```/* nag_zgtrfs (f07cvc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.2, 2017.
*/
#include <stdio.h>
#include <nag.h>
#include <nagx04.h>
#include <nag_stdlib.h>
#include <nagf07.h>
#include <nagf16.h>

int main(void)
{
/* Scalars */
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, *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_zgtrfs (f07cvc) 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;
}

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]");

/* Copy A into duf, df and dlf */
for (i = 0; i < n - 1; ++i) {
duf[i].re = du[i].re, duf[i].im = du[i].im;
df[i].re = d[i].re, df[i].im = d[i].im;
dlf[i].re = dl[i].re, dlf[i].im = dl[i].im;
}
df[n - 1].re = d[n - 1].re, df[n - 1].im = d[n - 1].im;

/* copy B into X using nag_zge_copy (f16tfc). */
nag_zge_copy(order, Nag_NoTrans, n, nrhs, b, pdb, x, pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zge_copy (f16tfc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Factorize the copy of the tridiagonal matrix A using
* nag_zgttrf (f07crc).
*/
nag_zgttrf(n, dlf, df, duf, du2, ipiv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zgttrf (f07crc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* Solve the equations AX = B using nag_zgttrs (f07csc). */
nag_zgttrs(order, Nag_NoTrans, n, nrhs, dlf, df, duf, du2, ipiv, x,
pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zgttrs (f07csc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Improve the solution and compute error estimates using
* nag_zgtrfs (f07cvc).
*/
nag_zgtrfs(order, Nag_NoTrans, n, nrhs, dl, d, du, dlf, df, duf, du2,
ipiv, b, pdb, x, pdx, ferr, berr, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_zgtrfs (f07cvc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the solution using nag_gen_complx_mat_print_comp (x04dbc). */
fflush(stdout);
nag_gen_complx_mat_print_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_gen_complx_mat_print_comp (x04dbc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* Print the forward and backward error estimates */
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");
END:
NAG_FREE(b);
NAG_FREE(berr);
NAG_FREE(d);
NAG_FREE(df);
NAG_FREE(dl);
NAG_FREE(dlf);
NAG_FREE(du);
NAG_FREE(du2);
NAG_FREE(duf);
NAG_FREE(ferr);
NAG_FREE(x);
NAG_FREE(ipiv);

return exit_status;
}

#undef B
```