NAG Library Manual, Mark 29.2
```/* nag_lapacklin_dgetrs (f07aec) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.2, 2023.
*/

#include <nag.h>
#include <stdio.h>

int main(void) {
/* Scalars */
Integer i, j, n, nrhs, pda, pdb;
Integer exit_status = 0;
NagError fail;
Nag_OrderType order;

/* Arrays */
double *a = 0, *b = 0;
Integer *ipiv = 0;

#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J - 1) * pda + I - 1]
#define B(I, J) b[(J - 1) * pdb + I - 1]
order = Nag_ColMajor;
#else
#define A(I, J) a[(I - 1) * pda + J - 1]
#define B(I, J) b[(I - 1) * pdb + J - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_lapacklin_dgetrs (f07aec) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &n, &nrhs);

/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, double)) || !(b = NAG_ALLOC(n * nrhs, double)) ||
!(ipiv = NAG_ALLOC(n, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
#ifdef NAG_COLUMN_MAJOR
pda = n;
pdb = n;
#else
pda = n;
pdb = nrhs;
#endif

/* Read A and B from data file */
for (i = 1; i <= n; ++i) {
for (j = 1; j <= n; ++j)
scanf("%lf", &A(i, j));
}
scanf("%*[^\n] ");
for (i = 1; i <= n; ++i) {
for (j = 1; j <= nrhs; ++j)
scanf("%lf", &B(i, j));
}
scanf("%*[^\n] ");

/* Factorize A */
* LU factorization of real m by n matrix
*/
nag_lapacklin_dgetrf(order, n, n, a, pda, ipiv, &fail);
if (fail.code != NE_NOERROR) {
exit_status = 1;
goto END;
}

/* Compute solution */
/* nag_lapacklin_dgetrs (f07aec).
* Solution of real system of linear equations, multiple
* right-hand sides, matrix already factorized by nag_lapacklin_dgetrf
*/
nag_lapacklin_dgetrs(order, Nag_NoTrans, n, nrhs, a, pda, ipiv, b, pdb,
&fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgetrs (f07aec).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print solution */
/* nag_file_print_matrix_real_gen (x04cac).
* Print real general matrix (easy-to-use)
*/
fflush(stdout);
nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n,
nrhs, b, pdb, "Solution(s)", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(a);
NAG_FREE(b);
NAG_FREE(ipiv);
return exit_status;
}
```