Channels ▼


Ant Colony Algorithms

Source Code Accompanies This Article. Download It Now.

Emergent Behavior

ACOs are a simple example of how simple systems can self-organize or show emergent behavior. Emergent behavior is not a well-defined term, but generally refers to complex and unexpected outcomes arising from the interaction of simple individual entities. Examples include bird flocking, creation of complex nests by colonies of termites, and (more controversially) structure in human societies, particularly economics and financial markets.

In this article, I construct a colony of virtual ants with a set of deliberately simplified abilities. After describing and setting up a simple mechanism by which these ants can communicate, I'll demonstrate how this virtual colony can solve a classic problem from operations research—the infamous Traveling Salesman problem.

The Traveling Salesman Problem

The Traveling Salesman problem asks: Given a set of towns that a salesman has to visit, and the distances between each, what is the shortest tour that takes him or her to each town just once, ending up at the starting point?

This type of problem is NP-complete, which is mathematical jargon for "hard." With a small number of towns, it's feasible to try every possible route, but when the number increases, an exponential rise in the computations is required. A brute-force approach for any but the smallest tours requires unfeasibly large amounts of computer power and time.

For real problems, it's not always necessary to get the best solution; a good one is just as useful if it can be found in a short time. The ACO described here gives very good solutions to a test problem in a matter of seconds. And this is useful; the TSP is closely related to a number of important real-world problems in scheduling and design, so a solution to one can quickly be applied to others.

Related Reading

More Insights

Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.