Questions tagged [heuristics]

Questions about algorithmic strategies that quickly solve a problem well most of the time, but give no guarantees.

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131 views

Early termination of A* with weak heuristic if solution is known

I have a large graph G and a pair of nodes s,t. I want to use the A* algorithm to find the shortest path from s to t, and I have a heuristic that is consistent. Suppose I already know of a path ...
3
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1answer
605 views

Global relabeling heuristic: Push-relabel maxflow

I have a correct, working implementation of the preflow-push-relabel maxflow algorithm [2]. I am trying to implement the global relabeling update heuristic [3], but have run into some issues. I have ...
3
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1answer
156 views

Unsplittable flow in capacitated networks

I have an undirected network with capacitated links/edges. Between some nodes unsplittable traffic has to be routed. All demands and capacities are known, but it is uncertain if all flows can be ...
3
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1answer
503 views

Mutation and crossover operations in discrete differential evolutionary operations?

I need to use discrete differential evolutionary algorithm for assigning discrete values from set size $L$ to vectors of size $D$ where $L$ could be smaller, equal or larger than $D$. Elements of ...
3
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1answer
359 views

Quick union and heuristic by size

Studying Quick-Find and Quick-Union heuristic I've found clear that: with quick find trees and a union based on the size of the trees we can make a union in $T_{am}(n)=O(\log(n))$ with quick find ...
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0answers
40 views

Defining preferred paths makes $A^*$ heuristic lose admissibility

In a geographical graph, where each edge's cost is equal to the physical distance between its nodes, one can be tempted to manipulate the cost of some of the edges, to make it a bit lower, in order to ...
3
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0answers
52 views

Heuristic for making set of indexes in an array/matrix with generating functions/patterns

I am trying to find a lead on how to solve or find a heuristic the following kind of problem: Given an array/matrix with entries of only 1s and 0s, using a set of looping functions/patterns of a ...
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0answers
367 views

Trying to understand the Gilmore-Lawler lower bound

For a class project we're developing a software that solves a common optimisation problem. After some research we've found out that our problem is called QAP (Quadratic Asssignment Problem) and the ...
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0answers
1k views

Time complexity 2-opt method

I'm doing a practice test for a course on routing problems. There's a question asking to infere the time complexity of the 2-opt method. I can see that the complexity per iteration is in $O(n^2)$ ...
3
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1answer
392 views

How to tell if a Heuristic is monotonic

I've applied a Heuristic to a puzzle where I need to move all off the B's the the right of the W's. my Heuristic is the total distance of the B's from the right most W's. my initial state is (B,B,B,*,...
2
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1answer
301 views

Are there practical methods for solving ILP?

Recently I encountered some papers in which the most important part seems to be writing an Integer Linear Program for a problem for which there exist some exact or heuristic algorithms! Is solving an ...
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2answers
1k views

Ant colony optimization for continuous functions

I am trying to do optimization of a voice activity detection function, which is a function with continuous parameters. This is easily accomplished with genetic algorithms, simulated annealing, and ...
2
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2answers
62 views

Does an optimal path imply the heuristic is admissible?

If we are given an A$^*$ path search with some heuristic $h$ that yields an optimal path, without knowing that the heuristic is admissible beforehand, would this imply that $h$ is admissible?
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1answer
3k views

Creating admissible heuristics from functions?

I'm having trouble figuring out how to create admissible heuristics from cost functions. For example, if I was trying to create an admissible heuristic from a cost function that takes in starting ...
2
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1answer
4k views

Algorithm A vs Algorithm A*: What's the difference?

I can find quite a bit of literature on A* but very little on A. What is the difference between the two search algorithms?
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2answers
58 views

A* without heuristic more efficient than Dijkstra

I am using the module networkx to operate on graphs made from OpenStreetMap. I wanted to compare the shortest path algorithm to ...
2
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1answer
70 views

Overall time complexity of Heuristical Algorithm for travelling salesman problem [TSP]

I am trying to figure out the time complexity of a heuristical algorithm used to solve the Travelling Salesman Problem in a more efficient way than by brute force, ($\theta(n!)$ or similar) The ...
2
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1answer
611 views

Is a two-opt move guaranteed to produce a non-worse tour?

