examples/example_permute.cpp

   1 /*  This file is part of libDAI - http://www.libdai.org/
   2  *
   3  *  libDAI is licensed under the terms of the GNU General Public License version
   4  *  2, or (at your option) any later version. libDAI is distributed without any
   5  *  warranty. See the file COPYING for more details.
   6  *
   7  *  Copyright (C) 2008-2009  Joris Mooij  [joris dot mooij at libdai dot org]
   8  */
   9
  10
  11 #include <dai/varset.h>
  12 #include <dai/index.h>
  13 #include <iostream>
  14 #include <iomanip>
  15
  16 using namespace std;
  17 using namespace dai;
  18
  19 int main() {
  20     Var x0(0, 2);   // Define binary  variable x0 (with label 0)
  21     Var x1(1, 3);   // Define ternary variable x1 (with label 1)
  22     Var x2(2, 2);   // Define binary  variable x2 (with label 2)
  23
  24     // Define vector V = (x1, x2, x0)
  25     vector<Var> V;      // Define a vector of variables
  26     V.push_back( x1 );  // V[0] = x1;
  27     V.push_back( x2 );  // V[1] = x2;
  28     V.push_back( x0 );  // V[2] = x0;
  29     cout << "V = " << V << endl; // Note that the elements of X are not necessarily ordered according to their labels
  30
  31     // Define set X = {x0, x1, x2}
  32     VarSet X; // empty
  33     X |= x2;  // X = {x2}
  34     X |= x0;  // X = {x0, x2}
  35     X |= x1;  // X = {x0, x1, x2}
  36     cout << "X = " << X << endl; // Note that the elements of X are ordered according to their labels
  37
  38     cout << "Note that the ordering of the variables in X is the canonical ordering" << endl;
  39     cout << "(ascendingly according to their labels) but the ordering in V is different." << endl << endl;
  40
  41     // N = number of variables in V (and X)
  42     size_t N = V.size();
  43
  44     // Define a Permute object based on the variables in V
  45     Permute sigma(V);
  46     // Each Var in V corresponds with a dimension in a multi-dimensional array.
  47     // The permutation sigma permutes these dimensions from the canonical ordering
  48     // (sorted ascendingly on the label of the variable, i.e., the same ordering as
  49     // in X) into the ordering these variables have in V.
  50     cout << "The permutation between both variable orderings is sigma = " << sigma.sigma() << ", or more verbosely:" << endl;
  51     for( size_t n = 0; n < N; n++ )
  52         cout << "  sigma[" << n << "] = " << sigma[n] << endl;
  53     cout << "This means that variable V[sigma[n]] should correspond with the n'th variable in X (for n=0,...," << (N-1) << ")...";
  54     // Check whether the permutation works as advertised
  55     VarSet::const_iterator X_n = X.begin();
  56     for( size_t n = 0; n < N; n++, X_n++ )
  57         DAI_ASSERT( V[sigma[n]] == *X_n );
  58     cout << "OK. " << endl << endl;
  59
  60     // Iterate over the joint states of the variables, according to the ordering in V
  61     cout << "The states of the variables x0,x1,x2 are, according to the ordering in V:" << endl;
  62     cout << "SV:  x0:  x1:  x2:" << endl;
  63     std::vector<size_t> ranges;
  64     for( size_t i = 0; i < V.size(); i++ )
  65         ranges.push_back( V[i].states() );
  66     for( multifor SV(ranges); SV.valid(); ++SV )
  67         cout << setw(2) << (size_t)SV << "    " << SV[sigma[0]] << "    " << SV[sigma[1]] << "    " << SV[sigma[2]] << endl;
  68     cout << endl;
  69
  70     // Iterate over the joint states of the variables, according to the canonical ordering in X
  71     cout << "The states of the variables x0,x1,x2 are, according to the canonical ordering in X:" << endl;
  72     cout << "SX:  x0:  x1:  x2:" << endl;
  73     for( State SX(X); SX.valid(); SX++ )
  74         cout << setw(2) << SX << "    " << SX(x0) << "    " << SX(x1) << "    " << SX(x2) << endl;
  75     cout << endl;
  76
  77     // The main functionality of the Permute object is to calculate the induced permutation of linear indices of joint states
  78     cout << "The permutation sigma induces the following permutation of linear indices of joint states:" << endl;
  79     cout << "SV:  SX:" << endl;
  80     for( size_t li = 0; li < X.nrStates(); li++ )
  81         cout << setw(2) << li << "   " << setw(2) << sigma.convertLinearIndex( li ) << endl;
  82
  83     return 0;
  84 }