1. Supplemental slides for CSE 327 Prof. Jeff Heflin
Ch. 10 – Planning
Supplemental slides for CSE 327
Prof. Jeff Heflin

2. Goal-Based Agent Environment Agent sensors State
What the world is like now
How the world evolves
Environment
What it will be like if I do action A
What my actions do
What action I should do now
Goals
actuators
Agent
From Fig. 2.13, p. 52

3. Blocks World Example initial state goal actions
On(A,Table)  On(B,Table)  Clear(A)  Clear(B)  Clear(Table)  Block(A)  Block(B)
goal
On(A,B)
actions
Action(Move(b,x,y) , Precond: On(b,x)  Clear(b)  Clear(y)  Block(y), Effect: On(b,y)  Clear(x)  On(b,x)  Clear(y))
Action(MoveToTable(b,x), Precond: On(b,x)  Clear(b), Effect: On(b,Table)  Clear(x)  On(b,x))

4. Applicable Actions
an action a is applicable in any state that satisfies the precondition
e.g., Move(A,Table,B) is applicable in initial state
unify with action description
apply substitution  ={b/A, x/Table, y/B} to the action’s Precondition
initial state satisfies On(A,Table)  Clear(A)  Clear(B)  Block(B)
Action(Move(b,x,y),
Precond: On(b,x)  Clear(b)  Clear(y)  Block(y),
Effect: On(b,y)  Clear(x)  On(b,x)  Clear(y))
Action(MoveToTable(b,x),
Precond: On(b,x)  Clear(b),
Effect: On(b,Table)  Clear(x)  On(b,x))
Initial State:
On(A,Table)  On(B,Table)  Clear(A)  Clear(B)  Clear(Table)  Block(A)  Block(B)

5. A Blocks World Problem initial state goal state actions
On(A,Table)  On(B,Table)  On(C,Table)  Clear(A)  Clear(B)  Clear(C)  Clear(Table)  Block(A)  Block(B)  Block(C)
goal state
On(B,C)  On(A,B)  On(C,Table)
actions
Action(Move(b,x,y) , Precond: On(b,x)  Clear(b)  Clear(y)  Block(y), Effect: On(b,y)  Clear(x)  On(b,x)  Clear(y))
Action(MoveToTable(b,x), Precond: On(b,x)  Clear(b), Effect: On(b,Table)  Clear(x)  On(b,x))

6. Forward State-Space Search
Move(A,T,B)
MoveToTable(B,C)
Move(A,T,C)
Move(B,T,A)
Move(B,C,A)
On(A,T) ^ On(B,T) ^ On(C,T) ^ Clear(A) ^ Clear(B) ^ Clear(C) ^ Clear(T)
Move(B,T,C)
On(A,T) ^ On(B,T) ^ On(C,T) ^ Clear(A) ^ Clear(B) ^ Clear(C) ^ Clear(T) ^ On(B,C)
Move(A,T,B)
On(A,T) ^ On(C,T) ^ Clear(A) ^ Clear(B) ^ Clear(T) ^ On(B,C) ^ On(A,B)
Move(A,T,A)
Move(C,T,A)
spurious actions
Move(B,C,B)
Move(C,T,B)
MoveToTable(A,T)
MoveToTable(A,T)
MoveToTable(B,T)
MoveToTable(C,T)
spurious actions
Move(A,T,A)
Move(B,T,B)
Move(C,T,C)

7. Backward State-Space Search
On(B,C) ^ On(A,B) ^ On(C,T)
GOAL:
MoveToTable(C,x)
Move(B,x,C)
xC
Move(A,x,B)
xB
Move(C,x,T)
On(A,B) ^ On(C,T) ^ On(B,x) ^ Clear(B) ^ Clear(C)
On(B,C) ^ On(C,T) ^ On(A,x) ^ Clear(A) ^ Clear(B) ? ?
Move(B,y,C)
yC
Move(A,y,B)?
On(C,T) ^ On(A,x) ^ Clear(A) ^ Clear(B) ^ On(B,y) ^ Clear(C)
INITIAL STATE: (if x=T and y= T)
Not relevant: has effect delete Clear(B)
bold – literal that was added to the predecessor
underline – goal is not satisfied by initial state

8. Planning Graph Example
Init(Have(Cake)
Goal(Have(Cake)  Eaten(Cake))
Action(Eat(Cake)
PRECOND: Have(Cake)
EFFECT: Have(Cake)  Eaten(Cake))
Action(Bake(Cake)
PRECOND: Have(Cake)
EFFECT: Have(Cake)
Missing from book
From Fig. 10.8, p. 380

9. GraphPlan
function GRAPHPLAN(problem) returns solution or failure graph  INITIAL-PLANNING-GRAPH(problem) goals  CONJUNCTS(problem.GOAL) nogoods  an empty hash table for t = 0 to  do if goals all non-mutex in St of graph then solution  EXTRACT-SOLUTION(graph, goals, NUMLEVELS(graph), nogoods) if graph and nogoods have both leveled off then return failure graph  EXPAND-GRAPH(graph, problem)
From Fig. 10.9, p. 383

10. Spare Tire Problem
Init(Tire(Flat)  Tire(Spare)  At(Flat,Axle)  At(Spare,Trunk)) Goal(At(Spare,Axle)) Action(Remove(obj,loc), PRECOND: At(obj,loc), EFFECT: At(obj,loc)  At(obj,Ground)) Action(PutOn(t, Axle), PRECOND: Tire(t)  At(t,Ground)  At(Flat,Axle), EFFECT: At(t,Ground)  At(t,Axle)) Action(LeaveOvernight, PRECOND: , EFFECT: At(Spare,Ground)  At(Spare,Axle)  At(Spare,Trunk)  At(Flat,Ground)  At(Flat,Axle)  At(Flat,Trunk))
From Fig. 10.2, p. 370

11. Spare Tire Planning Graph
From Fig , p. 384