```/* nag_blast_dgbmv (f16pbc) Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
*
* Mark 27.1, 2020.
*/

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

int main(void) {

/* Scalars */
double alpha, beta;
Integer ab_size, exit_status, i, incx, incy, j, kl, ku;
Integer m, n, pdab, xlen, ylen;

/* Arrays */
double *ab = 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 AB(I, J) ab[(J - 1) * pdab + ku + I - J]
order = Nag_ColMajor;
#else
#define AB(I, J) ab[(I - 1) * pdab + kl + J - I]
order = Nag_RowMajor;
#endif

exit_status = 0;
INIT_FAIL(fail);

printf("nag_blast_dgbmv (f16pbc) Example Program Results\n\n");

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

/* Read the problem dimensions */
scanf("%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &m, &n,
&kl, &ku);
/* 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);
scanf("%lf %lf%*[^\n] ", &alpha, &beta);
scanf("%" NAG_IFMT "%" NAG_IFMT "%*[^\n] ", &incx, &incy);

pdab = kl + ku + 1;
#ifdef NAG_COLUMN_MAJOR
ab_size = pdab * n;
#else
ab_size = pdab * m;
#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 (!(ab = NAG_ALLOC(ab_size, 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 = MAX(1, i - kl); j <= MIN(n, i + ku); ++j)
scanf("%lf", &AB(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_blast_dgbmv (f16pbc).
* real valued band matrix-vector multiply.
*
*/
nag_blast_dgbmv(order, trans, m, n, kl, ku, alpha, ab, pdab, x, incx, beta, y,
incy, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_blast_dgbmv.\n%s\n", fail.message);
exit_status = 1;
goto END;
}

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

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

return exit_status;
}
```