Artificial Intelligence Search Algorithms Quiz

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Questions and Answers

What is the time complexity of the depth-first search as mentioned in the content?

  • O(b + l)
  • O(b^l)
  • O(l^b)
  • O(bl) (correct)

In depth-limited search, how can a cutoff be indicated?

  • By returning a solution
  • By returning the cutoff value (correct)
  • By returning the maximum depth reached
  • By returning the standard failure value

What does the diameter of the state space refer to in the context provided?

  • The total number of possible sequences to investigate
  • The maximum number of nodes in a search tree
  • The maximum number of steps to reach any city from any other city (correct)
  • The maximum depth of any goal node

Iterative deepening depth-first search gradually increases the limit starting from which number?

<p>0 (C)</p> Signup and view all the answers

What defines a problem formulation in a problem-solving approach?

<p>Four specific items including initial state and goal test (A)</p> Signup and view all the answers

In the context of recursive depth-limited search, what signifies that a solution has been found?

<p>Goal-Test passes (A)</p> Signup and view all the answers

Which of the following best describes a toy problem?

<p>An illustrative problem used to compare algorithm performance (A)</p> Signup and view all the answers

What type of search algorithm is depth-limited search a special case of?

<p>Depth-first search (D)</p> Signup and view all the answers

In the context of the Vacuum World example, what is the goal test?

<p>Testing whether all squares are clean (C)</p> Signup and view all the answers

What happens when the depth limit is reached in recursive depth-limited search?

<p>A failure is returned (D)</p> Signup and view all the answers

What is the primary benefit of using iterative deepening depth-first search?

<p>It can be more efficient than depth-first search for unbounded search trees (D)</p> Signup and view all the answers

What does the successor function represent in problem formulation?

<p>All possible action-state pairs from a given state (D)</p> Signup and view all the answers

Which statement about path cost is correct?

<p>Path cost considers the number of actions executed (A)</p> Signup and view all the answers

What is a characteristic of a real-world problem?

<p>It involves solutions that people actually care about (D)</p> Signup and view all the answers

In the 8-puzzle problem, what action can a tile perform?

<p>Slide into the adjacent blank space (D)</p> Signup and view all the answers

For the initial state 'at Arad', what would be an example of a successor state?

<p>Adjacent cities that can be reached via driving (C)</p> Signup and view all the answers

What is a defining feature of the BS Algorithm?

<p>It is effective when generating predecessors is easy in both directions. (B)</p> Signup and view all the answers

What type of problem does not allow the agent to sense its environment?

<p>Sensorless problem (A)</p> Signup and view all the answers

In a contingency problem, what role do percepts play?

<p>They provide new information regarding the current state. (D)</p> Signup and view all the answers

What characterizes an exploration problem?

<p>The agent has no prior knowledge of states and actions. (D)</p> Signup and view all the answers

In a sensorless problem, which of the following is true?

<p>The agent cannot determine its own location. (D)</p> Signup and view all the answers

Which term describes a state that an agent believes it to be in?

<p>Belief State (A)</p> Signup and view all the answers

What potential outcome can result from executing a 'Suck' action in a contingency problem?

<p>It may lead to a dirty carpet due to unforeseen circumstances. (B)</p> Signup and view all the answers

Which search strategy is considered complete if the branching factor is finite?

<p>Breadth-first search (A)</p> Signup and view all the answers

What does the hill-climbing search algorithm primarily do?

<p>Moves in the direction of increasing value. (A)</p> Signup and view all the answers

What happens when a hill-climbing algorithm reaches a local maximum?

<p>It gets stuck with no higher neighboring states. (D)</p> Signup and view all the answers

What are ridges in the context of hill-climbing search?

<p>A sequence of local maxima that are difficult to navigate. (B)</p> Signup and view all the answers

How does a plateau affect the performance of the hill-climbing algorithm?

<p>It can trap the algorithm in a flat local maximum. (A)</p> Signup and view all the answers

Why is hill-climbing sometimes referred to as a greedy local search?

<p>It grabs the best available neighbor without planning ahead. (C)</p> Signup and view all the answers

What does the function HILL-CLIMBING return?

<p>A state that is a local maximum. (A)</p> Signup and view all the answers

Which of the following is a potential drawback of the hill-climbing algorithm?

<p>It can get trapped in local maxima. (C)</p> Signup and view all the answers

What is typically replaced at each step in the hill-climbing algorithm?

