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Operator-counting constraints based on the delete relaxation. By default the constraints encode an easy-to-compute relaxation of h^+. If both use_time_vars and use_integer_vars are set to true and this is the only constriant in an operator-counting heursitic with integer variables for the operator counts, the resulting heuristic is the optimal delete-relaxation heuristic h^+. For details, see Operator-counting constraints based on the delete relaxation. By default the constraints encode an easy-to-compute relaxation of h^+^. If both use_time_vars and use_integer_vars are set to true and this is the only constraint in an operator-counting heuristic with integer variables for the operator counts, the resulting heuristic is the optimal delete-relaxation heuristic h^+^. For details, see
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 * ''use_integer_vars'' (bool): restrict auxiliary variables to integer values. These variables encode whether operators are used, facts are reached, which operator first achieves which fact, and in which order the operators are used. Restricting them to integers generally improves the heursitic value at the cost of increased runtime.  * ''use_integer_vars'' (bool): restrict auxiliary variables to integer values. These variables encode whether operators are used, facts are reached, which operator first achieves which fact, and in which order the operators are used. Restricting them to integers generally improves the heuristic value at the cost of increased runtime.
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Computes a set of landmarks in each state using the LM-cut method. For each landmark L the constraint sum_{o in L} Count_o >= 1 is added to the operator counting LP temporarily. After the heuristic value for the state is computed, all temporary constraints are removed again. For details, see Computes a set of landmarks in each state using the LM-cut method. For each landmark L the constraint sum_{o in L} Count_o >= 1 is added to the operator-counting LP temporarily. After the heuristic value for the state is computed, all temporary constraints are removed again. For details, see

Contents

  1. Delete relaxation constraints
  2. LM-cut landmark constraints
  3. Posthoc optimization constraints
  4. State equation constraints

Delete relaxation constraints

Operator-counting constraints based on the delete relaxation. By default the constraints encode an easy-to-compute relaxation of h+. If both use_time_vars and use_integer_vars are set to true and this is the only constraint in an operator-counting heuristic with integer variables for the operator counts, the resulting heuristic is the optimal delete-relaxation heuristic h+. For details, see 

delete_relaxation_constraints(use_time_vars=false, use_integer_vars=false)

  • use_time_vars (bool): use variables for time steps. With these additional variables the constraints enforce an order between the selected operators. Leaving this off (default) corresponds to the time relaxation by Imai and Fukunaga. Switching it on, can increase the heuristic value but will increase the size of the constraints which has a strong impact on runtime. Constraints involving time variables use a big-M encoding, so they are more useful if used with integer variables.

  • use_integer_vars (bool): restrict auxiliary variables to integer values. These variables encode whether operators are used, facts are reached, which operator first achieves which fact, and in which order the operators are used. Restricting them to integers generally improves the heuristic value at the cost of increased runtime.

LM-cut landmark constraints

Computes a set of landmarks in each state using the LM-cut method. For each landmark L the constraint sum_{o in L} Count_o >= 1 is added to the operator-counting LP temporarily. After the heuristic value for the state is computed, all temporary constraints are removed again. For details, see 

lmcut_constraints()

Posthoc optimization constraints

The generator will compute a PDB for each pattern and add the constraint h(s) <= sum_{o in relevant(h)} Count_o. For details, see 

pho_constraints(patterns=systematic(2))

State equation constraints

For each fact, a permanent constraint is added that considers the net change of the fact, i.e., the total number of times the fact is added minus the total number of times is removed. The bounds of each constraint depend on the current state and the goal state and are updated in each state. For details, see 

state_equation_constraints()

FastDownward: Doc/ConstraintGenerator (last edited 2024-10-07 12:37:27 by XmlRpcBot)