code: public static int[] cs_randperm(int n, int seed) {
          int p[], k, j, t;
          if (seed == 0)
              return (null); /* return p = NULL (identity) */
          p = new int[n]; /* allocate result */
          for (k = 0; k < n; k++)
              p[k] = n - k - 1;
          if (seed == -1)
              return (p); /* return reverse permutation */
          Random r = new Random(seed); /* get new random number seed */
          for (k = 0; k < n; k++) {
              j = k + r.nextInt(n - k); /* j = rand int in range k to n-1 */
              t = p[j]; /* swap p[k] and p[j] */
              p[j] = p[k];
              p[k] = t;
          }
          return (p);
      }
docs: Returns a random permutation vector, the identity perm, or p = n-1:-1:0.f
  seed = -1 means p = n-1:-1:0.f seed = 0 means p = identity. otherwise p =
  random permutation.
  
  @param n
  length of p
  @param seed
  0: natural, -1: reverse, random p oterwise
  @return p, null on error or for natural order