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A heuristic graph-search algorithm for finding shortest paths. The input to A* is a starting node, the goal node, plus a heuristic function h that returns an estimate of the distance from a given node to the goal node. If the heuristic h never overestimates the distance to the goal, then it is called an admissible heuristic. A* search with an admissible heuristic is guaranteed to find the shortest path between the starting node and the goal node. A* is the darling of ArtificialIntelligence courses, probably mostly because it’s relatively easy to understand the proof of this fact. Furthermore, it can be shown that an algorithm which visits fewer nodes then A* could potentially miss the shortest path.

A* works by visiting one new node at time. It keeps a PriorityQueue full of nodes, and always "expands" the node with the lowest priority (sometimes called its f-value, or expected cost) which is computed as cost(node) + h(node), where cost(node) is the distance travelled so far, and h(node) is the heuristic estimate of the remaining distance to the goal node. Every time a node is "expanded", its unexplored neighbours are added to the queue. The result is that A* keeps track of a large number of potential paths radiating from the start node, and it extends these paths one node at time, always extending the one with the smallest cost(node) + h(node) value.

A* is an example of a GreedyAlgorithm. It is very similar to DijkstrasAlgorithm, the difference being that DijkstrasAlgorithm uses no heuristic, and so when deciding which node to expand next it only considers the cost from the start node.

Please mail to get a copy of the delphi unit.

Yesterday Ive found a great site with very useful online tools needed for every website programmer. Beside the tool that was posted yesterday (gradient maker) the site offers also following tools:

Image Optimizer
Use this tool to easily optimize regular gifs, animated gifs, jpgs, and pngs, so they load as fast as possible. Furthermore, convert from one image type to another.

FavIcon Generator
Generate a favicon using any regular image with this tool. A favicon is a small, 16×16 image that is shown inside the browser’s location bar and bookmark menu when your site is viewed.

Email Riddler
Email Riddler is an online tool that encrypts and transform your email address into a series of numbers when displaying it on your web site, making it impossible for spammers to harvest it from your site.

.htaccess Password Generator
Use this tool to generate all the necessary codes needed to password protect a directory or selects files within it on your site using .htaccess.

Gradient Image Maker
Gradient images are used everywhere in web page design, such as the background of form buttons, DIVs, to act as shadows etc. This tool lets you easily generate a gradient image.

.htaccess Banning Generator beta
This tool generates for you the necessary .htaccess code to ban visitors based on their IP address, block traffic originating from certain domains, or disable hotlinking on the desired file types on your server, such as images.

Button Maker
Use this tool to easily create those popular 80×15 micro buttons you see on web sites everywhere.

You can find these tools here: http://tools.dynamicdrive.com/

"Gradient images are used everywhere in web page design, ie, as the background of form buttons, DIVs, to act as shadows and other interesting visual effects etc. We created this online tool to allow you to painlessly generate a gradient image of 3 types, with instant previewing so you get exactly what you had in mind. Enjoy!"

If you want to create your own gradient image please visit: http://tools.dynamicdrive.com/gradient/