Can not get the simple ScaLAPACK code to work

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Can not get the simple ScaLAPACK code to work

Postby Looser » Tue Aug 22, 2006 3:32 am


I'm new to ScaLAPACK and not a very good programmer either. What I am trying to do is to get a very simple program to solve an equation system and when it works I intend to make it more sophisticated so I can easily use it for large matrices.

However, I am trying to do this in C, which has turned out to be an mistake. I have spent more than a months work on this code and it is still not working.

When running the program I get: "On entry to PDGETRF parameter number 4 had an illegal value"

I have tried a lot of different ways with this and I still can not get it to work. I would be very grateful if someone with more skill and experience than me could have a look at the code and advice how to make it work.


* This function solves an equation of the A*x=b type, where x and b are
* vectors and A is a matrix.

#include <stdio.h>
#include <math.h> /* sqrt() */
#include <mpi.h>
#include <stdlib.h>
/*int MPI_Init(int *argc, char ***argv);*/

int Get_dimension(int order, int block_size, int my_process_row_or_col,
int nproc_rows_or_cols);
void Build_descrip(int my_rank, int* descrip,
int m, int n, int row_block_size,
int col_block_size, int blacs_grid,
int leading_dim);

extern void descinit_(int* descrip, int* m, int* n,
int* row_block_size, int* col_block_size,
int* first_proc_row, int* first_proc_col,
int* blacs_grid, int* leading_dim,
int* error_info);

int main(int argc, char *argv[])
/* Declare variables */

double subgrid; /* one-element subgrid on each process */
double norm; /* result: value of 2-norm */
int s[9]; /* ScaLAPACK descriptor */
int me, nprocs, icontxt, x, y;
char grid_major = 'R';
int ix = 1, jx = 1, mx = 1; /* some striding info for ScaLAPACK call */

int NoOfRows; /* No of rows of processor matrix */
int NoOfCol; /* No of columns of processor matrix */

int desc_A[9]; /* Scalapack descriptor matrix A */
int desc_b[9]; /* Scalapack descriptor vector b */
int desc_x[9]; /* Scalapack descriptor vector x */

double *A_loc; /* Matrix A local portion */
double *b_loc; /* Vector b local portion */

int n=8; /* Square dimension of matrix A */
int BlockSize; /* Size of local data block */

int mloc_A; /* No of rows in local data block */
int nloc_A; /* No of columns in local data block */
int mloc_b; /* No of rows in local data block */
int nloc_b; /* No of columns in local data block */

int MyRow; /* Local process row number */
int MyCol; /* Local process column number */

int nbuser=64; /* Maximal array size */
int info; /* Error flag */

int i_loc; /* Local row index */
int j_loc; /* Local column index */

int i_glob; /* Global row index */
int j_glob; /* Global column index */

int intdummy;
int intdummy2;
int* intdummypek;
int * ipvt;
double doubledummy;
/* double doubledummy; */
char chardummy;
const int zero=0;
const int one=1;
int error_info;

/* Initialization */

MPI_Init(&argc, &argv);
MPI_Comm_rank(MPI_COMM_WORLD, &me);
MPI_Comm_size(MPI_COMM_WORLD, &nprocs);

/* Create processor grid */

* Cblacs_pinfo initializes BLACS; standard BLACS + ScaLAPACK procedure
/* Determine total no of processors */
Cblacs_pinfo(&me, &nprocs);

/* Factor the number of processors into a rectangle
-quadratic shape preferred */

for (x=1; x<= 10000; x++){
if ((x*x) >= nprocs) {
if ((x*x) == nprocs){
NoOfCol =x;
} /* endif */
else {
for (y=x; y>=1; y--){
if (x*y==nprocs){
} /* endif */
} /* endfor */
} /* endelse */
} /* endif */
} /* endfor */

/* Inform Blacs of this grid extent */
Cblacs_get(0, 0, &icontxt);

/* initialize BLACS grid and get BLACS context */
Cblacs_gridinit(&icontxt, &grid_major, NoOfRows, NoOfCol);

/* Get process coordinates in processor grid */
Cblacs_pcoord(icontxt, me, &MyRow, &MyCol);

/* Determine a good block size */
if ((n/NoOfRows)<(n/NoOfCol))
if (nbuser>0){
if (BlockSize>nbuser)
if (BlockSize<1)

/* Create a Scalapack array descriptor and allocate memory on each process*/
mloc_A=Get_dimension(n, BlockSize, MyRow, NoOfRows);
nloc_A=Get_dimension(n, BlockSize, MyCol, NoOfCol);
mloc_b=Get_dimension(n, BlockSize, MyRow, NoOfRows);
nloc_b=Get_dimension(1, BlockSize, MyCol, NoOfCol);

descinit_(desc_A, &n, &n, &BlockSize, &BlockSize, &intdummy2, &intdummy2, &icontxt, &mloc_A, &error_info);

descinit_(desc_b, &intdummy, &n, &BlockSize, &intdummy, &intdummy2, &intdummy2, &icontxt, &mloc_b, &error_info);

