NAG Library Manual, Mark 28.5
```/* nag_blast_dsyr2 (f16prc) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.5, 2022.
*/

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

int main(void) {

/* Scalars */
double alpha, beta;
Integer exit_status, i, incx, incy, j, n, pda, xlen, ylen;

/* Arrays */
double *a = 0, *x = 0, *y = 0;
char nag_enum_arg[40];

/* Nag Types */
NagError fail;
Nag_OrderType order;
Nag_UploType uplo;
Nag_MatrixType matrix;

#ifdef NAG_COLUMN_MAJOR
#define A(I, J) a[(J - 1) * pda + I - 1]
order = Nag_ColMajor;
#else
#define A(I, J) a[(I - 1) * pda + J - 1]
order = Nag_RowMajor;
#endif

exit_status = 0;
INIT_FAIL(fail);

printf("nag_blast_dsyr2 (f16prc) Example Program Results\n\n");

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

/* Read the problem dimension */
scanf("%" NAG_IFMT "%*[^\n] ", &n);

/* Read the uplo storage parameter */
scanf("%39s%*[^\n] ", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
uplo = (Nag_UploType)nag_enum_name_to_value(nag_enum_arg);

scanf("%lf%lf%*[^\n] ", &alpha, &beta);
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &incx, &incy);

pda = n;

xlen = MAX(1, 1 + (n - 1) * ABS(incx));
ylen = MAX(1, 1 + (n - 1) * ABS(incy));

if (n > 0) {
/* Allocate memory */
if (!(a = NAG_ALLOC(pda * n, double)) || !(x = NAG_ALLOC(xlen, double)) ||
!(y = NAG_ALLOC(ylen, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
} else {
printf("Invalid n\n");
exit_status = 1;
goto END;
}

/* Input matrix A and vector x */

if (uplo == Nag_Upper) {
for (i = 1; i <= n; ++i) {
for (j = i; j <= n; ++j)
scanf("%lf", &A(i, j));
scanf("%*[^\n] ");
}
} else {
for (i = 1; i <= n; ++i) {
for (j = 1; j <= i; ++j)
scanf("%lf", &A(i, j));
scanf("%*[^\n] ");
}
}
for (i = 0; i < xlen; ++i)
scanf("%lf%*[^\n] ", &x[i]);
for (i = 0; i < ylen; ++i)
scanf("%lf%*[^\n] ", &y[i]);

/* nag_blast_dsyr2 (f16prc).
* Rank two update of real symmetric matrix.
*
*/
nag_blast_dsyr2(order, uplo, n, alpha, x, incx, y, incy, beta, a, pda, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_blast_dsyr2 (f16prc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

if (uplo == Nag_Upper) {
matrix = Nag_UpperMatrix;
} else {
matrix = Nag_LowerMatrix;
}
/* Print updated matrix A */
/* nag_file_print_matrix_real_gen (x04cac).
* Print real general matrix (easy-to-use)
*/
fflush(stdout);
nag_file_print_matrix_real_gen(order, matrix, Nag_NonUnitDiag, n, n, a, pda,
"Updated Matrix A", 0, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_file_print_matrix_real_gen (x04cac).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(a);
NAG_FREE(x);
NAG_FREE(y);

return exit_status;
}
```