EXCALIBURAdaptive Constraint-Based Agents in Artificial Environments

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 [ Please note: The project has been discontinued as of May 31, 2005 and is superseded by the projects of the ii Labs. There won't be further updates to these pages. ]

## SRC-H2: Moving an Event

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.

### Selecting an Inconsistent Precondition Task

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.

### Selecting an Event to be Moved

For the inconsistency improvement of the chosen Precondition Task p, the events of the predecessor interval ip and the successor interval is of p's interval i are considered. The predecessor option is dropped if i or ip 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 sp is computed, which is the state that results from a state transition from the state of the predecessor interval of ip using the event of i, and a subsequent state transition from the resulting state using the event of ip. If one of the state transitions is not possible, the predecessor option is dropped.

For the successor option, a state ss is set to the state of is.

For each option, an improvement value Dp/Ds is computed as the state distance from the option's state sp/ss 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 Dp/Ds. If there are no options for the choice, the heuristic is stopped and a negative success value is returned.

### Moving the Event

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.

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