/* int ipvt[mloc_A];*/ /* Pivoting information */
ipvt = (int*)malloc(mloc_A*sizeof(int));

/* Allocate space for each process */
A_loc = (double*) malloc((mloc_A*nloc_A)*sizeof(double));
b_loc = (double*) malloc((mloc_b*nloc_b)*sizeof(double));

/* Initialize*/

for(j_loc=0; j_loc<nloc_A; j_loc++){
j_glob=indxl2g_(&j_loc, &BlockSize, &MyCol, &zero, &NoOfCol);
for(i_loc=0; i_loc<mloc_A; i_loc++){
i_glob=indxl2g_(&i_loc, &BlockSize, &MyRow, &zero, &NoOfRows);
A_loc[i_loc, j_loc]=((double)(1.0+sqrt(fabs(i_glob-j_glob)/8)));

for(j_loc=0; j_loc<nloc_b; j_loc++){
j_glob=indxl2g_(&j_loc, &one, &MyCol, &zero, &NoOfCol);
for(i_loc=0; i_loc<mloc_b; i_loc++){
i_glob=indxl2g_(&i_loc, &BlockSize, &MyRow, &zero, &NoOfRows);

intdummy=indxl2g_(&one, &BlockSize, &MyRow, &zero, &nprocs);
intdummy2=indxl2g_(&one, &BlockSize, &MyCol, &zero, &nprocs);

/* Solve the equation */
Cblacs_barrier(icontxt, "A");

pdgetrf_(&mloc_A, &nloc_A, (double *)A_loc, &intdummy, &intdummy2, desc_A, &ipvt, &info);

if (info!=0)
printf("\n Error i pdgetrf, ERROR=%i\n", info);

chardummy='N'; intdummy=1; intdummy2=0;
pdgetrs_(&chardummy, &n, &intdummy, A_loc, &intdummy, &intdummy, desc_A, &ipvt,
b_loc, &intdummy, &intdummy, desc_b, &info);

if (info!=0)
printf("\n Error in pdgetrs");

free (A_loc); /* Free allocated heap memory for each process */

if (me == 0) {
/* double diff;
diff = norm - (double) nprocs;
if ( diff > -0.01 && diff < 0.01 ) {
} else {
printf("ScaLAPACKmkI example FAILED. ");
} */

/* MPI Collect data f(b_loc) from all processes to give the global X-vector */

free (b_loc); /* Free allocated heap memory for each process */


return (0);

* Simplified wrapper for ScaLAPACK routine numroc
* numroc computes minimum number of rows or columns needed to store
* a process' piece of a distributed array
int Get_dimension(int order, int block_size, int my_process_row_or_col,
int nproc_rows_or_cols) {

int first_process_row_or_col = 0; /* Assume array begins in row */
/* or column 0. */
int return_val;

extern int numroc_(int* order, int* block_size,
int* my_process_row_or_col, int* first_process_row_or_col,
int* nproc_rows_or_cols);

return_val = numroc_(&order, &block_size, &my_process_row_or_col,
&first_process_row_or_col, &nproc_rows_or_cols);
return return_val;
} /* Get_dimension */

/* end file */
Posts: 2
Joined: Tue Aug 22, 2006 2:39 am

Postby Julie » Tue Aug 22, 2006 12:42 pm

Hi Theo,

I did not try to run your code but here are some remarks from a quick overlook:
    1. Your call to pdgetrf is not correct. IA, JA need to be the global coordinates where the matrix starts. Global implies in particular that
    they NEED to be the same on all the processes. I think you are trying to give to ScaLAPACK the global position of the local coordinates where each local matrix starts in the global matrix.
    Something like that, no? So anyhow, no, this is not it. You need to give the global position where the elements (1,1) of the matrix you want to work on is located in the array A.
    Yes this can appear as weird,
    for most of users, this will simply be (1,1). So my advice is to set IA=1 and JA=1 (yep as simple as this...). Why IA and JA in the interface?
    IA and JA are very useful when you want to work on submatrices. But if you just want to work on the one big matrix, you should not care too much about them.

    2- Your code is a good attempt. You can find another example at: . Maybe have a look at it.

Posts: 299
Joined: Wed Feb 23, 2005 12:32 am
Location: ICL, Denver. Colorado


Postby Looser » Thu Aug 24, 2006 1:57 am

Thanks Julie!

I really appriciate you taking the time to help me. Thanks again!

Posts: 2
Joined: Tue Aug 22, 2006 2:39 am

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