In addition to what Nice Coder has said, if you look at the bottom of this page, they show one example of a Node and what it stores in A*.

A* assumes that the map is something which is known in maths as a "graph". This is not a wiggly line drawn on a sheet of graph paper as you might imagine, but instead of set of "nodes" connected with things called "edges".

Think of it as a stick-and-ball model (like in Chemistry), where the nodes are the balls and the edges are the sticks.

Of course A* is usually used where the map is very regular, hence is a continuous (either square or hex) grid of nodes, each connected to 4 (or 6) of its neighbours by edges.

This is the most useful application of A*, beause it allows the heuristic to be calculated usefully and cheaply.

Mark

from what ive read this term applies to problem spaces outside of pathfinding aswell....... i think :S

good old wiki :) it's example is better because it's not reffering to a specific lanauge (this A* thing or what ever it is)

(this description will allow you to visualize a node tree in your head)
A node is best visualized as a sphere, and this sphere can produce a "branch", a branch is best seen as a straight line.

Lets have 3 spheres, node A, node B.
( -> means to)
node A has a branch that attaches to node, A->B, this branch could also be seen as going B->A.

this in programming means that A has a variable that contains the location of point be (usualy a pointer to it or some way of naming and accessing B), this allows us to move from A to B.

If we want another node we creat that node and creat a branch to it from either A or B (having a branch from A and B to C is also possible)

lets show this with ASCII art :D


Step 1. no branch (most likely B was just created)

A     B

step 2. branch A->B

A---B

now A can see B and B can see A

step 3. creat C

A---B             C

step 4. branch B->C

A---B---C

now we can go from A to C if we go through B, but this may not be what we want so we make a branch to C from A, other wise to get to see we need to folow this path A->B->C.

step 5. branch from A->C

A----B\    / \  /  \/  C

We now have 3 "nodes" each node can hold what ever you wish, for a basic brute force AI I'm making I use tree nodes to keep track of clicks on a grid, each click is a node and contains the state of the graph it was in, each branch off of a node represents what happend when we made that click and what we can do, we then branch off of that node, and creat nodes attached to it the represetn possible clicks (this is described a bit better mabe worse in my collapse post).

A more classic "node" tree is a binary tree, each node spawns 2 nodes.

node 1 has 2 nodes

those 2 have 2 each

and so forth

usualy deciding where to go in this tree/what to create in this tree is done with a conditional check:

at node 1: if A > B put A in node 2, else put in node 3

rise and repeat :)

also imagining a tree fractal helps:
http://id.mind.net/~zona/mmts/geometrySection/fractals/tree/treeFractal.html

big post hope it wasn't to long.

Quote:Original post by MDI
A real life example of this is the graph denoting "who can see who". A is behind a one way mirror with B in front of it. A can see B, but B cannot see A (B can see itself).

I'm a big fan of the "guy walking off a cliff" example of that =]