NAG Library Manual, Mark 29
```/* nag_sparse_complex_gen_solve_jacssor (f11dsc) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.0, 2023.
*/
#include <nag.h>
int main(void) {
/* Scalars */
Integer exit_status = 0;
double omega, rnorm, tol;
Integer i, itn, m, maxitn, n, nnz;
/* Arrays */
Complex *a = 0, *b = 0, *x = 0;
Integer *icol = 0, *irow = 0;
char nag_enum_arg[40];
/* NAG types */
Nag_SparseNsym_Method method;
Nag_SparseNsym_PrecType precon;
NagError fail;

INIT_FAIL(fail);

printf(
"nag_sparse_complex_gen_solve_jacssor (f11dsc) Example Program Results\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
scanf("%" NAG_IFMT "%*[^\n]", &nnz);
scanf("%39s%*[^\n]", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
method = (Nag_SparseNsym_Method)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s%*[^\n]", nag_enum_arg);
precon = (Nag_SparseNsym_PrecType)nag_enum_name_to_value(nag_enum_arg);
scanf("%lf%*[^\n]", &omega);
scanf("%" NAG_IFMT "%lf%" NAG_IFMT "%*[^\n]", &m, &tol, &maxitn);
if (!(a = NAG_ALLOC((nnz), Complex)) || !(b = NAG_ALLOC((n), Complex)) ||
!(x = NAG_ALLOC((n), Complex)) || !(icol = NAG_ALLOC((nnz), Integer)) ||
!(irow = NAG_ALLOC((nnz), Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Read the matrix A */
for (i = 0; i < nnz; i++)
scanf(" ( %lf , %lf ) %" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &a[i].re,
&a[i].im, &irow[i], &icol[i]);
/* Read rhs vector b and initial approximate solution x */
for (i = 0; i < n; i++)
scanf(" ( %lf , %lf ) ", &b[i].re, &b[i].im);
scanf("%*[^\n]");
for (i = 0; i < n; i++)
scanf(" ( %lf , %lf ) ", &x[i].re, &x[i].im);

/* solve ax = b */
/* nag_sparse_complex_gen_solve_jacssor (f11dsc).
* Solution of complex sparse non-Hermitian linear system, RGMRES, CGS,
* Bi-CGSTAB or TFQMR method, Jacobi or SSOR preconditioner Black Box.
*/
nag_sparse_complex_gen_solve_jacssor(method, precon, n, nnz, a, irow, icol,
omega, b, m, tol, maxitn, x, &rnorm,
&itn, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_complex_gen_solve_jacssor (f11dsc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("Converged in%13" NAG_IFMT " iterations\n", itn);
printf("Final residual norm = %11.3e\n\n", rnorm);
/* Output x */
printf("%14s\n", "Solution");
for (i = 0; i < n; i++)
printf("(%13.4e, %13.4e)\n", x[i].re, x[i].im);

END:
NAG_FREE(a);
NAG_FREE(b);
NAG_FREE(x);
NAG_FREE(icol);
NAG_FREE(irow);
return exit_status;
}
```