author Peter Kovacs Thu, 15 Nov 2012 07:05:29 +0100 changeset 1178 21a9f829ab68 parent 1170 764826c6e2b4 child 1179 f6f6896a4724
Optional iteration limit in HowardMmc (#438)
 lemon/howard_mmc.h file | annotate | diff | comparison | revisions test/min_mean_cycle_test.cc file | annotate | diff | comparison | revisions
     1.1 --- a/lemon/howard_mmc.h	Thu Nov 08 09:07:41 2012 +0100
1.2 +++ b/lemon/howard_mmc.h	Thu Nov 15 07:05:29 2012 +0100
1.3 @@ -149,6 +149,23 @@
1.4      /// The \ref HowardMmcDefaultTraits "traits class" of the algorithm
1.5      typedef TR Traits;
1.6
1.7 +    /// \brief Constants for the causes of search termination.
1.8 +    ///
1.9 +    /// Enum type containing constants for the different causes of search
1.10 +    /// termination. The \ref findCycleMean() function returns one of
1.11 +    /// these values.
1.12 +    enum TerminationCause {
1.13 +
1.14 +      /// No directed cycle can be found in the digraph.
1.15 +      NO_CYCLE = 0,
1.16 +
1.17 +      /// Optimal solution (minimum cycle mean) is found.
1.18 +      OPTIMAL = 1,
1.19 +
1.20 +      /// The iteration count limit is reached.
1.21 +      ITERATION_LIMIT
1.22 +    };
1.23 +
1.24    private:
1.25
1.26      TEMPLATE_DIGRAPH_TYPEDEFS(Digraph);
1.27 @@ -324,25 +341,46 @@
1.28        return findCycleMean() && findCycle();
1.29      }
1.30
1.31 -    /// \brief Find the minimum cycle mean.
1.32 +    /// \brief Find the minimum cycle mean (or an upper bound).
1.33      ///
1.34      /// This function finds the minimum mean cost of the directed
1.35 -    /// cycles in the digraph.
1.36 +    /// cycles in the digraph (or an upper bound for it).
1.37      ///
1.38 -    /// \return \c true if a directed cycle exists in the digraph.
1.39 -    bool findCycleMean() {
1.40 +    /// By default, the function finds the exact minimum cycle mean,
1.41 +    /// but an optional limit can also be specified for the number of
1.42 +    /// iterations performed during the search process.
1.43 +    /// The return value indicates if the optimal solution is found
1.44 +    /// or the iteration limit is reached. In the latter case, an
1.45 +    /// approximate solution is provided, which corresponds to a directed
1.46 +    /// cycle whose mean cost is relatively small, but not necessarily
1.47 +    /// minimal.
1.48 +    ///
1.49 +    /// \param limit  The maximum allowed number of iterations during
1.50 +    /// the search process. Its default value implies that the algorithm
1.51 +    /// runs until it finds the exact optimal solution.
1.52 +    ///
1.53 +    /// \return The termination cause of the search process.
1.55 +    TerminationCause findCycleMean(int limit = std::numeric_limits<int>::max()) {
1.56        // Initialize and find strongly connected components
1.57        init();
1.58        findComponents();
1.59
1.60        // Find the minimum cycle mean in the components
1.61 +      int iter_count = 0;
1.62 +      bool iter_limit_reached = false;
1.63        for (int comp = 0; comp < _comp_num; ++comp) {
1.64          // Find the minimum mean cycle in the current component
1.65          if (!buildPolicyGraph(comp)) continue;
1.66          while (true) {
1.67 +          if (++iter_count > limit) {
1.68 +            iter_limit_reached = true;
1.69 +            break;
1.70 +          }
1.71            findPolicyCycle();
1.72            if (!computeNodeDistances()) break;
1.73          }
1.74 +
1.75          // Update the best cycle (global minimum mean cycle)
1.76          if ( _curr_found && (!_best_found ||
1.77               _curr_cost * _best_size < _best_cost * _curr_size) ) {
1.78 @@ -351,8 +389,15 @@
1.79            _best_size = _curr_size;
1.80            _best_node = _curr_node;
1.81          }
1.82 +
1.83 +        if (iter_limit_reached) break;
1.84        }
1.85 -      return _best_found;
1.86 +
1.87 +      if (iter_limit_reached) {
1.88 +        return ITERATION_LIMIT;
1.89 +      } else {
1.90 +        return _best_found ? OPTIMAL : NO_CYCLE;
1.91 +      }
1.92      }
1.93
1.94      /// \brief Find a minimum mean directed cycle.

     2.1 --- a/test/min_mean_cycle_test.cc	Thu Nov 08 09:07:41 2012 +0100
2.2 +++ b/test/min_mean_cycle_test.cc	Thu Nov 15 07:05:29 2012 +0100
2.3 @@ -110,7 +110,7 @@
2.4                   const SmartDigraph::ArcMap<int>& cm,
2.5                   int cost, int size) {
2.6    MMC alg(gr, lm);
2.7 -  alg.findCycleMean();
2.8 +  check(alg.findCycleMean(), "Wrong result");
2.9    check(alg.cycleMean() == static_cast<double>(cost) / size,
2.10          "Wrong cycle mean");
2.11    alg.findCycle();
2.12 @@ -210,6 +210,13 @@
2.13      checkMmcAlg<HowardMmc<GR, IntArcMap> >(gr, l2, c2,  5, 2);
2.14      checkMmcAlg<HowardMmc<GR, IntArcMap> >(gr, l3, c3,  0, 1);
2.15      checkMmcAlg<HowardMmc<GR, IntArcMap> >(gr, l4, c4, -1, 1);
2.16 +
2.17 +    // Howard with iteration limit
2.18 +    HowardMmc<GR, IntArcMap> mmc(gr, l1);
2.19 +    check((mmc.findCycleMean(2) == HowardMmc<GR, IntArcMap>::ITERATION_LIMIT),
2.20 +      "Wrong termination cause");
2.21 +    check((mmc.findCycleMean(4) == HowardMmc<GR, IntArcMap>::OPTIMAL),
2.22 +      "Wrong termination cause");
2.23    }
2.24
2.25    return 0;