NAG Library Manual, Mark 28.7
```/* nag_correg_ssqmat (g02buc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.7, 2022.
*/

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

int main(void) {
/* Arrays */
char nag_enum_mean, nag_enum_weight;
double *c = 0, *v = 0, *wmean = 0, *wt = 0, *x = 0;
double *wtptr = 0;
/* Scalars */
double alpha, sw;
Integer exit_status, j, k, m, mm, n, pdx;
Nag_SumSquare mean;
Nag_Boolean weight;
Nag_OrderType order;
NagError fail;

#ifdef NAG_COLUMN_MAJOR
#define X(I, J) x[(J - 1) * pdx + I - 1]
order = Nag_ColMajor;
#else
#define X(I, J) x[(I - 1) * pdx + J - 1]
order = Nag_RowMajor;
#endif

INIT_FAIL(fail);

exit_status = 0;
printf("nag_correg_ssqmat (g02buc) Example Program Results\n");

/* Skip heading in data file */
scanf("%*[^\n] ");
while (scanf("%39s %39s %" NAG_IFMT "%" NAG_IFMT "%*[^\n]", nag_enum_mean,
nag_enum_weight, &m, &n) != EOF) {
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
mean = (Nag_SumSquare)nag_enum_name_to_value(nag_enum_mean);
weight = (Nag_Boolean)nag_enum_name_to_value(nag_enum_weight);
/* Allocate memory */
if (!(c = NAG_ALLOC((m * m + m) / 2, double)) ||
!(v = NAG_ALLOC((m * m + m) / 2, double)) ||
!(wmean = NAG_ALLOC(m, double)) || !(wt = NAG_ALLOC(n, double)) ||
!(x = NAG_ALLOC(n * m, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

#ifdef NAG_COLUMN_MAJOR
pdx = n;
#else
pdx = m;
#endif

for (j = 1; j <= n; ++j)
scanf("%lf", &wt[j - 1]);
scanf("%*[^\n] ");
for (j = 1; j <= n; ++j) {
for (k = 1; k <= m; ++k)
scanf("%lf", &X(j, k));
}
scanf("%*[^\n] ");

if (weight)
wtptr = wt;

/* Calculate sums of squares and cross-products matrix */
/* nag_correg_ssqmat (g02buc).
* Computes a weighted sum of squares matrix
*/
nag_correg_ssqmat(order, mean, n, m, x, pdx, wtptr, &sw, wmean, c, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_correg_ssqmat (g02buc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

printf("\n");
printf("Means\n");
for (j = 1; j <= m; ++j)
printf("%14.4f%s", wmean[j - 1], j % 6 == 0 || j == m ? "\n" : " ");
if (wtptr) {
printf("\n");
printf("Weights\n");
for (j = 1; j <= n; ++j)
printf("%14.4f%s", wt[j - 1], j % 6 == 0 || j == n ? "\n" : " ");
printf("\n");
}

/* Print the sums of squares and cross products matrix */
/* nag_file_print_matrix_real_packed (x04ccc).
* Print real packed triangular matrix (easy-to-use)
*/
fflush(stdout);
nag_file_print_matrix_real_packed(
Nag_ColMajor, Nag_Upper, Nag_NonUnitDiag, m, c,
"Sums of squares and cross-products", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_packed (x04ccc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
if (sw > 1.0) {
/* Calculate the variance matrix */
alpha = 1.0 / (sw - 1.0);
mm = m * (m + 1) / 2;
/* v[] = alpha*c[] using
* nag_blast_daxpby (f16ecc)
* Multiply real vector by scalar, preserving input vector
*/
nag_blast_daxpby(mm, alpha, c, 1, 0.0, v, 1, &fail);

/* Print the variance matrix */
printf("\n");
/* nag_file_print_matrix_real_packed (x04ccc), see above. */
fflush(stdout);
nag_file_print_matrix_real_packed(Nag_ColMajor, Nag_Upper,
Nag_NonUnitDiag, m, v,
"Variance matrix", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_packed (x04ccc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
}

NAG_FREE(c);
NAG_FREE(v);
NAG_FREE(wmean);
NAG_FREE(wt);
NAG_FREE(x);
}

END:
NAG_FREE(c);
NAG_FREE(v);
NAG_FREE(wmean);
NAG_FREE(wt);
NAG_FREE(x);

return exit_status;
}
```