EXCALIBUR Adaptive Constraint-Based Agents in Artificial Environments |
[SYMBOLIC SRC] | [Structures] [Selection] [SRC-H1] [SRC-H2] [SRC-H3] [SRC-H4] [SRC-H5] |
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(Related publication: [PUBLink])
This heuristic is applicable if at least one State Task is connected to the SRC. The idea is to temporally move an event to a time point before a Precondition Task such that the Precondition Task becomes less inconsistent.
One of the SRC's inconsistent Precondition Tasks that is after the current time c is selected with a choice probability for a Precondition Task proportional to the inconsistency caused by the Precondition Task.
For the inconsistency improvement of the chosen Precondition Task p, the events of the predecessor interval i_{p} and the successor interval i_{s} of p's interval i are considered. The predecessor option is dropped if i or i_{p} are the first interval or if they begin before c. The successor option is dropped if i is the last interval.
For the predecessor option, a state s_{p} is computed, which is the state that results from a state transition from the state of the predecessor interval of i_{p} using the event of i, and a subsequent state transition from the resulting state using the event of i_{p}. If one of the state transitions is not possible, the predecessor option is dropped.
For the successor option, a state s_{s} is set to the state of i_{s}.
For each option, an improvement value D_{p}/D_{s} is computed as the state distance from the option's state s_{p}/s_{s} to the state of p, minus the state distance from i's state to that of p. If one of the computed improvement value is less or equal to zero, the corresponding option is dropped.
From all the options, an interval is chosen with a choice probability for an interval that is proportional to , where d is the improvement value D_{p}/D_{s}. If there are no options for the choice, the heuristic is stopped and a negative success value is returned.
The selection of a time point for the event placement is done in exactly the same way as SRC-H1's selection of a time point for the event insertion. All of the chosen interval's State Tasks are moved to the selected time point.
[SYMBOLIC SRC] | [Structures] [Selection] [SRC-H1] [SRC-H2] [SRC-H3] [SRC-H4] [SRC-H5] |
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Last update:
May 20, 2001 by Alexander Nareyek