```/* nag_dtrexc (f08qfc) Example Program.
*
* Copyright 2014 Numerical Algorithms Group.
*
* Mark 7, 2001.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf08.h>
#include <nagx04.h>

int main(void)
{
/* Scalars */
Integer       i, ifst, ilst, j, n, pdq, pdt;
Integer       exit_status = 0;
NagError      fail;
Nag_OrderType order;
/* Arrays */
double        *q = 0, *t = 0;

#ifdef NAG_COLUMN_MAJOR
#define T(I, J) t[(J-1)*pdt + I - 1]
order = Nag_ColMajor;
#else
#define T(I, J) t[(I-1)*pdt + J - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

printf("nag_dtrexc (f08qfc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
scanf("%ld%*[^\n] ", &n);
#ifdef NAG_COLUMN_MAJOR
pdq = 1;
pdt = n;
#else
pdq = 1;
pdt = n;
#endif

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

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

/* Reorder the Schur factorization T */
/* nag_dtrexc (f08qfc).
* Reorder Schur factorization of real matrix using
* orthogonal similarity transformation
*/
nag_dtrexc(order, Nag_NotQ, n, t, pdt, q, pdq, &ifst, &ilst, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_dtrexc (f08qfc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Print reordered Schur form */
/* nag_gen_real_mat_print (x04cac).
* Print real general matrix (easy-to-use)
*/
fflush(stdout);
nag_gen_real_mat_print(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, n,
t, pdt, "Reordered Schur form", 0, &fail);
if (fail.code != NE_NOERROR)
{
printf("Error from nag_gen_real_mat_print (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
END:
NAG_FREE(q);
NAG_FREE(t);

return exit_status;
}
```