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cs_randperm.c 908 B
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    #include "cs.h"
    /* return a random permutation vector, the identity perm, or p = n-1:-1:0.
     * seed = -1 means p = n-1:-1:0.  seed = 0 means p = identity.  otherwise
     * p = random permutation.  */
    CS_INT *cs_randperm (CS_INT n, CS_INT seed)
    {
        CS_INT *p, k, j, t ;
        if (seed == 0) return (NULL) ;      /* return p = NULL (identity) */
        p = cs_malloc (n, sizeof (CS_INT)) ;   /* allocate result */
        if (!p) return (NULL) ;             /* out of memory */
        for (k = 0 ; k < n ; k++) p [k] = n-k-1 ;
        if (seed == -1) return (p) ;        /* return reverse permutation */
        srand (seed) ;                      /* get new random number seed */
        for (k = 0 ; k < n ; k++)
        {
            j = k + (rand ( ) % (n-k)) ;    /* j = rand integer in range k to n-1 */
            t = p [j] ;                     /* swap p[k] and p[j] */
            p [j] = p [k] ;
            p [k] = t ;
        }
        return (p) ;
    }