```/* nag_dgemv (f16pac) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

#include <stdio.h>
#include <nag.h>
#include <nag_stdlib.h>
#include <nagf16.h>

int main(void)
{

/* Scalars */
double alpha, beta;
Integer exit_status, i, incx, incy, j, m, 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_TransType trans;

#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_dgemv (f16pac) Example Program Results\n\n");

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

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

/* Read the transpose parameter */
scanf("%39s%*[^\n] ", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
trans = (Nag_TransType) nag_enum_name_to_value(nag_enum_arg);
/* Read scalar parameters */
scanf("%lf%lf%*[^\n] ", &alpha, &beta);
/* Read increment parameters */
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &incx, &incy);

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

if (trans == Nag_NoTrans) {
xlen = MAX(1, 1 + (n - 1) * ABS(incx));
ylen = MAX(1, 1 + (m - 1) * ABS(incy));
}
else {
xlen = MAX(1, 1 + (m - 1) * ABS(incx));
ylen = MAX(1, 1 + (n - 1) * ABS(incy));
}

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

/* Input matrix A and vectors x and y */

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

/* nag_dgemv (f16pac).
* Matrix-vector multiply.
*
*/
nag_dgemv(order, trans, m, n, alpha, a, pda, x, incx, beta, y, incy, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_dgemv.\n%s\n", fail.message);
exit_status = 1;
goto END;
}

/* Print output vector y */
printf("%s\n", "  y");
for (i = 1; i <= ylen; ++i) {
printf("%11f\n", y[i - 1]);
}

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

return exit_status;
}
```