<p>The current node with a neighbor having the highest value. (A)</p> Signup and view all the answers

What is the initial value of alpha during the start of the alpha-beta pruning algorithm?

<p>$- ext{∞}$ (D)</p> Signup and view all the answers

When can the alpha value be updated in the pruning process?

<p>When it is MAX's turn. (D)</p> Signup and view all the answers

At node B, what are the values of alpha and beta after evaluation?

<p>alpha = $- ext{∞}$, beta = 3 (D)</p> Signup and view all the answers

What condition must be fulfilled for a node to be pruned?

<p>Alpha must be greater than or equal to beta. (C)</p> Signup and view all the answers

What is the value of alpha at node E after its evaluation?

<p>$5$ (D)</p> Signup and view all the answers

What happens to the right successor of node E after pruning?

<p>It is not traversed. (C)</p> Signup and view all the answers

How does the value of alpha at node A change after evaluating node B?

<p>It changes to 3. (B)</p> Signup and view all the answers

What is the final alpha value at node F after evaluating its child nodes?

<p>$3$ (D)</p> Signup and view all the answers

What is the main characteristic of stochastic hill-climbing?

<p>It randomly selects among available uphill moves. (D)</p> Signup and view all the answers

How does simulated annealing differ from traditional hill-climbing methods?

<p>It accepts downhill moves based on probability. (C)</p> Signup and view all the answers

What is a potential drawback of a purely random walk in search algorithms?

<p>It can become stuck at local maxima. (C)</p> Signup and view all the answers

In genetic algorithms, how are successor states generated?

<p>By combining two parent states. (A)</p> Signup and view all the answers

What is the primary application of simulated annealing mentioned in the content?

<p>Factory scheduling. (A)</p> Signup and view all the answers

Why might an algorithm using hill-climbing be considered incomplete?

<p>It may get stuck on local maxima. (A)</p> Signup and view all the answers

What is the initial setup for a genetic algorithm?

<p>A random set of k individuals. (B)</p> Signup and view all the answers

What does the 'badness' of a move refer to in simulated annealing?

<p>The amount an evaluation function is worsened. (B)</p> Signup and view all the answers

Flashcards

Initial State

Describes the starting point of a problem. It defines the initial conditions of the environment.

Successor Function

A function that maps a state to a set of possible actions and their resulting states. It represents the possible transitions from one state to another.

Goal Test

A criteria used to determine if a solution has been reached. This criteria can be explicit, like reaching a specific location, or implicit, like achieving a certain condition.

Path Cost

A measure of the cost of a solution. It can be the number of actions taken, the distance traveled, or any other relevant metric.

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Solution

A sequence of actions that transforms the initial state into a goal state. This path fulfills the problem's objectives.

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Toy Problem

A simplified version of a real-world problem, designed to illustrate problem-solving techniques and compare performance of different algorithms. It's often used in research and development

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Real-World Problem

A problem derived from a real-world situation. It has practical applications and people care about finding its solutions.

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Vacuum World

A simple example of problem solving using a virtual environment. It involves cleaning up dirt in a two-location space, illustrating the concept of problem solving using states, actions, and goal tests.

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Sensorless Problem

A problem where the agent lacks any sensory information (e.g., location, object states). The agent must act blindly, and a solution is a predetermined sequence of actions.

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Contingency Problem

A problem where the environment's state is partially known, or actions have uncertain outcomes. Solutions are designed to handle different possibilities, often involving conditional actions depending on sensory information.

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Adversarial Problem

A specific type of contingency problem where the uncertainty is introduced by the actions of another agent (like an opponent in a game).

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Exploration Problem

A problem where the agent has no prior knowledge of the environment's layout, actions, or states. The agent must explore and learn as it goes.

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Belief State

A representation of an agent's belief about the possible states of the environment based on available information.

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Solution (Sensorless)

A sequence of actions pre-determined to achieve a goal in a sensorless problem, without adapting to sensory feedback.

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Solution (Contingency)

A plan in a contingency problem represented as a tree or a policy, branching based on sensory information and actions.

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Contingency Planning

The problem of adapting actions based on new information, especially in contingency problems, often requiring interleaving search and execution.

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Breadth-First Search

A search strategy that explores the search tree level by level, starting with the root node and expanding all nodes at a given depth before moving to the next level. It is complete for finite search spaces and optimal for cases where the path cost is a function of the depth of the goal node.

