```/* nag_sparse_real_gen_precon_jacobi (f11dkc) Example Program.
*
* Copyright 2019 Numerical Algorithms Group.
*
* Mark 27.0, 2019.
*/
#include <nag.h>
int main(void)
{
/* Scalars */
Integer exit_status = 0;
double anorm, sigmax, stplhs, stprhs, tol;
Integer i, irevcm, iterm, itn, lwork, lwreq, m, maxitn, monit,
n, niter, nnz;
/* Arrays */
char nag_enum_arg[100];
double *a = 0, *b = 0, *diag = 0, *wgt = 0, *work = 0, *x = 0;
Integer *icol = 0, *irow = 0;
/* NAG types */
Nag_InitializeA init;
Nag_SparseNsym_Method method;
Nag_SparseNsym_PrecType precon;
Nag_NormType norm;
Nag_SparseNsym_Weight weight;
NagError fail, fail1;

INIT_FAIL(fail);
INIT_FAIL(fail1);

printf("nag_sparse_real_gen_precon_jacobi (f11dkc) Example Program Results \n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
scanf("%" NAG_IFMT "%*[^\n]", &nnz);
lwork = 200;
if (!(a = NAG_ALLOC((nnz), double)) ||
!(b = NAG_ALLOC((n), double)) ||
!(diag = NAG_ALLOC((n), double)) ||
!(wgt = NAG_ALLOC((n), double)) ||
!(work = NAG_ALLOC((lwork), double)) ||
!(x = NAG_ALLOC((n), double)) ||
!(icol = NAG_ALLOC((nnz), Integer)) ||
!(irow = NAG_ALLOC((nnz), Integer))
)
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Read or initialize the parameters for the iterative solver */
scanf("%99s%*[^\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("%99s%*[^\n]", nag_enum_arg);
precon = (Nag_SparseNsym_PrecType) nag_enum_name_to_value(nag_enum_arg);
scanf("%99s%*[^\n]", nag_enum_arg);
norm = (Nag_NormType) nag_enum_name_to_value(nag_enum_arg);
scanf("%99s%*[^\n]", nag_enum_arg);
weight = (Nag_SparseNsym_Weight) nag_enum_name_to_value(nag_enum_arg);
scanf("%" NAG_IFMT "%*[^\n]", &iterm);
scanf("%" NAG_IFMT "%lf%" NAG_IFMT "%*[^\n]", &m, &tol, &maxitn);
scanf("%" NAG_IFMT "%*[^\n]", &monit);

/* Read the parameters for the preconditioner */
scanf("%" NAG_IFMT "%*[^\n]", &niter);
anorm = 0.0;
sigmax = 0.0;

/* Read the nonzero elements of the matrix A */
for (i = 0; i <= nnz - 1; i++)
scanf("%lf%" NAG_IFMT "%" NAG_IFMT "%*[^\n]", &a[i], &irow[i], &icol[i]);

/* Read right-hand side vector b and initial approximate solution */
for (i = 0; i <= n - 1; i++)
scanf("%lf", &b[i]);
scanf("%*[^\n]");
for (i = 0; i <= n - 1; i++)
scanf("%lf", &x[i]);

/* nag_sparse_real_gen_basic_setup (f11bdc)
* Real sparse nonsymmetric linear systems, setup routine
*/
nag_sparse_real_gen_basic_setup(method, precon, norm, weight, iterm, n, m, tol,
maxitn, anorm, sigmax, monit, &lwreq, work,
lwork, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_real_gen_basic_setup (f11bdc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
/* call solver repeatedly to solve the equations
* Note that the arrays b and x are overwritten
* On final exit, x will contain the solution and b the residual vector
*/
irevcm = 0;
lwreq = lwork;
init = Nag_InitializeI;
while (irevcm != 4) {
/* nag_sparse_real_gen_basic_solver (f11bec)
* Real sparse nonsymmetric linear systems, solver routine
* preconditioned RGMRES, CGS, Bi-CGSTAB or TFQMR method
*/
nag_sparse_real_gen_basic_solver(&irevcm, x, b, wgt, work, lwreq, &fail);
switch (irevcm) {
case -1:
/* nag_sparse_real_gen_matvec (f11xac)
* Real sparse nonsymmetric matrix vector multiply
*/
nag_sparse_real_gen_matvec(Nag_Trans, n, nnz, a, irow, icol,
Nag_SparseNsym_NoCheck, x, b, &fail1);
break;
case 1:
nag_sparse_real_gen_matvec(Nag_NoTrans, n, nnz, a, irow, icol,
Nag_SparseNsym_NoCheck, x, b, &fail1);
break;
case 2:
/* nag_sparse_real_gen_precon_jacobi (f11dkc)
* Real sparse nonsymmetric linear systems, line Jacobi preconditioner
*/
nag_sparse_real_gen_precon_jacobi(Nag_SparseNsym_StoreCS, Nag_NoTrans, init,
niter, n, nnz, a, irow, icol,
Nag_SparseNsym_Check, x, b, diag, &fail1);
init = Nag_InputA;
break;
case 3:
/* nag_sparse_real_gen_basic_diag (f11bfc)
* Real sparse nonsymmetric linear systems, diagnostic for f11bec
*/
nag_sparse_real_gen_basic_diag(&itn, &stplhs, &stprhs, &anorm,
&sigmax, work, lwreq, &fail1);
printf("%" NAG_IFMT " %f \n", itn, stplhs);
}
if (fail1.code != NE_NOERROR)
irevcm = 6;
}
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_real_gen_basic_solver (f11bec)\n%s\n",
fail.message);
exit_status = 2;
goto END;
}

/* Obtain information about the computation */
nag_sparse_real_gen_basic_diag(&itn, &stplhs, &stprhs, &anorm, &sigmax,
work, lwreq, &fail);
/* Print the output data */
printf("\nFinal Results\n");
printf("Number of iterations for convergence:     %5" NAG_IFMT " \n", itn);
printf("Residual norm:                            %14.4e\n", stplhs);
printf("Right-hand side of termination criterion: %14.4e\n", stprhs);
printf("1-norm of matrix A:                       %14.4e\n\n", anorm);

/* Output x */
printf("%16s%16s\n", "Solution", "Residuals");
for (i = 0; i < n; i++)
printf("%16.4f%16.4e\n", x[i], b[i]);

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