481 3.32191 9.00000 10.0000 11.0000
    *1.25000 1.42466 1.37058 1.17522 0.955149 2.86983 11.0000 12.0000
    *1.50000 1.65949 1.55145 1.28562 0.996646 0.756689 2.31741 13.0000
    *1.75000 1.89433 1.73232 1.39603 1.03814 0.734271 0.500013 1.59132  
    */