NAG Library Manual, Mark 29
```/* nag_mv_cluster_kmeans (g03efc) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.0, 2023.
*
*/

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

#define CMEANS(I, J) cmeans[(I)*tdcmeans + J]
#define X(I, J) x[(I)*tdx + J]
int main(void) {
Integer exit_status = 0, i, *inc = 0, *isx = 0, j, k, m, maxit, n, *nic = 0,
nvar;
Integer tdcmeans, tdx;
NagError fail;
char weight[2];
double *cmeans = 0, *css = 0, *csw = 0, *wt = 0, *wtptr, *x = 0;

INIT_FAIL(fail);

printf("nag_mv_cluster_kmeans (g03efc) Example Program Results"
"\n\n");

/* Skip heading in the data file */
scanf("%*[^\n]");
scanf("%1s", weight);
scanf("%" NAG_IFMT "", &n);
scanf("%" NAG_IFMT "", &m);
scanf("%" NAG_IFMT "", &nvar);
scanf("%" NAG_IFMT "", &k);
scanf("%" NAG_IFMT "", &maxit);

if (n >= 2 && nvar >= 1 && m >= nvar && k >= 2) {
if (!(cmeans = NAG_ALLOC((k) * (nvar), double)) ||
!(css = NAG_ALLOC(k, double)) || !(csw = NAG_ALLOC(k, double)) ||
!(wt = NAG_ALLOC(n, double)) || !(x = NAG_ALLOC((n) * (m), double)) ||
!(inc = NAG_ALLOC(n, Integer)) || !(isx = NAG_ALLOC(m, Integer)) ||
!(nic = NAG_ALLOC(k, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
tdx = m;
tdcmeans = nvar;
} else {
printf("Invalid n or nvar or m or k.\n");
exit_status = 1;
return exit_status;
}
if (*weight == 'W') {
for (i = 0; i < n; ++i) {
for (j = 0; j < m; ++j)
scanf("%lf", &X(i, j));
scanf("%lf", &wt[i]);
}
wtptr = wt;
} else {
for (i = 0; i < n; ++i) {
for (j = 0; j < m; ++j)
scanf("%lf", &X(i, j));
}
wtptr = 0;
}
for (i = 0; i < k; ++i) {
for (j = 0; j < nvar; ++j)
scanf("%lf", &CMEANS(i, j));
}
for (j = 0; j < m; ++j)
scanf("%" NAG_IFMT "", &isx[j]);

/* nag_mv_cluster_kmeans (g03efc).
* K-means
*/
nag_mv_cluster_kmeans(n, m, x, tdx, isx, nvar, k, cmeans, tdcmeans, wtptr,
inc, nic, css, csw, maxit, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_mv_cluster_kmeans (g03efc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

printf("\nThe cluster each point belongs to\n");
for (i = 0; i < n; ++i)
printf(" %6" NAG_IFMT "%s", inc[i], (i + 1) % 10 ? "" : "\n");

printf("\n\nThe number of points in each cluster\n");
for (i = 0; i < k; ++i)
printf(" %6" NAG_IFMT "", nic[i]);

printf("\n\nThe within-cluster sum of weights of each cluster\n");
for (i = 0; i < k; ++i)
printf(" %9.2f", csw[i]);

printf("\n\nThe within-cluster sum of squares of each cluster\n\n");
for (i = 0; i < k; ++i)
printf(" %13.4f", css[i]);

printf("\n\nThe final cluster centres\n");
printf("                  1       2       3       4       5\n");
for (i = 0; i < k; ++i) {
printf(" %5" NAG_IFMT "     ", i + 1);
for (j = 0; j < nvar; ++j)
printf("%8.4f", CMEANS(i, j));
printf("\n");
}
END:
NAG_FREE(cmeans);
NAG_FREE(css);
NAG_FREE(csw);
NAG_FREE(wt);
NAG_FREE(x);
NAG_FREE(inc);
NAG_FREE(isx);
NAG_FREE(nic);
return exit_status;
}
```