NAG Library Manual, Mark 27.3
```/* nag_lapacklin_zgtsvx (f07cpc) Example Program.
*
* Copyright 2021 Numerical Algorithms Group.
*
* Mark 27.3, 2021.
*/

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

int main(void) {

/* Scalars */
double rcond;
Integer exit_status = 0, i, j, n, nrhs, pdb, pdx;

/* Arrays */
Complex *b = 0, *d = 0, *df = 0, *dl = 0, *dlf = 0, *du = 0, *du2 = 0;
Complex *duf = 0, *x = 0;
double *berr = 0, *ferr = 0;
Integer *ipiv = 0;

/* Nag Types */
NagError fail;
Nag_OrderType order;

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

printf("nag_lapacklin_zgtsvx (f07cpc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &n, &nrhs);
if (n < 0 || nrhs < 0) {
printf("Invalid n or nrhs\n");
exit_status = 1;
goto END;
}
/* Allocate memory */
if (!(b = NAG_ALLOC(n * nrhs, Complex)) || !(d = NAG_ALLOC(n, Complex)) ||
!(df = NAG_ALLOC(n, Complex)) || !(dl = NAG_ALLOC(n - 1, Complex)) ||
!(dlf = NAG_ALLOC(n - 1, Complex)) || !(du = NAG_ALLOC(n - 1, Complex)) ||
!(du2 = NAG_ALLOC(n - 2, Complex)) ||
!(duf = NAG_ALLOC(n - 1, Complex)) ||
!(x = NAG_ALLOC(n * nrhs, Complex)) ||
!(berr = NAG_ALLOC(nrhs, double)) || !(ferr = NAG_ALLOC(nrhs, double)) ||
!(ipiv = NAG_ALLOC(n, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

#ifdef NAG_COLUMN_MAJOR
pdb = n;
pdx = n;
#else
pdb = nrhs;
pdx = nrhs;
#endif

/* Read the tridiagonal matrix A from data file */
for (i = 0; i < n - 1; ++i)
scanf(" ( %lf , %lf )", &du[i].re, &du[i].im);
scanf("%*[^\n]");
for (i = 0; i < n; ++i)
scanf(" ( %lf , %lf )", &d[i].re, &d[i].im);
scanf("%*[^\n]");
for (i = 0; i < n - 1; ++i)
scanf(" ( %lf , %lf )", &dl[i].re, &dl[i].im);
scanf("%*[^\n]");

/* Read the right hand matrix B */
for (i = 1; i <= n; ++i)
for (j = 1; j <= nrhs; ++j)
scanf(" ( %lf , %lf )", &B(i, j).re, &B(i, j).im);
scanf("%*[^\n]");

/* Solve the equations AX = B using nag_lapacklin_zgtsvx (f07cpc). */
nag_lapacklin_zgtsvx(order, Nag_NotFactored, Nag_NoTrans, n, nrhs, dl, d, du,
dlf, df, duf, du2, ipiv, b, pdb, x, pdx, &rcond, ferr,
berr, &fail);
if (fail.code != NE_NOERROR && fail.code != NE_SINGULAR) {
printf("Error from nag_lapacklin_zgtsvx (f07cpc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Print solution using nag_file_print_matrix_complex_gen_comp (x04dbc). */
fflush(stdout);
nag_file_print_matrix_complex_gen_comp(
order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, nrhs, x, pdx,
Nag_BracketForm, "%7.4f", "Solution(s)", Nag_IntegerLabels, 0,
Nag_IntegerLabels, 0, 80, 0, 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_complex_gen_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print solution, error bounds and condition number */
printf("\nBackward errors (machine-dependent)\n");
for (j = 0; j < nrhs; ++j)
printf("%11.1e%s", berr[j], j % 7 == 6 ? "\n" : " ");

printf("\n\nEstimated forward error bounds (machine-dependent)\n");
for (j = 0; j < nrhs; ++j)
printf("%11.1e%s", ferr[j], j % 7 == 6 ? "\n" : " ");

printf("\n\nEstimate of reciprocal condition number\n%11.1e\n", rcond);
if (fail.code == NE_SINGULAR)
printf("Error from nag_lapacklin_zgtsvx (f07cpc).\n%s\n", fail.message);
END:
NAG_FREE(b);
NAG_FREE(d);
NAG_FREE(df);
NAG_FREE(dl);
NAG_FREE(dlf);
NAG_FREE(du);
NAG_FREE(du2);
NAG_FREE(duf);
NAG_FREE(x);
NAG_FREE(berr);
NAG_FREE(ferr);
NAG_FREE(ipiv);

return exit_status;
}

#undef B
```