```/* nag_sparse_nherm_precon_bdilu (f11dtc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.2, 2017.
*/

#include <nag.h>
#include <nagf11.h>
#include <nag_stdlib.h>

static void overlap(Integer *n, Integer *nnz, Integer *irow, Integer *icol,
Integer *nb, Integer *istb, Integer *indb, Integer *lindb,
Integer *nover, Integer *iwork);

int main(void)
{

/* Scalars */
double dtolg;
Integer i, j, k, la, lfillg, lindb, liwork, minval, mb, n, nb, nnz, nnzc,
nover;
Integer exit_status = 0, maxval_ret = 9999;
Nag_SparseNsym_Piv pstrag;
Nag_SparseNsym_Fact milug;

/* Arrays */
char nag_enum_arg[40];
double *dtol = 0;
Complex *a = 0;
Integer *icol = 0, *idiag = 0, *indb = 0, *ipivp = 0, *ipivq = 0, *irow = 0;
Integer *istb = 0, *istr = 0, *iwork = 0, *lfill = 0, *npivm = 0;
Nag_SparseNsym_Piv *pstrat;
Nag_SparseNsym_Fact *milu;

/* Nag Types */
NagError fail;

printf("nag_sparse_nherm_precon_bdilu (f11dtc) Example Program Results\n\n");

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

/* Get the matrix order and number of nonzero entries. */
scanf("%" NAG_IFMT " %*[^\n]", &n);
scanf("%" NAG_IFMT " %*[^\n]", &nnz);

la = 20 * nnz;
lindb = 3 * n;
liwork = 9 * n + 3;

/* Allocate arrays */
a = NAG_ALLOC(la, Complex);
irow = NAG_ALLOC(la, Integer);
icol = NAG_ALLOC(la, Integer);

idiag = NAG_ALLOC(lindb, Integer);
indb = NAG_ALLOC(lindb, Integer);
ipivp = NAG_ALLOC(lindb, Integer);
ipivq = NAG_ALLOC(lindb, Integer);
istr = NAG_ALLOC(lindb + 1, Integer);

iwork = NAG_ALLOC(liwork, Integer);

if ((!a) || (!irow) || (!icol) || (!idiag) || (!indb) || (!ipivp) ||
(!ipivq) || (!istr) || (!iwork)) {
printf("Allocation failure!\n");
exit_status = -1;
goto END;
}

/* Initialize arrays */
for (i = 0; i < la; i++) {
a[i].re = 0.0;
a[i].im = 0.0;
irow[i] = 0;
icol[i] = 0;
}

for (i = 0; i < lindb; i++) {
indb[i] = 0;
ipivp[i] = 0;
ipivq[i] = 0;
istr[i] = 0;
idiag[i] = 0;
}
istr[lindb] = 0;

for (i = 0; i < liwork; i++) {
iwork[i] = 0;
}

/* Read the matrix A */
for (i = 0; i < nnz; i++) {
scanf(" ( %lf , %lf ) %" NAG_IFMT " %" NAG_IFMT "",
&a[i].re, &a[i].im, &irow[i], &icol[i]);
}
scanf("%*[^\n] ");

scanf("%" NAG_IFMT " %lf %*[^\n]", &lfillg, &dtolg);

/* nag_enum_name_to_value (x04nac): Converts NAG enum member name to value */
scanf("%39s %*[^\n]", nag_enum_arg);
pstrag = (Nag_SparseNsym_Piv) nag_enum_name_to_value(nag_enum_arg);

/* nag_enum_name_to_value (x04nac): Converts NAG enum member name to value */
scanf("%39s %*[^\n]", nag_enum_arg);
milug = (Nag_SparseNsym_Fact) nag_enum_name_to_value(nag_enum_arg);

scanf("%" NAG_IFMT " %" NAG_IFMT " %*[^\n]", &nb, &nover);

if (nb < 1)
{
printf("Value read for nb is out of range\n");
exit_status = -4;
goto END;
}

/* Allocate arrays */
dtol = NAG_ALLOC(nb, double);
istb = NAG_ALLOC(nb + 1, Integer);
lfill = NAG_ALLOC(nb, Integer);
npivm = NAG_ALLOC(nb, Integer);

pstrat = (Nag_SparseNsym_Piv *) NAG_ALLOC(nb, Nag_SparseNsym_Piv);
milu = (Nag_SparseNsym_Fact *) NAG_ALLOC(nb, Nag_SparseNsym_Fact);

if ((!dtol) || (!istb) || (!lfill) || (!npivm) || (!pstrat) || (!milu)) {
printf("Allocation failure!\n");
exit_status = -1;
goto END;
}

/* Initialize arrays */
for (i = 0; i < nb; i++) {
dtol[i] = 0.0;
istb[i] = 0;
lfill[i] = 0;
npivm[i] = 0;
}
istb[nb] = 0;

/* Define diagonal block indices.
