Zoltan2 Version of the Day
Zoltan2_AlgRandom.hpp
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00005 //   Zoltan2: A package of combinatorial algorithms for scientific computing
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00045 #ifndef _ZOLTAN2_ALGRANDOM_HPP_
00046 #define _ZOLTAN2_ALGRANDOM_HPP_
00047 
00048 #include <Zoltan2_IdentifierModel.hpp>
00049 #include <Zoltan2_OrderingSolution.hpp>
00050 
00051 
00056 
00057 
00058 namespace Zoltan2{
00059 
00060 template <typename Adapter>
00061 int AlgRandom(
00062   const RCP<IdentifierModel<Adapter> > &model, 
00063   const RCP<OrderingSolution<typename Adapter::gid_t,
00064                              typename Adapter::lno_t> > &solution,
00065   const RCP<Teuchos::ParameterList> &pl,
00066   const RCP<Teuchos::Comm<int> > &comm
00067 ) 
00068 {
00069   typedef typename Adapter::lno_t lno_t;
00070   typedef typename Adapter::gno_t gno_t;
00071   typedef typename Adapter::gid_t gid_t;
00072   typedef typename Adapter::scalar_t scalar_t;
00073 
00074   int ierr= 0;
00075 
00076   HELLO;
00077 
00078   // This is the classic Knuth shuffle, also known as Fisher-Yates shuffle.
00079   // References:
00080   //   D.E. Knuth, "The Art of Computer Programming", volume 2, 1969.
00081   //   R. Durstenfeld, "Algorithm 235: Random permutation", CACM, vol. 7, 1964.
00082 
00083   // Start with the identity permutation.
00084   const size_t n = model->getLocalNumIdentifiers();
00085   lno_t *perm;
00086   perm = (lno_t *) (solution->getPermutationRCP().getRawPtr());
00087   if (perm){
00088     for (size_t i=0; i<n; i++){
00089       perm[i] = i;
00090     }
00091   }
00092   else
00093     // throw exception?
00094     ierr = -1;
00095 
00096   // Swap random pairs of indices in perm.
00097   lno_t j, temp;
00098   for (lno_t i=n-1; i>0; i--){
00099     // Choose j randomly in [0,i]
00100     j = rand() % (i+1);
00101     // Swap (perm[i], perm[j])
00102     temp = perm[i];
00103     perm[i] = perm[j];
00104     perm[j] = temp;
00105   }
00106 
00107   return ierr;
00108 
00109 }
00110 
00111 }
00112 #endif