NAG Library Manual, Mark 28.4
```/* nag_sort_permute_invert (m01zac) Example Program.
*
* Copyright 2022 Numerical Algorithms Group.
*
* Mark 28.4, 2022.
*/

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

#ifdef __cplusplus
extern "C" {
#endif
static Integer NAG_CALL compare(const Nag_Pointer a, const Nag_Pointer b);
#ifdef __cplusplus
}
#endif

#define VEC(I, J) vec[(I)*tdvec + J]
int main(void) {
Integer exit_status = 0, tdvec;
NagError fail;
double *vec = 0;
size_t i, j, m, n, *rank = 0;

INIT_FAIL(fail);

/* Skip heading in data file */
scanf("%*[^\n]");
printf("nag_sort_permute_invert (m01zac) Example Program Results\n");
scanf("%" NAG_UFMT "%" NAG_UFMT "", &m, &n);
if (m >= 1 && n >= 1) {
if (!(vec = NAG_ALLOC(m * n, double)) || !(rank = NAG_ALLOC(m, size_t))) {
printf("Allocation failure\n");
exit_status = -1;
goto END;
}
tdvec = n;
} else {
printf("Invalid m or n.\n");
exit_status = 1;
return exit_status;
}
for (i = 0; i < m; ++i)
for (j = 0; j < n; ++j)
scanf("%lf", &VEC(i, j));
/* nag_sort_rank_sort (m01dsc).
* Rank sort of set of values of arbitrary data type
*/
nag_sort_rank_sort((Pointer)vec, m, (ptrdiff_t)(n * sizeof(double)), compare,
Nag_Ascending, rank, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sort_rank_sort (m01dsc).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
/* nag_sort_permute_invert (m01zac).
* Inverts a permutation converting a rank vector to an
* index vector or vice versa
*/
nag_sort_permute_invert(rank, m, &fail);
if (fail.code != NE_NOERROR) {
printf("Error from nag_sort_permute_invert (m01zac).\n%s\n", fail.message);
exit_status = 1;
goto END;
}
printf("Matrix with rows sorted according to column 1\n");
for (i = 0; i < m; ++i) {
for (j = 0; j < n; ++j)
printf(" %7.1f ", VEC(rank[i], j));
printf("\n");
}
END:
NAG_FREE(vec);
NAG_FREE(rank);
return exit_status;
}

static Integer NAG_CALL compare(const Nag_Pointer a, const Nag_Pointer b) {
double x = *((const double *)a);
double y = *((const double *)b);
return (x < y ? -1 : (x == y ? 0 : 1));
}
```