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Greedy Best-First Search

A search strategy that explores the search tree by expanding the most promising node first, typically based on a heuristic function that estimates the distance to the goal. It is not complete or optimal but can be very efficient for finding a solution quickly.

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A* Search

A search strategy that explores the search tree by expanding the node with the lowest estimated total cost, which combines the path cost so far with the heuristic estimate of the remaining cost to the goal. It is complete and optimal for admissible heuristics (that never overestimate the actual cost to the goal).

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Depth-Limited Search

A search strategy that explores the search tree depth-first but with a predetermined depth limit. It stops exploring a branch if it reaches the depth limit. It is not complete but can be more efficient than depth-first search for problems with large depth.

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Iterative Deepening Search

A search strategy that combines depth-first search with gradually increasing depth limits. It starts with a small depth limit and repeatedly increases it until a solution is found. It is complete, optimal for uniform cost problems, and generally more efficient than depth-first search for large depth problems.

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Backtracking Search

A search strategy that explores the search tree by backtracking from a goal node to the initial state. It is typically used for problems where the goal state is known in advance and the focus is on finding a path to the goal.

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Heuristic Search

A search strategy that explores the search tree by using a heuristic function to guide the search. It is not complete or optimal but can be very efficient for finding a solution quickly. It can explore multiple promising paths simultaneously.

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Graph Search

A search strategy that explores the search tree by maintaining a set of nodes to be explored, called an open list, and a set of nodes that have been explored, called a closed list. It expands the most promising node from the open list and adds its unexplored children to the open list. It avoids revisiting previously explored nodes.

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Simulated Annealing

A type of hill-climbing search where downhill moves can be taken. The probability of accepting a downhill move decreases exponentially with the cost of the move, allowing the algorithm to escape local maxima. It was employed extensively in solving VLSI layout problems in the early 1980s.

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Hill Climbing

A search algorithm used to find optimal solutions in a state space. In this method, the current state is replaced with a successor with a higher evaluation function value. It is guaranteed to be incomplete as it could get stuck in local maxima.

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Genetic Algorithm

A search algorithm where a descendant state is created by mixing two parent states. Each state is a string of characters, usually 0s and 1s, and the population of states starts with k randomly generated ones.

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Stochastic Hill Climbing

A type of hill-climbing search where a successor state is chosen randomly and the selection probability is influenced by the steepness of the uphill move, meaning better moves are more likely to be chosen.

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First-Choice Hill Climbing

A type of hill-climbing search where successors are generated randomly until an improved state is found. This method is known for its simplicity and efficiency.

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Random-Restart Hill Climbing

A method to overcome the local maximum problem in hill-climbing. It starts multiple searches from random states to increase the chance of finding the global maximum.

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Purely Random Walk

A random-walk search algorithm that is complete, meaning it guarantees finding a solution if one exists, but is very inefficient.

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Beam Search

A search algorithm where an initial set of candidate solutions are randomly generated and then through a series of steps like selecting, evaluating, and recombining, a better solution is iteratively created.

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Local maxima

A point in the search space that is higher than all neighboring points, but lower than the global maximum. Hill-climbing algorithms can get stuck here, unable to reach the optimal solution.

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Ridges

A sequence of local maxima, forming a 'ridge' in the search space. Hill-climbing algorithms struggle to traverse these ridges, as they get trapped at each local peak.

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Plateaux

A flat area in the search space where the evaluation function doesn't change. This can be a flat local maximum, preventing further progress, or a 'shoulder', where moving in a specific direction might lead to a better solution.

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Hill-climbing search

A search algorithm that continually moves in the direction of increasing value, aiming to reach a 'peak' where no neighbor has a higher value. It's a simple and common technique.

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Greedy local search

A greedy algorithm that focuses on choosing the best neighboring state without considering the future consequences. It often leads to good solutions but is prone to getting stuck at local maxima.

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Current State

The current state in the search process, representing the current position or configuration in the problem space.

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Evaluation function

A function that evaluates the quality of a state. It measures how good a particular state is, often measured as distance to the goal or cost of reaching it.

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Highest valued successor

The best neighboring state to the current state, offering the highest value or the lowest cost according to the evaluation function. This is the state selected for the next step in the hill-climbing process.

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Alpha-Beta Pruning

A pruning technique for searching tree-structured game spaces, such as those in chess or checkers, where the goal is to find the optimal move for the current player.

