NAG Library Manual, Mark 29.3
```/* nag_correg_quantile_linreg_easy (g02qfc) Example Program.
*
* Copyright 2023 Numerical Algorithms Group.
*
* Mark 29.3, 2023.
*/
/* Pre-processor includes */
#include <nag.h>
#include <stdio.h>

#define B(I, J) b[(J)*m + I]
#define BU(I, J) bu[(J)*m + I]
#define BL(I, J) bl[(J)*m + I]
#define X(I, J) x[(I)*m + J]

int main(void) {
/* Integer scalar and array declarations */
Integer i, j, l, m, n, ntau;
Integer *info = 0;
Integer exit_status = 0;

/* NAG structures */
NagError fail;

/* Double scalar and array declarations */
double df;
double *b = 0, *bl = 0, *bu = 0, *tau = 0, *x = 0, *y = 0;

/* Initialize the error structure */
INIT_FAIL(fail);

printf(
"nag_correg_quantile_linreg_easy (g02qfc) Example Program Results\n\n");

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

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

/* Allocate memory for input arrays */
if (!(y = NAG_ALLOC(n, double)) || !(tau = NAG_ALLOC(ntau, double)) ||
!(x = NAG_ALLOC(n * m, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* Read in the data */
for (i = 0; i < n; i++) {
for (j = 0; j < m; j++)
scanf("%lf", &X(i, j));
scanf("%lf", &y[i]);
}
scanf("%*[^\n] ");

/* Read in the quantiles required */
for (l = 0; l < ntau; l++) {
scanf("%lf", &tau[l]);
}
scanf("%*[^\n] ");

/* Allocate memory for output arrays */
if (!(b = NAG_ALLOC(m * ntau, double)) ||
!(info = NAG_ALLOC(ntau, Integer)) ||
!(bl = NAG_ALLOC(m * ntau, double)) ||
!(bu = NAG_ALLOC(m * ntau, double))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

/* nag_correg_quantile_linreg_easy (g02qfc).Quantile linear regression, simple
interface, independent, identically distributed (IID) errors */
nag_correg_quantile_linreg_easy(n, m, x, y, ntau, tau, &df, b, bl, bu, info,
&fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_correg_quantile_linreg_easy (g02qfc).\n%s\n",
fail.message);
if (fail.code == NW_POTENTIAL_PROBLEM) {
for (i = 0; i < ntau; i++)
printf("%" NAG_IFMT " ", info[i]);
printf("\n");
} else {
exit_status = 1;
goto END;
}
}

/* Display the parameter estimates */
for (l = 0; l < ntau; l++) {
printf(" Quantile: %6.3f\n\n", tau[l]);
printf("         Lower   Parameter   Upper\n");
printf("         Limit   Estimate    Limit\n");
for (j = 0; j < m; j++) {
printf(" %3" NAG_IFMT "   %7.3f   %7.3f   %7.3f\n", j + 1, BL(j, l),
B(j, l), BU(j, l));
}
printf("\n\n");
}

END:

NAG_FREE(info);
NAG_FREE(b);
NAG_FREE(bl);
NAG_FREE(bu);
NAG_FREE(tau);
NAG_FREE(x);
NAG_FREE(y);

return (exit_status);
}
```