CS 470  Artificial Intelligence,  Winter 2021,  Instructor:  Jeffrey Horn ASSIGNMENTS

• Assignment 3  "INFORMED (Heuristic) SEARCH in Blocks World"
  • Handed out:   Tuesday, 3-2-21
    
  • Due:               Wednesday 3-10-21 (Tasks 1 and 2; Task 3 due date TBA)
    
  • Goals:
  1. Understand the effect of a heuristic on best-first search (i.e., that it can reduce the number of states visited in the state-space-search).
  2. Understand the effect of the informedness of the heuristic (i.e., that a more informed heuristic can significantly reduce the number of states visited in the search.)
  • CODE:   On Educat here
    
  • TASKS:
  • Task 1: 
    
  • Get statistics for our class spreadsheet. 
    
  1. Come up with your own problem (run it by me first; when approved it will show up here).   Make sure you know the length of the optimal plan.
  2. Solve your problem using the three different heuristics: h0, h4, and h6.   Record the number of states visited as reported by the solve function.
  3. Email me:  Your problem (as a pair of initial and goal states), the length of the OPTIMAL plan, the three measures (that is, number of states visited) of the heuristics h0, h4, and h6.
     
  • Task 2:
  • Design your own admissible heuristic that is better than our h6.  (To be admissable it must never overestimate the actual cost of a plan, which in our blocks world domain means the actual length (number of moves/operations).  To be better than h6 it must (1) never come up with a lower estimate than h6 and (2) at least SOMETIMES (meaning at least once!) come up with a BETTER estimate.   More rigorously, let's call your heuristic hx.   The for all states s1 and s2, h6(s1,s2) <e; hx(s1,s2) and for some pair of states sA and sB, h6(sA,sB) < hx(sA,sB).  We'll say then that your heuristic hx is more informed than h6.)
  • Deliverables: 
    
  1. Give me a clear description of your heuristic.
  2. Give me one example in which h6(sA,sB) < hx(sA,sB).   Be sure to show both the states and the heuristic values, for both h6 and your hx.  Also graph the states sA and sB (you can draw them by hand if you can do so clearly!).
     
  3. Argue (briefly) why for all states s1 and s2, h6(s1,s2) <= hx(s1,s2).
  • Task 3:
  • Implement your heuristic (hx).   Use it to solve your problem from Task 1.   Send me the number of states visited.