Artificial Intelligence By Mr. Ejaz CIIT Sahiwal

Different types and techniques for uninformed searching Lecture 4

Conversion from Graph to Tree

Tree Terminologies

The Two-One Problem

Solution space for two-one problem

Search Strategies Blind/Uninformed Informed/Heuristic Any path/Non-optimal Optimal Path search

Blind Search VS Heuristics

Simple Search Algorithm simple search algorithm that will try to give you an idea about the sort of data structures that will be used while searching, and the stop criteria for your search. Let S be the start state 1. Initialize Q with the start node Q=(S) as the only entry; set Visited=(S) 2. If Q is empty, fail. Else pick node X from Q 3. If X is a goal, return X, we’ve reached the goal 4. (Otherwise) Remove X from Q 5. Find all the children of state X not in Visited 6. Add these to Q; Add Children of X to Visited 7. Go to Step 2

Simple Search Algorithm Applied to Depth First Search Depth First Search dives into a tree deeper and deeper to fine the goal state. We will use the same Simple Search Algorithm to implement DFS by keeping our priority function as P(n)= 1/height(n) we will give priority to the element with minimum P(n), hence the node with the largest value of height will be at the maximum priority to be picked from Q.

Depth First Search

Applying simple search algorithm

Breadth First Algorithm Breadth First Search explores the breadth of the tree first and progresses downward level by level. Now, we will use the same Simple Search Algorithm to implement BFS by keeping our priority function as P(n) =height(n) We will give priority to the element with minimum P(n) hence the node with the smallest value of height will be at the maximum priority to be picked from Q.

Problems with DFS and BFS DFS can run forever in search spaces with infinite length paths. DFS does not guarantee finding the shallowest goal. BFS requires a great deal of space (exponential in depth)

Progressive Deepening Progressive deepening actually emulates BFS using DFS. The idea is to simply apply DFS to a specific level. If you find the goal, exit, other wise repeat DFS to the next lower level.