Lecture 3 : Uniformed Search Method

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Questions and Answers

What is the main characteristic of uninformed search methods?

They are always more efficient than heuristic search methods.

They are only used for bidirectional search.

They have no knowledge about the cost from the current state to the goal. (correct)

They use a heuristic function to estimate the cost to the goal state.

What is the purpose of node expansion in search?

To select the next node to consider.

To generate all successor nodes considering the available actions. (correct)

To return the solution when the goal state is reached.

To avoid repeated states in the search.

What is the fringe or frontier in search?

The set of nodes that have been expanded.

The set of nodes that have been considered but not expanded.

The set of nodes that are not relevant to the search.

The set of nodes that are waiting to be expanded. (correct)

What is the main goal of a search strategy?

To define which node is expanded next. Signup and view all the answers

What is the difference between a blind and a heuristic search method?

Blind search methods have no knowledge about the cost to the goal, while heuristic search methods have access to extra information. Signup and view all the answers

What is the route finding problem in search?

Finding a path from the initial node to the goal node. Signup and view all the answers

What is the main function of a General search Algorithm?

To provide a broad framework for doing search Signup and view all the answers

What is the main difference between Uninformed and Informed search strategies?

Uninformed search has no knowledge about the cost, while Informed search has access to extra problem-specific information Signup and view all the answers

Which data structure is convenient to use when implementing Breadth First Search (BFS)?

Queue Signup and view all the answers

What is the main characteristic of Breadth First Search (BFS)?

Expands the shallowest nodes on the fringe first Signup and view all the answers

What is the purpose of the Explored list (also known as Closed list) in a search algorithm?

To store expanded nodes Signup and view all the answers

What is the name of the search strategy that detects when a goal state has been found, but has no knowledge about the cost from the current state to the goal?

Uninformed search Signup and view all the answers

What is the primary factor that affects the time complexity of an algorithm, according to Table 5.1?

The size of the input (n) Signup and view all the answers

What is the primary concern of the space complexity criterion when evaluating a search method?

The amount of memory required to perform the search Signup and view all the answers

According to the evaluation of BFS, what is the time complexity of the algorithm?

O(b^d) Signup and view all the answers

What is the primary advantage of an optimal search strategy?

It finds the highest quality solution when there are multiple solutions Signup and view all the answers

What is the relationship between the time complexity and space complexity of BFS, according to the evaluation?

Time complexity is equal to space complexity Signup and view all the answers

What is the definition of the branching factor in the context of BFS?

The maximum number of successors of any node Signup and view all the answers

What is the main advantage of using bidirectional search over unidirectional search?

It reduces the time complexity Signup and view all the answers

What is the condition for stopping the bidirectional search?

When the two searches meet Signup and view all the answers

In a bidirectional search, what is required to search forwards from the start state?

A way to compute the successors of a node Signup and view all the answers

What is the relationship between the number of nodes examined in a unidirectional BFS search and a bidirectional BFS search?

The number of nodes examined in a bidirectional BFS search is the square root of the number of nodes examined in a unidirectional BFS search Signup and view all the answers

What is the notation for the set of all nodes that are successors of a node n?

succ(n) Signup and view all the answers

What is the main limitation of using bidirectional search?

It requires a way to compute the successors and predecessors of a node Signup and view all the answers

What is the purpose of asymptotic analysis in the context of algorithms?

To compare the running time of different algorithms without considering constants Signup and view all the answers

What is the primary characteristic of the 'size of input' in the context of algorithms?

The length of the sequence being processed Signup and view all the answers

What is the definition of t(n) in terms of basic operations?

t(n) = 2n + 1 Signup and view all the answers

What is the purpose of the 'worst-case analysis' in asymptotic analysis?

To approximate the running time of an algorithm Signup and view all the answers

Study Notes

Problem Solving: Uninformed Search

Uninformed search methods are blind or brute force, having no knowledge about the cost from the current state to the goal.
Heuristic search methods, on the other hand, have access to extra problem-specific information, typically an estimate of the cost of getting from the current to the goal state.

Route Finding Problem

The route finding problem involves finding a path from an initial node to a goal node.

General Search

General search involves the following steps:
- If the current state is a goal state, return the solution.
- Apply all applicable operators to the current state, generating a new set of states (node expansion).
- Decide which state to consider next, and continue from Step 1.

Terminology

Fringe or frontier: The collection of generated nodes waiting to be expanded.
Node expansion: Generating all successor nodes considering the available actions.
Search strategy: Defines which node is expanded next.
General search algorithm: Fringe or open list contains generated nodes yet to be expanded, and the explored list or closed list contains expanded nodes.

Search Strategies

Uninformed (blind or brute force) search strategies:
- Breadth-First Search (BFS)
- Depth-First Search (DFS)
- Depth-Limited Search (DLS)
- Iterative Deepening Search (IDS)
- Uniform Cost Search (UCS)
- Bidirectional Search (BS)
Heuristic (informed) search strategies have access to extra problem-specific information.

Uninformed Search Strategies

Breadth-First Search (BFS):
- Expands the shallowest nodes on the fringe first.
- Expand all nodes at depth d before expanding any nodes at depth d+1.
- Data structure: Convenient to use a queue to implement BFS.
Mathematical analysis of algorithms:
- Asymptotic analysis involves finding a parameter that characterizes the size of the input and a measure that reflects the running time of the algorithm.
- Comparing algorithms involves finding the worst-case time complexity.

Comparing Algorithms

Asymptotic analysis: t(n) is in O(g(n)) if t(n) ≤ c * g(n) for some c and n0, and for all n > n0.
Comparing algorithms involves comparing the time complexity, considering only the highest-order term.

Criteria for Evaluating Search Methods

Time complexity: How long does it take to find a solution?
Space complexity: How much memory does it need to perform the search?
Completeness: Is the strategy guaranteed to find a solution when there is one?
Optimality: Does the strategy find the highest-quality solution when there are several different solutions?

Breadth-First Search (BFS)

Time complexity: O(b^d), where b is the branching factor and d is the depth of the goal node.
Space complexity: O(b^d), since each generated node being part of the fringe must be saved in memory.
Optimality: UCS will find the optimal solution.

Bidirectional Search

Runs two simultaneous searches: one forward from the initial state and the other backward from the goal state, stopping when the two searches meet.
Motivation: Reduce the time complexity by searching in both directions simultaneously.
Time complexity: O(b^(d/2)), where b is the branching factor and d is the depth of the goal node.
Space complexity: O(b^(d/2)), since each generated node being part of the fringe must be saved in memory.
Optimality: Bidirectional search can find the optimal solution.
Additional considerations: Need a way to compute the successors of a node for forward search and the predecessors of a node for backward search.

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Description

Test your understanding of uninformed search methods, including blind search and brute force methods, such as Breadth-First, Depth-First, Depth-Limited, Iterative Deepening, and Uniform Cost. Learn how to compare and differentiate between various search methods. This quiz covers the basics of problem-solving strategies and their applications.