```/* nag_lapacklin_dgtrfs (f07chc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/

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

int main(void)
{
/* Scalars */
Integer exit_status = 0, i, j, n, nrhs, pdb, pdx;

/* Arrays */
double *b = 0, *berr = 0, *d = 0, *df = 0, *dl = 0, *dlf = 0, *du = 0;
double *du2 = 0, *duf = 0, *ferr = 0, *x = 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_dgtrfs (f07chc) 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, double)) ||
!(berr = NAG_ALLOC(nrhs, double)) ||
!(d = NAG_ALLOC(n, double)) ||
!(df = NAG_ALLOC(n, double)) ||
!(dl = NAG_ALLOC(n - 1, double)) ||
!(dlf = NAG_ALLOC(n - 1, double)) ||
!(du = NAG_ALLOC(n - 1, double)) ||
!(du2 = NAG_ALLOC(n - 2, double)) ||
!(duf = NAG_ALLOC(n - 1, double)) ||
!(ferr = NAG_ALLOC(nrhs, double)) ||
!(x = NAG_ALLOC(n * 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", &du[i]);
scanf("%*[^\n]");
for (i = 0; i < n; ++i)
scanf("%lf", &d[i]);
scanf("%*[^\n]");
for (i = 0; i < n - 1; ++i)
scanf("%lf", &dl[i]);
scanf("%*[^\n]");

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

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

/* Copy B into X using nag_blast_dge_copy (f16qfc). */
nag_blast_dge_copy(order, Nag_NoTrans, n, nrhs, b, pdb, x, pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_blast_dge_copy (f16qfc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Factorize the copy of the tridiagonal matrix A
* using nag_lapacklin_dgttrf (f07cdc).
*/
nag_lapacklin_dgttrf(n, dlf, df, duf, du2, ipiv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgttrf (f07cdc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Solve the equations AX = B using  nag_lapacklin_dgttrs (f07cec). */
nag_lapacklin_dgttrs(order, Nag_NoTrans, n, nrhs, dlf, df, duf, du2, ipiv, x,
pdx, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_lapacklin_dgttrs (f07cec).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Improve the solution and compute error estimates using
* nag_lapacklin_dgtrfs (f07chc).
*/
nag_lapacklin_dgtrfs(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_lapacklin_dgtrfs (f07chc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print the solution using nag_file_print_matrix_real_gen (x04cac). */
fflush(stdout);
nag_file_print_matrix_real_gen(order, Nag_GeneralMatrix, Nag_NonUnitDiag, n, nrhs,
x, pdx, "Solution(s)", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\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
```