I have a little doubt with respect to the two-opt improvement heuristic for TSP. I understand how it works, from the Wikipedia article on 2-opt and "Heuristics for the Traveling Salesman Problem". ...
2
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1answer
67 views

Is there a name for algorithms which detect nearly-similar structures?

I'm interested in how you might detect similarities in tree structures. For example, in these three JSON documents; ...
2
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1answer
4k views

Heuristic for sokoban puzzle problem

I am trying to write IDA* for Sokoban puzzle problem (http://en.wikipedia.org/wiki/Sokoban) but It seems that my heuristic is not so good for making the algorithm fast. My heuristic is to consider $h(...
2
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1answer
226 views

Solving AlienTiles with an A* heuristic

Hello I am trying to solve the AlienTiles problem described at alientiles.com using the A* algorithm but I cannot find any good heuristic function so far. In AlienTiles you have a board with $N \...
2
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1answer
200 views

Neighbourhood in local search metaheuristic

I cannot seem to find an answer to this question with Google, so I am going to ask here: is it required for a good neighbourhood function that it in principle (i. e. by recursively considering all ...
2
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1answer
3k views

Nilsson's sequence score for 8-puzzle problem in A* algorithm

I am learning the A* search algorithm on an 8-puzzle problem. I don't have questions about A*, but I have some for the heuristic score - Nilsson's sequence score. Justin Heyes-Jones web pages - A* ...
2
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1answer
140 views

SAT Solving + Turing Machines

I have a couple of questions based on how SAT solvers work. I understand that SAT solvers may employ any/all of the following techniques: Randomness Heuristics Backtracking SAT is just one example ...
2
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1answer
34 views

What is the number of degrees of freedom of my problem in this Simulated Annealing context?

I'm trying to apply a Simulated Annealing technique to solve my (NP-complete) optimization problem. I'm using this book to help myself out. In the section on Simulated Annealing and more specifically ...
2
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1answer
712 views

Difference between heuristic-based searching and optimal path searching

I'm currently studying for an AI computer-science course. One thing is difficult for me to grasp and somewhat vaguely explained in my course-material: I understand that with search-methods like e.g. ...
2
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1answer
809 views

Genetic algorithm fitness function [closed]

I'm trying to write some little code (POC for the selection/mutation operators) that uses a genetic algorithm to solve a global maximum for a function. ...
2
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2answers
8k views

Heuristic for Finding Multiple Goals in Graph - e.g. using Kruskals Algorithm

I'm a none-computer-science-student and get some knowledge on AI by taking the CS188.1x Course (Artificial Intelligence) on www.edx.org . Currently, I am working on the "Search in Pacman" Project; ...
2
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1answer
40 views

Why is the usual simulated annealing algorithm using a Boltzmann probability?

I've coded a personal version for the simulated annealing problem, and I was wondering why, (other than by analogy to the physics), the probability is $$ p = e^{-\dfrac{\Delta \text{length}}{T}}$$ (...
2
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1answer
78 views

Does domination rule apply for inadmissible heuristics?

Let's say $h_1(n) \geq h_2(n)$ so that dominance is established even if $h_1$ and $h_2$ are both inadmissible/non-optimal heuristics -in whichever given search space. Is $h_1$ still faster/better ...
2
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1answer
50 views

Why do admissible functions allow $A^*$ to retain correct shortest path computations?

I was reading about how to use $A^*$ and was told that: A heuristic is admissible if $h(u) \leq \delta(u,t)$, where $\delta(u,t)$ function indicates that the shortest path from $u$ to $t$. I was ...
2
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1answer
270 views

Informed search with a lower-bound heuristic?

I am well aware of informed graph / tree search strategies for optimal solutions when one has an admissible heuristic - i.e. one that never overestimates the minimum cost from a node to any goal state....
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2answers
169 views

Heuristic for Tournament Scheduling

I am holding a bi-yearly tournament in my city, for which I want to write a program that gives me (nearly-)optimal pairings, and waiting time. The setup is as follows: ...
2
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0answers
49 views

Matching of two weighted graphs allowing one-to-many mapping

I am looking for a heuristic for a graph matching problem as follows. Given two graphs: $A$ (consisting of nodes $a_i$) and $B$ (consisting of nodes $b_i$). Typically the size of $B$ is larger than ...
2
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0answers
63 views

Are there many empirical results about which metaheuristics are well-suited for which problem domains?