* In this example use blocks of MB consecutive rows and initialize
* assuming no overlap.
*/
mb = (n + nb - 1) / nb;
for (k = 0; k < nb; k++) {
istb[k] = k * mb + 1;
}
istb[nb] = n + 1;

for (i = 0; i < n; i++) {
indb[i] = i + 1;
}

/* Modify INDB and ISTB to account for overlap. */
overlap(&n, &nnz, irow, icol, &nb, istb, indb, &lindb, &nover, iwork);

/* Output matrix and blocking details */
printf(" Original Matrix\n");
printf(" n     = %4" NAG_IFMT "\n", n);
printf(" nnz   = %4" NAG_IFMT "\n", nnz);
printf(" nb    = %4" NAG_IFMT "\n", nb);

for (k = 0; k < nb; k++) {
printf(" Block = %4" NAG_IFMT ",%12s = %4" NAG_IFMT ",", k + 1, "order",
istb[k + 1] - istb[k]);
minval = indb[istb[k] - 1];
for (j = istb[k]; j < istb[k + 1] - 1; j++) {
minval = MIN(minval, indb[j]);
}
printf("%13s = %4" NAG_IFMT "\n", "start row", minval);
}
printf("\n");

/* Set algorithmic parameters for each block from global values */
for (k = 0; k < nb; k++) {
lfill[k] = lfillg;
dtol[k] = dtolg;
pstrat[k] = pstrag;
milu[k] = milug;
}

/* Initialize fail */
INIT_FAIL(fail);

/* Calculate factorization
*
* nag_sparse_nherm_precon_bdilu (f11dtc). Calculates incomplete LU
* factorization of local or overlapping diagonal blocks, mostly used
* as incomplete LU preconditioner for complex sparse matrix.
*/

nag_sparse_nherm_precon_bdilu(n, nnz, a, la, irow, icol, nb, istb, indb,
lindb, lfill, dtol, pstrat, milu, ipivp,
ipivq, istr, idiag, &nnzc, npivm, &fail);

if (fail.code != NE_NOERROR) {
printf("Error from nag_sparse_nherm_precon_bdilu (f11dtc).\n%s\n\n",
fail.message);
exit_status = -2;
goto END;
}

/* Output details of the factorization */
printf(" Factorization\n");
printf(" nnzc  = %4" NAG_IFMT "\n\n", nnzc);
printf(" Elements of factorization\n");
printf("        i    j           c(i,  j)            Index\n");

for (k = 0; k < nb; k++) {
printf("  C_%1" NAG_IFMT
"  -------------------------------------------\n", k + 1);

/* Elements of the k-th block */
for (i = istr[istb[k] - 1] - 1; i < istr[istb[k + 1] - 1] - 1; i++) {
printf("%9" NAG_IFMT " %4" NAG_IFMT " %13.5e %13.5e %7" NAG_IFMT "\n",
irow[i], icol[i], a[i].re, a[i].im, i + 1);
}
}

k = 0;
maxval_ret = npivm[k];
for (k = 1; k < nb; k++) {
maxval_ret = MAX(maxval_ret, npivm[k]);
}

printf("\n Details of factorized blocks\n");
if (maxval_ret > 0) {

/* Including pivoting details. */
printf("  k   i    istr(i)   idiag(i)    indb(i)  ipivp(i)  ipivq(i)\n");
for (k = 0; k < nb; k++) {
i = istb[k] - 1;
printf("%3" NAG_IFMT " %3" NAG_IFMT " %10" NAG_IFMT " ", k + 1, i + 1,
istr[i]);
printf("%10" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT
"\n", idiag[i], indb[i], ipivp[i], ipivq[i]);

for (i = istb[k]; i < istb[k + 1] - 1; i++) {
printf("%3" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT " ",
i + 1, istr[i], idiag[i]);
printf("%10" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT "\n",
indb[i], ipivp[i], ipivq[i]);
}
printf(" -----------------------------------------------------\n");
}
}
else {

/* No pivoting on any block. */
printf("  k   i     istr(i)   idiag(i)    indb(i)\n");
for (k = 0; k < nb; k++) {
i = istb[k] - 1;
printf("%3" NAG_IFMT " %3" NAG_IFMT " %10" NAG_IFMT " ", k + 1, i + 1,
