means / ends analysis

Pieces

• means /ends
• planning
• selected trial & error

1. Form a queue with current state
2. Until queue is empty or goal reached

• if no untried procedure for reducing differences between current & goal
• then remove first goal from queue
• else if procedure precondition not satisfied then use GPS with precondition as sub-goal
• else use procedure to make new state q+ head of queue

1. If goal state found turn announce success else announce failure

Domain areas that can cause GPS problems

1. Clobbered sibling problem -- this focuses on short term, and is not looking at the big picture
2. Leap before you look problem -- this is when you jump off the cliff before you decide if you can land safe
3. Recursive sub-goal problem -- VCR setup tape to set up your VCR
4. Lack of intermediate feedback -- announce failure without thinking
5. Adding look ahead - not looking after you leap
6. lack of descriptive power
7. Perfect information required
8. Interacting problem goals (co-routines)

SOAR - derived from GPS

• attempts to model human cognition
• version of MYCIN
• Power robot to move through cluttered rooms

SOAR - Automatic Preference Analyzer

• Collect all states that are labeled acceptable
• Discard all acceptable states that are also labeled rejected
• Determine the domminance relations as follows:
• State A dominates state B if there is a better link from A to B but no better link from B to A
• State A dominates state B if there is a worse link from B to A but no worse link from A to B
• A state labeled best, and not dominated by any other state, dominates all other states
• A state labeled worst, which does not dominate any other state, is dominated by all other states
• Discard all dominated states
• Select the next state from among those remaining as follows:
• If only one other state remains, select it.
• Otherwise, if no states remain, select the current state, unless it is marked rejected
• Otherwise, if all states are connected by indifferent links,
• If the current state is one of the remainig states, keep it.
• Otherwise, select a state at random
• Othewise, announce an impasse