NAG Library Manual, Mark 30.1
```/* nag_lapackeig_ztgexc (f08ytc) Example Program.
*
* Copyright 2024 Numerical Algorithms Group.
*
* Mark 30.1, 2024.
*/

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

int main(void) {
/* Scalars */
Integer i, ifst, ilst, j, n, pdq, pds, pdt, pdz;
Integer exit_status = 0;

/* Arrays */
Complex *q = 0, *s = 0, *t = 0, *z = 0;
char nag_enum_arg[40];

NagError fail;
Nag_OrderType order;
Nag_Boolean wantq, wantz;
Nag_MatrixType upmat = Nag_UpperMatrix;
Nag_DiagType diag = Nag_NonUnitDiag;
Nag_LabelType intlab = Nag_IntegerLabels;
Nag_ComplexFormType brac = Nag_BracketForm;

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

INIT_FAIL(fail);

printf("nag_lapackeig_ztgexc (f08ytc) Example Program Results\n\n");

/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
if (n < 0) {
printf("Invalid n\n");
exit_status = 1;
goto END;
}
scanf(" %39s%*[^\n]", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
wantq = (Nag_Boolean)nag_enum_name_to_value(nag_enum_arg);
scanf(" %39s%*[^\n]", nag_enum_arg);
wantz = (Nag_Boolean)nag_enum_name_to_value(nag_enum_arg);

pds = n;
pdt = n;
pdq = (wantq ? n : 1);
pdz = (wantz ? n : 1);

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

/* Read S and T from data file */
for (i = 1; i <= n; ++i)
for (j = 1; j <= n; ++j)
scanf(" ( %lf , %lf )", &S(i, j).re, &S(i, j).im);
scanf("%*[^\n]");
for (i = 1; i <= n; ++i)
for (j = 1; j <= n; ++j)
scanf(" ( %lf , %lf )", &T(i, j).re, &T(i, j).im);
scanf("%*[^\n]");

/* Read the row indices */
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &ifst, &ilst);

/* Reorder the S and T */
nag_lapackeig_ztgexc(order, wantq, wantz, n, s, pds, t, pdt, q, pdq, z, pdz,
ifst, &ilst, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapackeig_ztgexc (f08ytc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print reordered generalized Schur form */
fflush(stdout);
nag_file_print_matrix_complex_gen_comp(order, upmat, diag, n, n, s, pds, brac,
"%7.4f", "Reordered Schur matrix S",
intlab, NULL, intlab, NULL, 80, 0,
NULL, &fail);
if (fail.code != NE_NOERROR)
goto PRERR;
printf("\n");
fflush(stdout);
nag_file_print_matrix_complex_gen_comp(order, upmat, diag, n, n, t, pdt, brac,
"%7.4f", "Reordered Schur matrix T",
intlab, NULL, intlab, NULL, 80, 0,
NULL, &fail);
PRERR:
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_complex_gen_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
}

END:
NAG_FREE(q);
NAG_FREE(s);
NAG_FREE(t);
NAG_FREE(z);

return exit_status;
}
```