```/* nag_fit_dim1_cheb_deriv (e02ahc) Example Program.
*
* Copyright 2020 Numerical Algorithms Group.
*
* Mark 27.1, 2020.
*/

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

int main(void) {
/* Initialized data */
const double xmin = -0.5;
const double xmax = 2.5;
const double a[7] = {2.53213, 1.13032, 0.2715, 0.04434,
0.00547, 5.4e-4,  4e-5};

/* Scalars */
double deriv, deriv2, patm1, x;
Integer exit_status, i, m, n, one;
NagError fail;

/* Arrays */

INIT_FAIL(fail);

exit_status = 0;
printf("nag_fit_dim1_cheb_deriv (e02ahc) Example Program Results\n");

n = 6;
one = 1;

/* Allocate memory */
if (!(adif = NAG_ALLOC(n + 1, double)) ||
!(adif2 = NAG_ALLOC(n + 1, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* nag_fit_dim1_cheb_deriv (e02ahc).
* Derivative of fitted polynomial in Chebyshev series form
*/
nag_fit_dim1_cheb_deriv(n, xmin, xmax, a, one, &patm1, adif, one, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fit_dim1_cheb_deriv (e02ahc) call 1.\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

/* nag_fit_dim1_cheb_deriv (e02ahc), see above. */
if (fail.code != NE_NOERROR) {
printf("Error from nag_fit_dim1_cheb_deriv (e02ahc) call 2.\n%s\n",
fail.message);
exit_status = 1;
goto END;
}

m = 4;
printf("\n");
printf("   i  Argument    1st deriv    2nd deriv\n");

for (i = 1; i <= m; ++i) {
x = (xmin * (double)(m - i) + xmax * (double)(i - 1)) / (double)(m - 1);
/* nag_fit_dim1_cheb_eval2 (e02akc).
* Evaluation of fitted polynomial in one variable from
* Chebyshev series form
*/
nag_fit_dim1_cheb_eval2(n, xmin, xmax, adif, one, x, &deriv, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fit_dim1_cheb_eval2 (e02akc) call 1.\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
/* nag_fit_dim1_cheb_eval2 (e02akc), see above. */
nag_fit_dim1_cheb_eval2(n, xmin, xmax, adif2, one, x, &deriv2, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_fit_dim1_cheb_eval2 (e02akc) call 2.\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("%4" NAG_IFMT "%9.4f    %9.4f    %9.4f    \n", i, x, deriv, deriv2);
}

END: