# Questions tagged [search]

For questions involving search algorithms and their use in artificial intelligence

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### Is N the total number of nodes in the frontier plus the number of nodes in the explored list?

I'm studying fundamentals of AI from the classic Russell-Norvig book (3rd edition). I have a small doubt about the effective branching factor, which is defined as follows (section 3.6.1, p. 103): One ...
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1 vote
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### How to find the order in which DFS algorithm will inspect the nodes?

I have been taking Artificial Intelligence course in College. I came upon this problem. Now here I have to find the order in which DFS algorithm inspects the nodes and what is the path from Start to ...
180 views

### Why is depth-limited is preferable to minimax without depth limited

I have read about a question that says the following: Why is depth-limited minimax preferable to minimax? One of the wrong answers was: The depth-limited minimax will achieve the same output as ...
1 vote
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### Best algorithm for the Word Ladder puzzle

What would be the best performing algorithm to solve the Word Ladder problem, in terms of guaranteed finding of the shortest solution in the shortest possible time? Is it BFS, DFS, A*, IDA* or another ...
58 views

### Where can I find Norvig's version of the pseudocode for the A* search algorithm?

Can anybody point me to a link to Peter Norvig's version of the A* pseudocode. I've googled it interminably but found nothing. It's the version that uses the Unexplored/Frontier/Explored data ...
41 views

### Hierarchical Navigable Small World Graphs : Expected Number of Steps in a Layer

Paper: Efficient and robust approximate nearest neighbor search using Hierarchical Navigable Small World graphs In the Search Complexity section, the author estimates that the expected number of steps ...
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### What is the relationship between classical searching algorithms in AI and machine learning?

I think the relationship between the local search algorithms in AI for continuous spaces and Machine Learning is somewhat clear, as most of these search algorithms use gradient-based methods for ...
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### Is there an error in A* optimality proof Russel-Norvig 4th edition?

In "AI: A Modern Approach", 4th edition, by Russell and Norvig, they give a purported proof that A* is cost-optimal for any admissible heuristic. The given proof seems most certainly wrong. ...
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### How DFS may expand the same state many times via different paths in an acyclic state space?

I am reading the book titled Artificial Intelligence: A Modern Approach by Stuart Russell and Peter Norvig (4th edition) and came across this sentence about depth-first search (page 79, line 12): For ...
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### How do the BFS and DFS search algorithms choose between nodes with the "same priority"?

I am currently taking an Artificial Intelligence course and learning about DFS and BFS. If we take the following example: From my understanding, the BFS algorithm will explore the first level ...
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### What does "unknown search spaces" mean in the context of Evolutionary Algorithms?

In the article Multi-Verse Optimizer: a nature-inspired algorithm for global optimization (DOI 10.1007/s00521-015-1870-7), it's written The results of the real case studies also demonstrate the ...
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### What is an efficient way to implement an contextual search for a search engine?

So I am working on a search engine and want to implement a contextual search for my search engine but would like to get some advice before I start working on it. I have a basic knowledge of A.I. like ...
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### Are ranking models considered discriminative?

I'm developing a model that ranks entries based on cosine similarity to a query. Since it doesn't actually define a boundary between x and y I initially believed that such ranking models are not ...
1 vote
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### How do I create the search tree for DFS applied to a grid map?

I have been working through some search tree problems and came across this one: Assume that that the algorithm has a closed list and that nodes are added to the frontier in the following order: Up, ...
66 views

### Is $\min(h_1(s),\ h_2(s))$ consistent?

If $h_1(s)$ is a consistent heuristic and $h_2(s)$ is a admissible heuristic, is $\min(h_1(s),\ h_2(s))$ consistent?
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### What would happen if we set the evaluation function in the best-first search algorithm as the cost of paths taken to new nodes?

I am reading Artificial Intelligence: A Modern Approach. In Chapter 3, Section 3.3.1, The best-first search algorithm is introduced. We learn that in each iteration, this algorithm chooses which node ...
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### Does a differential evolution algorithm mutate its population during a generation?

I'm implementing a differential evolution algorithm and when it comes to evolving a population, the page I am referencing is vague on how the new population is generated. https://en.wikipedia.org/wiki/...
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### Are hill climbing variations always optimal and complete?

Are hill climbing variations (like steepest ascent hill climbing, stochastic hill climbing, random restart hill climbing, local beam search) always optimal and complete?
1 vote
431 views

### Determining minimal state representation for maze game

I came across this question set. It asks following question: Let’s revisit our bug friends from assignment 2. To recap, you control one or more insects in a rectangular maze-like environment with ...
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### Is there any situation in which breadth-first search is preferable over A*?

Is there any situation in which breadth-first search is preferable over A*?
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### Incorrect node expansion in game board with A* search

I have the following game board below, and we're using A* search to find the optimal path from the agent to the key. There are 8 directions. Up, down, left, right have a cost of 1, and diagonal ...
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### What is the difference between the heuristic function and the evaluation function in A*?

