NAG Library Manual, Mark 28.4
```/* nag_sparse_real_symm_solve_jacssor (f11jec) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.4, 2022.
*
*/

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

int main(void) {
double *a = 0, *b = 0, *x = 0;
double omega;
double rnorm;
double tol;
Integer exit_status = 0;
Integer *icol, *irow;
Integer i, n, maxitn, itn, nnz;
char nag_enum_arg[40];
Nag_SparseSym_Method method;
Nag_SparseSym_PrecType precon;
Nag_Sparse_Comm comm;
NagError fail;

INIT_FAIL(fail);

printf(
"nag_sparse_real_symm_solve_jacssor (f11jec) Example Program Results\n");

/* Skip heading in data file  */
scanf(" %*[^\n]");

scanf("%" NAG_IFMT "%*[^\n]", &n);
scanf("%" NAG_IFMT "%*[^\n]", &nnz);
scanf("%39s", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
method = (Nag_SparseSym_Method)nag_enum_name_to_value(nag_enum_arg);
scanf("%39s%*[^\n]", nag_enum_arg);
precon = (Nag_SparseSym_PrecType)nag_enum_name_to_value(nag_enum_arg);
scanf("%lf%*[^\n]", &omega);
scanf("%lf%" NAG_IFMT "%*[^\n]", &tol, &maxitn);

/* Allocate memory */
x = NAG_ALLOC(n, double);
b = NAG_ALLOC(n, double);
a = NAG_ALLOC(nnz, double);
irow = NAG_ALLOC(nnz, Integer);
icol = NAG_ALLOC(nnz, Integer);
if (!irow || !icol || !a || !x || !b) {
printf("Allocation failure\n");
exit_status = 1;
goto END;
}

/* Read the matrix a */
for (i = 1; i <= nnz; ++i)
scanf("%lf%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &a[i - 1], &irow[i - 1],
&icol[i - 1]);

/* Read right-hand side vector b and initial approximate solution x */
for (i = 1; i <= n; ++i)
scanf("%lf", &b[i - 1]);
scanf(" %*[^\n]");

for (i = 1; i <= n; ++i)
scanf("%lf", &x[i - 1]);
scanf(" %*[^\n]");

/* Solve Ax = b  */
/* nag_sparse_real_symm_solve_jacssor (f11jec).
* Solver with Jacobi, SSOR, or no preconditioning
* (symmetric)
*/
nag_sparse_real_symm_solve_jacssor(method, precon, n, nnz, a, irow, icol,
omega, b, tol, maxitn, x, &rnorm, &itn,
&comm, &fail);

printf(" %s%10" NAG_IFMT "%s\n", "Converged in", itn, " iterations");
printf(" %s%16.3e\n", "Final residual norm =", rnorm);

/* Output x */
for (i = 1; i <= n; ++i)
printf(" %16.4e\n", x[i - 1]);

END:
NAG_FREE(irow);
NAG_FREE(icol);
NAG_FREE(a);
NAG_FREE(x);
NAG_FREE(b);

return exit_status;
}
```