clapack_dgesv test

gesv_test.c

#include <atlas/clapack.h>
#include <stdio.h>

int main() {
  double a[9] = { 1,0,0,
                 -1,0,1,
                  2,1,1};
  double b[6] = {1,0,
                 1,2,
                 4,2};

  int n = 3;
  int nrhs = 2;
  int ipiv[3];

  clapack_dgesv(CblasRowMajor, n, nrhs, a, n, ipiv, b, n);

  int i,j;
  for (i=0; i<n; i++) {
    for (j=0; j<nrhs; j++) {
      printf("%f ",b[j+i*nrhs]);
    }
    printf("\n");
  }
  printf("\n");

  /*
   b should be equal to:
   1 0
   0 0
   2 2
   but is actually equal to:
   1 -2
   1 2
   -8 6
   */

  //try again with b stored in column-major form
  double a2[9] = { 1,0,0,
                 -1,0,1,
                  2,1,1};
  double bt[6] = {1,1,4,0,2,2};

  clapack_dgesv(CblasRowMajor, n, nrhs, a2, n, ipiv, bt, n);

  //column-major print
  for (i=0; i<n; i++) {
    for (j=0; j<nrhs; j++) {
      printf("%f ",bt[i+j*n]);
    }
    printf("\n");
  }
  //this time it gives the correct answer

  return 0;
}