I am reading college notes on state search space. The notes (which are not publicly available) say: To do state-search space, the strategy involves two parts: defining a heuristic function, and ...
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### Why do we use the tree-search version of breadth-first search or A*?

In Artiﬁcial Intelligence A Modern Approach, search algorithms are divided into tree-search version and graph-search version, where the graph-search version keeps an extra explored set to avoid ...
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### When does IDA* consider the goal has been found?

I was reading about IDA* and I found this link explaining IDA* and providing an animation for it. Here is a picture of the solution. I know what is the cutoff condition (it depends on F), and the ...
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### What is the difference between the uniform-cost search and Dijkstra's algorithm?

Every computer science student (including myself, when I was doing my bachelor's in CS) probably encountered the famous single-source shortest path Dijkstra's algorithm (DA). If you also took an ...
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### Why is the completeness of UCS guaranteed only if the cost of every step exceeds some small positive constant?

I was reading Artificial Intelligence: A Modern Approach 3rd Edition, and I have reached to the UCS algorithm. I was reading the proof that UCS is complete. The book state that: Completeness is ...
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### If uniform cost search is used for bidirectional search, is it guaranteed the solution is optimal?

If uniform cost search is used for both the forward and backward search in bidirectional search, is it guaranteed the solution is optimal?
1 vote
528 views

### What is the space complexity of bidirectional search?

Is the space complexity of the bidirectional search, where the breadth-first search is used for both the forward and backward search, $O(b^{d/2})$, where $b$ is the branching factor and $d$ the length ...
1 vote
2k views

### What is the space complexity of breadth-first search?

When using the breadth-first search algorithm, is the space complexity $O(b^d)$, where $b$ is the branching factor and $d$ the length of the optimal path (assuming that there is indeed one)?
1 vote
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### What is the space complexity of iterative deepening search?

When using iterative deepening, is the space complexity, $O(d)$, where $b$ is the branching factor and $d$ the length of the optimal path (assuming that there is indeed one)?
1 vote
209 views

### How does the MCTS tree look like?

I have come across the Monte Carlo tree search (MCTS) algorithm, but I can't find what the tree should look like. For example, does it still represent a minimax process, i.e. player 1 from the root ...
1 vote
32 views

### Which method of tree searching should be used for this board game?

Suppose the following properties of a board game: High branching factor in the beginning of the game (~500) which slowly tends towards 0 at the end of the game Evaluation of the any given board ...
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### Why is depth-first search an artificial intelligence algorithm?

I'm new to the artificial intelligence field. In our first chapters, there is one topic called "problem-solving by searching". After searching for it on the internet, I found the depth-first ...
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### Is A* with an admissible but inconsistent heuristic optimal?

I understand that, in tree search, an admissible heuristic implies that $A*$ is optimal. The intuitive way I think about this is as follows: Let $P$ and $Q$ be two costs from any respective nodes $p$ ...
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### How does best-first search differ from hill-climbing?

How does best-first search differ from hill-climbing?
1 vote
462 views

### Which heuristics guarantee the optimality of A*?

The following is a statement and I am trying to figure out if it's true or false and why. Given a non-admissible heuristic function, A* will always give a solution if one exists, but there is no ...
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### Doesn't the number of explored nodes with IDA* increase linearly?

I think I'm misunderstanding the description of IDA* and want to clarify. IDA* works as follows (quoting from Wiki): At each iteration, perform a depth-first search, cutting off a branch when its ...
1 vote
167 views

### Can we solve an $8 \times 8$ sliding puzzle using hill climbing?

Can we solve an $8 \times 8$ sliding puzzle using a random-restart hill climbing technique (steepest-ascent)? If yes, how much computing power will this need? And what is the maximum $n \times n$ that ...
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### What is a example showing that the tree-based variant for the greedy best-first search is incomplete?

I understand that a tree-based variant will have nodes repeatedly added to the frontier. How do I craft an example where a particular goal node is never found. Is this example valid. On the other ...
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### Wooden railway search problem AI

I have this problem. A basic wooden railway set contains the pieces shown in Figure 3.32. The task is to connect these pieces into a railway that has no overlapping tracks and no loose ends where a ...
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### What is the difference between hill-climbing and greedy best-first search algorithms?

While watching MIT's lectures about search, 4. Search: Depth-First, Hill Climbing, Beam, the professor explains the hill-climbing search in a way that is similar to the best-first search. At around ...
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### 2 Partition Problem

I want to solve the two partition problem (https://en.wikipedia.org/wiki/Partition_problem) using an uninformed search algorithm (BFS or uniform cost). The states can be represented by three sets S1,...
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### How can I apply the alpha-beta pruning algorithm to the "1-2 steal marbles" problem?

I have the following problem called "1-2 steal marbles". Initially, there are 6 marbles on the board. One of the players can choose to remove 1 or 2 marbles leaving 5 or 4. After that, the other ...
158 views

### How can I formulate a nonogram problem as a constraint satisfaction problem?

I've just started learning CSP and I find it quite exciting. Now I'm facing a nonogram solving problem and I want to solve it using backtracking with CSP. The first problem that I face is that I ...
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