On 24-Jun-09, at 10:18 PM, Andrew Hunter wrote:
More to the point, however: you don't want more precision. Welcome to the world of numerical algorithms; floating point arithmetic is inherently inexact. Get used to it. For example, I'll bet your errors are caused by testing for equality against zero, and if I had to guess, you're probably trying to terminate a procedure when some value hits zero? It's not going to; you need to introduce the concept of tolerances, and accept if |val| < tol. This is a simplistic solution and not really right in most cases, but might help. If you want more advice about how to handle floating-point inaccuracy, could you provide a program and what's going wrong?
What I'm specifically working on is a maze generator. The generator is based on Prim's algorithm: starting with a graph containing a single node, I connect new nodes to existing nodes that are not surrounded yet until I've reached a specified number of nodes in the graph. In my case, the maze is on a hexagonal grid. There are no boundaries around the maze, so the generator may attach hexagonal cells, or nodes, from any side (I don't particularly care if the generator sometimes makes one long hallway). Each hexagonal cell is represented in the graph as a co-ordinate representing the cell's centre. I have a function that takes a co-ordinate and returns a list of co-ordinates representing the centres of the adjacent cells. Keeping track of the hexagons' positions is important because these mazes will be levels for a game I hope to somehow put together; the potions would be used for drawing the maze and for AI pathfinding. When adding a new node/hex to the graph/maze, I pick an existing node and get all of its neighbour co-ordinates, filtering out co-ordinates that represent nodes already present in the graph. The problem is that, due to floating point errors, these co-ordinates are not be exact. If hex A has the co-ordinate for hex B in its list of adjacent hexes, hex B would not necessarily have the co-ordinate for hex A in its own list. Things get mismatched quickly.