istr[i]);
printf("%10" NAG_IFMT " %10" NAG_IFMT "\n", idiag[i], indb[i]);

for (i = istb[k]; i < istb[k + 1] - 1; i++) {
printf("%7" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT " %10" NAG_IFMT
"\n", i + 1, istr[i], idiag[i], indb[i]);
}
printf("  --------------------------------------\n");
}
}

END:
NAG_FREE(a);
NAG_FREE(irow);
NAG_FREE(icol);
NAG_FREE(idiag);
NAG_FREE(indb);
NAG_FREE(ipivp);
NAG_FREE(ipivq);
NAG_FREE(istr);
NAG_FREE(dtol);
NAG_FREE(istb);
NAG_FREE(lfill);
NAG_FREE(npivm);
NAG_FREE(pstrat);
NAG_FREE(milu);
NAG_FREE(iwork);

return exit_status;
}

/* ************************************************************************** */

static void overlap(Integer *n, Integer *nnz, Integer *irow, Integer *icol,
Integer *nb, Integer *istb, Integer *indb, Integer *lindb,
Integer *nover, Integer *iwork)
{
/* Purpose
* =======
*
* This routine takes a set of row indices INDB defining the diagonal blocks
* to be used in nag_sparse_nherm_precon_bdilu (f11dtc) to define a block
* Jacobi or additive Schwarz preconditioner, and expands them to allow for
* NOVER levels of overlap.
*
* The pointer array ISTB is also updated accordingly, so that the returned
* values of ISTB and INDB can be passed on to
* nag_sparse_nherm_precon_bdilu (f11dtc) to define overlapping diagonal
* blocks.
*
* ----------------------------------------------------------------------- */

/* Scalars */
Integer i, ik, ind, iover, j, k, l, n21, nadd, row;

/* Find the number of nonzero elements in each row of the matrix A, and start
*/

for (i = 0; i < (*n); i++) {
iwork[i] = 0;
}

for (i = 0; i < (*nnz); i++) {
iwork[irow[i] - 1] = iwork[irow[i] - 1] + 1;
}
iwork[(*n)] = 1;

for (i = 0; i < (*n); i++) {
iwork[(*n) + i + 1] = iwork[(*n) + i] + iwork[i];
}

/* Loop over blocks. */
for (k = 0; k < (*nb); k++) {

/* Initialize marker array. */
for (j = 0; j < (*n); j++) {
iwork[j] = 0;
}

/* Mark the rows already in block K in the workspace array. */
for (l = istb[k]; l < istb[k + 1]; l++) {
iwork[indb[l - 1] - 1] = 1;
}

/* Loop over levels of overlap. */
for (iover = 1; iover <= (*nover); iover++) {

/* Initialize counter of new row indices to be added. */
ind = 0;

/* Loop over the rows currently in the diagonal block. */
for (l = istb[k]; l < istb[k + 1]; l++) {
row = indb[l - 1];

/* Loop over nonzero elements in row ROW. */
for (i = iwork[(*n) + row - 1]; i < iwork[(*n) + row]; i++) {

/* If the column index of the nonzero element is not in the
* existing set for this block, store it to be added later, and
* mark it in the marker array.
*/
if (iwork[icol[i - 1] - 1] == 0) {
iwork[icol[i - 1] - 1] = 1;
iwork[2 * (*n) + 1 + ind] = icol[i - 1];
ind = ind + 1;
}
}
}

/* Shift the indices in INDB and add the new entries for block K.
* Change ISTB accordingly.
*/
if (istb[(*nb)] + nadd - 1 > (*lindb)) {
printf("**** lindb too small, lindb = %" NAG_IFMT " ****\n", *lindb);
exit(-1);
}

for (i = istb[(*nb)] - 1; i >= istb[k + 1]; i--) {
indb[i + nadd - 1] = indb[i - 1];
}

n21 = 2 * (*n) + 1;
ik = istb[k + 1] - 1;

for (j = 0; j < nadd; j++) {
indb[ik + j] = iwork[n21 + j];
}

for (j = k + 1; j < (*nb) + 1; j++) {
}
}
}
return;
}
```