One of the nice things about genetic algorithms is that they can easily be used for a diverse array of problem domains, whereas PSO for example seems best-suited for candidates of real-valued vectors (...
2
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0answers
438 views

Simulated Annealing for graph coloring

I am working on a simulated annealing algorithm for graph coloring. The model I follow is the following: http://riad.pk.edu.pl/~zk/pubs/PPAM07_2.pdf. I have troubles understanding the cooling schedule ...
2
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1answer
944 views

AI: Heuristic function A* search

I have an assignment in my university where I have to implement Uniform Cost Search and A* Search. We have an input which includes a map and queries. The map is weighted, directed graph, represented ...
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0answers
58 views

How to compare A* with DP approach in finding shortest Path?

Consider a hypercube defined over $n$ dimensions where the edges are associated to strictly positive weights, and nodes are marked with $n$ bit-strings, e.g. the source is marked as (0,0,0) in a 3-...
2
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0answers
174 views

Experimental Survey on Different Heuristics for Knapsack Problem

I am looking for a good survey/study of experimental results of heuristics for Knapsack problem (or implemented libraries in java/c++). Any help is appreciated!
2
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0answers
119 views

Heuristics for tree decomposition into k shortest paths

What kind of heuristics are useful in a tree decomposition of a graph to find the k shortest paths from a given source to a vertex? Moreover, the local shortest paths at each node in a tree are ...
1
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2answers
3k views

When does the nearest neighbor heuristic fail for the Traveling Salesperson?

Can you provide an example of NN algorithm failure on the Euclidean traveling salesman problem? I was trying to construct a specific example of this for my friends and was failing.
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2answers
59 views

Choosing heuristic for A* algorithm where cost is less than absolute distance

Looking for information on choosing a heuristic for instances where the cost of traversing an edge can be less than one. For example, say movement is allowed in the cardinal directions. Should all ...
1
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1answer
888 views

Heuristics for the $n$-puzzle

An admissible heuristic for an n-puzzle is the Manhattan distance. Now if the cost of a transition is equal to the number of the piece that is moved, is it true that the Manhattan distance is still an ...
1
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1answer
691 views

Implement multi-fragment heuristics for the traveling salesman problem

I would like to implement the multi-fragment heuristics algorithm for finding a solution to the traveling salesman problem. The algorithm is described here as follows: This seriation method re-...
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1answer
288 views

Why do heuristic functions only approximate the real value of the cost?

As stated in the title I'm wondering why do heuristic functions only approximate the real value of the cost? I understand it can never overestimate, but can it ensure the cost is accurate?
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1answer
244 views

How do I compute this non terminal positions evaluation, for tic-tac-toe?

Looking at this solution on page 3 but having trouble understanding the evaluation function specifically. For non terminal positions, we use a linear evaluation function defined as Eval (...
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2answers
863 views

Heuristics & Constrain Satisfaction Problem Differences

I'm currently taking an Algorithms course, and we are covering Backtracking, CSP, and heuristics. However, I'm getting confused on exactly the differences between these terms and their applications. ...
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1answer
31 views

What is the peak in fitness landscape

I have just started reading about fitness landscapes and I couldn't understand what the peak means. What does the peak mean?
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1answer
2k views

How does the nearest insertion heuristic for TSP work?

In my theoretical computer science class and we were covering "Heuristics". In it we covered "Greedy Heuristics" for the "Vertex Cover Problem", "Interval Scheduling" and the "Traveling Salesperson ...
1
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1answer
333 views

If h(n) is a perfect heuristic (that is, h(n) = h*(n)), then does it imply that A* will always take linear time complexity?

That is, if h(n) = h*(n), then A* only expands nodes that lie on an optimal path to the goal. But does this imply that A* will always take a linear time in the solution length to find an optimal ...