## Permutation functions

Function: void gsl_permutation_reverse (gsl_permutation * p)
  This function reverses the elements of the permutation p.

Function: int gsl_permutation_inverse (gsl_permutation * inv, const gsl_permutation * p)
  This function computes the inverse of the permutation p, storing the result in inv.

Function: int gsl_permutation_next (gsl_permutation * p)
  This function advances the permutation p to the next permutation in lexicographic order and returns `GSL_SUCCESS`. If no further permutations are available it returns `GSL_FAILURE` and leaves p unmodified. Starting with the identity permutation and repeatedly applying this function will iterate through all possible permutations of a given order.

Function: int gsl_permutation_prev (gsl_permutation * p)
  This function steps backwards from the permutation p to the previous permutation in lexicographic order, returning `GSL_SUCCESS`. If no previous permutation is available it returns `GSL_FAILURE` and leaves p unmodified.