NAG Library Manual, Mark 29
```/* nag_sparse_complex_herm_precon_ilu_solve (f11jpc) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.0, 2023.
*/

#include <nag.h>

int main(void) {
/* Scalars */
Integer exit_status = 0;
double dscale, dtol;
Integer i, la, lfill, n, nnz, nnzc, npivm;
/* Arrays */
Complex *a = 0, *x = 0, *y = 0;
Integer *icol = 0, *ipiv = 0, *irow = 0, *istr = 0;
/* NAG types */
Nag_SparseSym_Fact mic;
Nag_SparseSym_Piv pstrat;
Nag_SparseSym_CheckData check;
NagError fail;

INIT_FAIL(fail);

printf(
"nag_sparse_complex_herm_precon_ilu_solve (f11jpc) Example Program Results");
printf("\n\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "%*[^\n]", &n);
scanf("%" NAG_IFMT "%*[^\n]", &nnz);

/* Allocate memory */
la = 3 * nnz;
if (!(a = NAG_ALLOC(la, Complex)) || !(x = NAG_ALLOC(n, Complex)) ||
!(y = NAG_ALLOC(n, Complex)) || !(icol = NAG_ALLOC(la, Integer)) ||
!(ipiv = NAG_ALLOC(n, Integer)) || !(irow = NAG_ALLOC(la, Integer)) ||
!(istr = NAG_ALLOC(n + 1, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
/* Read the matrix a */
for (i = 0; i <= nnz - 1; i++)
scanf(" ( %lf , %lf ) %" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &a[i].re,
&a[i].im, &irow[i], &icol[i]);
/* Read the vector y */
for (i = 0; i <= n - 1; i++)
scanf(" ( %lf , %lf ) ", &y[i].re, &y[i].im);

lfill = -1;
dtol = 0.0;
dscale = 0.0;
mic = Nag_SparseSym_UnModFact;
pstrat = Nag_SparseSym_MarkPiv;
/* Calculate Cholesky factorization using nag_sparse_complex_herm_precon_ichol
* (f11jnc).
*/
nag_sparse_complex_herm_precon_ichol(n, nnz, a, la, irow, icol, lfill, dtol,
mic, dscale, pstrat, ipiv, istr, &nnzc,
&npivm, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_complex_herm_precon_ichol (f11jnc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
/* Check the output value of npivm */
if (npivm != 0)
printf("Factorization is not complete \n");
else {
/* Solve complex linear system involving incomplete Cholesky factorization
*
*              H T
*       P L D L P x = y
*
* using nag_sparse_complex_herm_precon_ilu_solve (f11jpc).
*/
check = Nag_SparseSym_Check;
nag_sparse_complex_herm_precon_ilu_solve(n, a, la, irow, icol, ipiv, istr,
check, y, x, &fail);
if (fail.code != NE_NOERROR) {
printf(
"Error from nag_sparse_complex_herm_precon_ilu_solve (f11jpc).\n%s\n",
fail.message);
exit_status = 2;
goto END;
}
/* Output results */
printf("Solution of linear system \n");
for (i = 0; i <= n - 1; i++)
printf(" (%13.4e, %13.4e) \n", x[i].re, x[i].im);
}

END:
NAG_FREE(a);
NAG_FREE(x);
NAG_FREE(y);
NAG_FREE(icol);
NAG_FREE(ipiv);
NAG_FREE(irow);
NAG_FREE(istr);
return exit_status;
}
```