COIN-OR::LEMON - Graph Library

Changeset 1178:21a9f829ab68 in lemon


Ignore:
Timestamp:
11/15/12 07:05:29 (7 years ago)
Author:
Peter Kovacs <kpeter@…>
Branch:
default
Phase:
public
Message:

Optional iteration limit in HowardMmc? (#438)

Files:
2 edited

Legend:

Unmodified
Added
Removed
  • lemon/howard_mmc.h

    r1164 r1178  
    150150    typedef TR Traits;
    151151
     152    /// \brief Constants for the causes of search termination.
     153    ///
     154    /// Enum type containing constants for the different causes of search
     155    /// termination. The \ref findCycleMean() function returns one of
     156    /// these values.
     157    enum TerminationCause {
     158     
     159      /// No directed cycle can be found in the digraph.
     160      NO_CYCLE = 0,
     161   
     162      /// Optimal solution (minimum cycle mean) is found.
     163      OPTIMAL = 1,
     164
     165      /// The iteration count limit is reached.
     166      ITERATION_LIMIT
     167    };
     168
    152169  private:
    153170
     
    325342    }
    326343
    327     /// \brief Find the minimum cycle mean.
     344    /// \brief Find the minimum cycle mean (or an upper bound).
    328345    ///
    329346    /// This function finds the minimum mean cost of the directed
    330     /// cycles in the digraph.
    331     ///
    332     /// \return \c true if a directed cycle exists in the digraph.
    333     bool findCycleMean() {
     347    /// cycles in the digraph (or an upper bound for it).
     348    ///
     349    /// By default, the function finds the exact minimum cycle mean,
     350    /// but an optional limit can also be specified for the number of
     351    /// iterations performed during the search process.
     352    /// The return value indicates if the optimal solution is found
     353    /// or the iteration limit is reached. In the latter case, an
     354    /// approximate solution is provided, which corresponds to a directed
     355    /// cycle whose mean cost is relatively small, but not necessarily
     356    /// minimal.
     357    ///
     358    /// \param limit  The maximum allowed number of iterations during
     359    /// the search process. Its default value implies that the algorithm
     360    /// runs until it finds the exact optimal solution.
     361    ///
     362    /// \return The termination cause of the search process.
     363    /// For more information, see \ref TerminationCause.
     364    TerminationCause findCycleMean(int limit = std::numeric_limits<int>::max()) {
    334365      // Initialize and find strongly connected components
    335366      init();
     
    337368
    338369      // Find the minimum cycle mean in the components
     370      int iter_count = 0;
     371      bool iter_limit_reached = false;
    339372      for (int comp = 0; comp < _comp_num; ++comp) {
    340373        // Find the minimum mean cycle in the current component
    341374        if (!buildPolicyGraph(comp)) continue;
    342375        while (true) {
     376          if (++iter_count > limit) {
     377            iter_limit_reached = true;
     378            break;
     379          }
    343380          findPolicyCycle();
    344381          if (!computeNodeDistances()) break;
    345382        }
     383
    346384        // Update the best cycle (global minimum mean cycle)
    347385        if ( _curr_found && (!_best_found ||
     
    352390          _best_node = _curr_node;
    353391        }
    354       }
    355       return _best_found;
     392       
     393        if (iter_limit_reached) break;
     394      }
     395
     396      if (iter_limit_reached) {
     397        return ITERATION_LIMIT;
     398      } else {
     399        return _best_found ? OPTIMAL : NO_CYCLE;
     400      }
    356401    }
    357402
  • test/min_mean_cycle_test.cc

    r956 r1178  
    111111                 int cost, int size) {
    112112  MMC alg(gr, lm);
    113   alg.findCycleMean();
     113  check(alg.findCycleMean(), "Wrong result");
    114114  check(alg.cycleMean() == static_cast<double>(cost) / size,
    115115        "Wrong cycle mean");
     
    211211    checkMmcAlg<HowardMmc<GR, IntArcMap> >(gr, l3, c3,  0, 1);
    212212    checkMmcAlg<HowardMmc<GR, IntArcMap> >(gr, l4, c4, -1, 1);
     213   
     214    // Howard with iteration limit
     215    HowardMmc<GR, IntArcMap> mmc(gr, l1);
     216    check((mmc.findCycleMean(2) == HowardMmc<GR, IntArcMap>::ITERATION_LIMIT),
     217      "Wrong termination cause");
     218    check((mmc.findCycleMean(4) == HowardMmc<GR, IntArcMap>::OPTIMAL),
     219      "Wrong termination cause");
    213220  }
    214221
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