NAG Library Manual, Mark 29.3
```/* nag_correg_glm_gamma (g02gdc) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.3, 2023.
*
*/

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

#define X(I, J) x[(I)*tdx + J]
#define V(I, J) v[(I)*tdv + J]

int main(void) {
Integer exit_status = 0, i, ip, j, m, max_iter, n, print_iter, rank;
Integer *sx = 0;
Integer tdv, tdx;
double dev, df, eps, ex_power, scale, tol;
double *b = 0, *cov = 0, *offsetptr = (double *)0;
double *se = 0, *v = 0, *wt = 0, *wtptr, *x = 0, *y = 0;
char nag_enum_arg[40];
Nag_IncludeMean mean;
Nag_Boolean weight;
NagError fail;

INIT_FAIL(fail);

printf("nag_correg_glm_gamma (g02gdc) Example Program Results\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf(" %39s", nag_enum_arg);
/* nag_enum_name_to_value (x04nac).
* Converts NAG enum member name to value
*/
scanf(" %39s", nag_enum_arg);
mean = (Nag_IncludeMean)nag_enum_name_to_value(nag_enum_arg);
scanf(" %39s", nag_enum_arg);
weight = (Nag_Boolean)nag_enum_name_to_value(nag_enum_arg);
scanf("%" NAG_IFMT " %" NAG_IFMT " %" NAG_IFMT " %lf", &n, &m, &print_iter,
&scale);

if (n >= 2 && m >= 1) {
if (!(wt = NAG_ALLOC(n, double)) || !(x = NAG_ALLOC(n * (m), double)) ||
!(y = NAG_ALLOC(n, double)) || !(sx = NAG_ALLOC(m, Integer))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
tdx = m;
} else {
printf("Invalid n or m.\n");
exit_status = 1;
return exit_status;
}
if (weight) {
wtptr = wt;
for (i = 0; i < n; i++) {
for (j = 0; j < m; j++)
scanf("%lf", &X(i, j));
scanf("%lf%lf", &y[i], &wt[i]);
}
} else {
wtptr = (double *)0;
for (i = 0; i < n; i++) {
for (j = 0; j < m; j++)
scanf("%lf", &X(i, j));
scanf("%lf", &y[i]);
}
}
for (j = 0; j < m; j++)
scanf("%" NAG_IFMT "", &sx[j]);

/* Calculate ip */
ip = 0;
for (j = 0; j < m; j++)
if (sx[j] > 0)
ip += 1;
if (mean == Nag_MeanInclude)
ip += 1;
scanf("%lf", &ex_power);
else
ex_power = 0.0;

if (!(b = NAG_ALLOC(ip, double)) || !(v = NAG_ALLOC(n * (ip + 6), double)) ||
!(se = NAG_ALLOC(ip, double)) ||
!(cov = NAG_ALLOC(ip * (ip + 1) / 2, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
tdv = ip + 6;

/* Set other control parameters */
max_iter = 10;
tol = 5e-5;
eps = 1e-6;

/* nag_correg_glm_gamma (g02gdc).
* Fits a generalized linear model with gamma errors
*/
nag_correg_glm_gamma(link, mean, n, x, tdx, m, sx, ip, y, wtptr, offsetptr,
&scale, ex_power, &dev, &df, b, &rank, se, cov, v, tdv,
tol, max_iter, print_iter, "", eps, &fail);

if (fail.code == NE_NOERROR || fail.code == NE_LSQ_ITER_NOT_CONV ||
fail.code == NE_RANK_CHANGED || fail.code == NE_ZERO_DOF_ERROR) {
if (fail.code != NE_NOERROR) {
printf("Error from nag_correg_glm_gamma (g02gdc).\n%s\n", fail.message);
}
printf("\nDeviance = %13.4e\n", dev);
printf("Degrees of freedom = %3.1f\n\n", df);
printf("       Estimate     Standard error\n\n");
for (i = 0; i < ip; i++)
printf("%14.4f%14.4f\n", b[i], se[i]);
printf("\n");
printf("     y   fitted value  Residual  Leverage\n\n");
for (i = 0; i < n; ++i) {
printf("%7.1f%10.2f%12.4f%10.3f\n", y[i], V(i, 1), V(i, 4), V(i, 5));
}
} else {
printf("Error from nag_correg_glm_gamma (g02gdc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}

END:
NAG_FREE(wt);
NAG_FREE(x);
NAG_FREE(y);
NAG_FREE(sx);
NAG_FREE(b);
NAG_FREE(v);
NAG_FREE(se);
NAG_FREE(cov);

return exit_status;
}
```