cs_randperm.c
Go to the documentation of this file.00001 #include "cs.h" 00002 /* return a random permutation vector, the identity perm, or p = n-1:-1:0. 00003 * seed = -1 means p = n-1:-1:0. seed = 0 means p = identity. otherwise 00004 * p = random permutation. */ 00005 int *cs_randperm (int n, int seed) 00006 { 00007 int *p, k, j, t ; 00008 if (seed == 0) return (NULL) ; /* return p = NULL (identity) */ 00009 p = cs_malloc (n, sizeof (int)) ; /* allocate result */ 00010 if (!p) return (NULL) ; /* out of memory */ 00011 for (k = 0 ; k < n ; k++) p [k] = n-k-1 ; 00012 if (seed == -1) return (p) ; /* return reverse permutation */ 00013 srand (seed) ; /* get new random number seed */ 00014 for (k = 0 ; k < n ; k++) 00015 { 00016 j = k + (rand ( ) % (n-k)) ; /* j = rand int in range k to n-1 */ 00017 t = p [j] ; /* swap p[k] and p[j] */ 00018 p [j] = p [k] ; 00019 p [k] = t ; 00020 } 00021 return (p) ; 00022 }