```/* nag_sum_sqs_update (g02btc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.2, 2017.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nag_string.h>
#include <nagf16.h>
#include <nagg02.h>
#include <nagx04.h>

int main(void)
{
/* Arrays */
char nag_enum_arg[40];
double *c = 0, *v = 0, *x = 0, *xbar = 0;
/* Scalars */
double alpha, sw, wt;
Integer exit_status, i, j, m, mm, n, nprint, incx;
Nag_SumSquare mean;
NagError fail;

INIT_FAIL(fail);

exit_status = 0;
printf("nag_sum_sqs_update (g02btc) Example Program Results\n");

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

incx = 1;
while (scanf("%39s %" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n]",
nag_enum_arg, &m, &n, &nprint) != EOF) {
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
mean = (Nag_SumSquare) nag_enum_name_to_value(nag_enum_arg);
/* Allocate memory */
if (!(c = NAG_ALLOC((m * m + m) / 2, double)) ||
!(v = NAG_ALLOC((m * m + m) / 2, double)) ||
!(x = NAG_ALLOC(m * incx, double)) || !(xbar = NAG_ALLOC(m, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

sw = 0.0;
for (i = 1; i <= n; ++i) {
scanf("%lf", &wt);
for (j = 1; j <= m; ++j)
scanf("%lf", &x[j - 1]);
scanf("%*[^\n] ");

/* Calculate the sums of squares and cross-products matrix */
/* nag_sum_sqs_update (g02btc).
* Update a weighted sum of squares matrix with a new
* observation
*/
nag_sum_sqs_update(mean, m, wt, x, incx, &sw, xbar, c, &fail);

if (fail.code != NE_NOERROR) {
printf("Error from nag_sum_sqs_update (g02btc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

if (i % nprint == 0 || i == n) {
printf("\n");
printf("---------------------------------------------\n");
printf("Observation: %4" NAG_IFMT "      Weight = %13.4f\n", i, wt);
printf("\n");
printf("---------------------------------------------\n");
printf("\n");

printf("Means\n");
for (j = 1; j <= m; ++j)
printf("%14.4f%s", xbar[j - 1], j % 4 == 0 || j == m ? "\n" : " ");
printf("\n");

/* Print the sums of squares and cross products matrix */
/* nag_pack_real_mat_print (x04ccc).
* Print real packed triangular matrix (easy-to-use)
*/
fflush(stdout);
nag_pack_real_mat_print(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_pack_real_mat_print (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_daxpby (f16ecc)
* Multiply real vector by scalar, preserving input vector
*/
nag_daxpby(mm, alpha, c, 1, 0.0, v, 1, &fail);

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

NAG_FREE(c);
NAG_FREE(v);
NAG_FREE(x);
NAG_FREE(xbar);
}

END:
NAG_FREE(c);
NAG_FREE(v);
NAG_FREE(x);
NAG_FREE(xbar);

return exit_status;
}
```