NAG Library Manual, Mark 27.2
```/* nag_lapacklin_dgecon (f07agc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.2, 2021.
*/

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

int main(void) {

/* Scalars */
double anorm, rcond;
Integer exit_status = 0;
Integer i, ipiv_len, j, n, pda;
NagError fail;
Nag_OrderType order;

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

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

INIT_FAIL(fail);

printf("nag_lapacklin_dgecon (f07agc) Example Program Results\n");
/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%" NAG_IFMT "%*[^\n] ", &n);
pda = n;
ipiv_len = n;

/* Allocate memory */
if (!(a = NAG_ALLOC(n * n, double)) ||
!(ipiv = NAG_ALLOC(ipiv_len, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

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

/* Compute norm of A */
/* nag_blast_dge_norm (f16rac).
* 1-norm, infinity-norm, Frobenius norm, largest absolute
* element, real general matrix
*/
nag_blast_dge_norm(order, Nag_OneNorm, n, n, a, pda, &anorm, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_blast_dge_norm (f16rac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* 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;
}

printf("\n");
/* Estimate condition number */
/* nag_lapacklin_dgecon (f07agc).
* Estimate condition number of real matrix, matrix already
*/
nag_lapacklin_dgecon(order, Nag_OneNorm, n, a, pda, anorm, &rcond, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgecon (f07agc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* nag_machine_precision (x02ajc).
* The machine precision
*/
if (rcond >= nag_machine_precision) {
printf("Estimate of condition number =%11.2e\n", 1.0 / rcond);
} else
printf("A is singular to working precision\n");
END:
NAG_FREE(a);
NAG_FREE(ipiv);
return exit_status;
}
```