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Alpha Value

The best possible score that the maximizing player (MAX) can guarantee, given the current state of the game.

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Beta Value

The best possible score that the minimizing player (MIN) can guarantee, given the current state of the game.

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Pruning Condition

When the alpha value is greater than or equal to the beta value, it means that the current branch of the search tree can be ignored because there's no way it can lead to a better outcome than what's already known.

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Initial Alpha Value

The initial value of alpha is set to negative infinity (-∞), representing the worst possible outcome for the maximizing player.

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Initial Beta Value

The initial value of beta is set to positive infinity (+∞), representing the worst possible outcome for the minimizing player.

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Alpha-Beta Pruning Process

The algorithm starts by exploring the first possible move from the current state, and then recursively explores the resulting branches of the search tree, pruning branches that don't improve the current best score.

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Alpha-Beta Pruning Termination

The algorithm continues to prune branches until it reaches a terminal node (leaf) of the search tree or until the pruning condition is met. The best move for the current player is then selected from the remaining un-pruned branches.

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Study Notes

  • Problem solving involves finding a sequence of actions that lead to a desirable goal.
  • A well-defined problem includes an initial state, an operator (successor) function to determine possible next states, a state space representing all reachable states, a path through the state space, a path cost function, and a goal test to check for a goal state.
  • Search is a systematic method for examining states to find the path from the initial state to the goal state.

Search Space

  • The search space consists of all possible states and the operators that define the connections between them.
  • The output of a search algorithm is a solution, or a sequence of operations that leads from the initial state to a goal state.

Problem-Solving Agents

  • A problem-solving agent is a goal-based agent designed for tasks by finding a sequence of actions that satisfy the goal.

Toy Problems

  • Vacuum World Example: An agent is operating in a two-location world. The locations can contain or not contain dirt. Goal: All squares are clean.
  • 8-Puzzle: A 3x3 board with tiles and a blank space. Goal is to reach a goal state.
  • 8-Queens Problem: Eight Queens on a chessboard, no queen attacking another. Goal: Place all eight queens on the board.

Real-World Problems

  • Route Finding: Finding the shortest path between locations. Example: Find the best route from Arad to Bucharest in Romania.
  • Airline Travel: Finding the best route and time for travel.
  • Touring Problems: Visiting each city at least once.
  • VLSI Layout Problem: Arranging millions of components on a chip.
  • Robot Navigation: Generalizing route-finding, a robot can move in a continuous space, with an infinite set of possible actions and states.

Uninformed Search Strategies

  • Breadth-First Search: Expands nodes in increasing depth.

  • Uniform-Cost Search: Expands nodes with the lowest cost first. -Both strategies are complete but not always optimal.

  • Depth-First Search: Explores as far as possible along each branch before backtracking.

  • Depth-Limited Search: Depth-first search with a pre-defined depth limit.

  • Iterative Deepening Search: Repeatedly applies depth-limited search with increasing depth limits.

  • Best-First Search: Expands nodes based on an evaluation function (f(n)).
  • Greedy Best-First Search: Uses a heuristic function to estimate the distance to the goal (f(n) = h(n)).
  • A* Search: Combines cost from start to current node (g(n)) and heuristic cost to goal node (h(n)),(f(n) =g(n) + h(n)). A* Search is optimal and if the heuristic is admissible (never overestimates the true cost) then A* is optimal.
  • A* search is considered optimal among all algorithms because it never misses a better answer.

Local Search Algorithms

  • Hill Climbing: A greedy algorithm that moves towards increasingly better solutions.
  • Simulated Annealing: Stochastic algorithm combines greedy approach(hill-climbing) with random walk (expands any successor with probability, based on temperature).
  • Genetic Algorithms: Searches by generating a population of possible solutions, then selecting those with the highest evaluation function, and combines parts of the best to create new solutions.

Constraint Satisfaction Problems (CSPs)

  • A set of variables (X1, X2,…Xn) and a set of constraints (C1,C2,… Cm).
  • Each variable has a domain (possible values).
  • A constraint specifies allowed combinations of values for a subset of variables.
  • Goal: Find a complete assignment of values to variables that satisfies all constraints.
  • Example: Map Coloring, Cryptarithmetic, 8 Queens problem, etc
  • Games are competitive environments. Players' goals are in direct conflict.
  • Minimax Search: A game-playing algorithm.
  • Alpha-Beta Pruning: An optimization technique for minimax search that reduces the number of nodes evaluated.

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