• Create Account

Interested in a FREE copy of HTML5 game maker Construct 2?

We'll be giving away three Personal Edition licences in next Tuesday's GDNet Direct email newsletter!

Sign up from the right-hand sidebar on our homepage and read Tuesday's newsletter for details!

We're also offering banner ads on our site from just \$5! 1. Details HERE. 2. GDNet+ Subscriptions HERE. 3. Ad upload HERE.

# sectrix

Member Since 13 Jun 2012
Offline Last Active Jun 14 2012 05:17 PM

### Understanding the D* lite whitepaper

13 June 2012 - 04:14 PM

I'm writing a tool for a game I play, and I've found I need a good pathfinding algorithm.

I've already written an A* and a Dijkstra routine, but I've found them to be far too slow. It takes them about 20 and 13 seconds respectively to find the shortest path along the longer routes.

I've come across D* lite as a possible better solution, but there's very little information on the web. Some of what I did find came from here several years ago, so, here's to hoping those members are still around.

I found and read Koenig's 2002 paper about it, (this one), and I understand all of the LPA* pseudo code except for two lines:

- Calculate keys()
In the calculateKeys function, it reads: Return[ min( g(s), rhs(s) ) + h(s, sgoal) ; min ( g(s), rhs(s)) ]. What I don't understand is the ; in the middle. Does the function return two values? Does it perform some sort of operation on the results of the two min statements?

- Update vertex and rhs calculation
The other line I had trouble with was this one: min s' (is element of) pred(s) (g(s'), c(s', s)). I don't get that one at all. The s' in pred() with the smallest g or c?

I feel like I'm going to get a lot of blank stares, but, any ideas anyone?

PARTNERS