```/* nag_real_cholesky_skyline (f01mcc) Example Program.
*
* Copyright 2017 Numerical Algorithms Group.
*
* Mark 26.1, 2017.
*/

#include <nag.h>
#include <stdio.h>
#include <nag_stdlib.h>
#include <nagf01.h>

int main(void)
{
Integer exit_status = 0, i, k, k1, k2, lal, n, *row = 0;
NagError fail;
double *a = 0, *al = 0, *d = 0;

INIT_FAIL(fail);

printf("nag_real_cholesky_skyline (f01mcc) Example Program Results\n");
/* Skip heading in data file */
scanf("%*[^\n]");
scanf("%" NAG_IFMT "", &n);
if (n >= 1) {
if (!(row = NAG_ALLOC(n, Integer)) || !(d = NAG_ALLOC(n, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
}
else {
printf("Invalid n.\n");
exit_status = 1;
return exit_status;
}
lal = 0;
for (i = 0; i < n; i++) {
scanf("%" NAG_IFMT "", &row[i]);
lal += row[i];
}
if (!(a = NAG_ALLOC(lal, double)) || !(al = NAG_ALLOC(lal, double)))
{
printf("Allocation failure\n");
exit_status = -1;
goto END;
}

k2 = 0;
for (i = 0; i < n; ++i) {
k1 = k2;
k2 = k2 + row[i];
for (k = k1; k < k2; k++)
scanf("%lf", &a[k]);
}
/* nag_real_cholesky_skyline (f01mcc).
* LDL^T factorization of real symmetric positive-definite
* variable-bandwidth (skyline) matrix
*/
nag_real_cholesky_skyline(n, a, lal, row, al, d, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_real_cholesky_skyline (f01mcc).\n%s\n",
fail.message);
exit_status = 1;
goto END;
}
printf("\n");
printf("   i    d[i]   Row i of unit lower triangle\n\n");
k2 = 0;
for (i = 0; i < n; ++i) {
k1 = k2;
k2 = k2 + row[i];
printf(" %3" NAG_IFMT "%8.3f", i, d[i]);
for (k = k1; k < k2; k++)
printf("%8.3f", al[k]);
printf("\n");
}
END:
NAG_FREE(row);
NAG_FREE(a);
NAG_FREE(al);
NAG_FREE(d);
return exit_status;
}
```