Author: KarinsDad
Date: 13:01:09 07/25/00
Go up one level in this thread
On July 25, 2000 at 14:10:36, John Coffey wrote: >I don't think that the goal is to play like a 1200. Instead it is to be >able to fine tune the ability of the computer. If the computer is only >looking at 512 nodes, it might not drop a piece, but it will not see past ply >3 in the middle game and it will be beatable. > Node limitation is similar to ply limitation. It is not as crude a scale, but it is the same insufficient concept. Node count is exponential up the tree. 2 ply brute force results in 1260 nodes generated for an average 35 move per side position. 2 ply is probably 1200 strength (assuming the same evaluation function). So, the computer would not just hang a piece, but it could easily lose in a simple combination. 3 ply in a similar position might suddenly play real bad though. Why? Because it would hang a piece for a pawn sometimes. [D]5rk1/1n1n1ppp/8/2p5/8/2QN4/5PPP/5RK1 w - = - = - r k = = n = n = p p p - = - = - = - = = - p - = - = - - = - = - = - = = - Q N = - = - - = - = - P P P = - = - = R K - Nxp nxN Qxn and not realize nxQ since it would not search 4 ply. The number of brute force nodes at ply 3 would be 44,000. Approximately 35 times as many nodes would be searched, but the program would play weaker than the 2 ply version which would avoid the Nxp move due to losing the knight. Now, I know that you will claim that this search does not result in a quiescent position, hence, the example is not valid due to extensions, etc. But, the reason for this example is to illustrate that the program HAS to have some level of control over it's search, or it could return bogus information and make an extremely bad move at 3 ply that it would not at 2 ply. So, the 1200 rated version of the program would play worse than the 1400 rated version. Time limits, node limits, and even ply limits all have the same inherent type of problem. They pick the best move found SO FAR, regardless of whether the search got interrupted or not. And in order to gradiate the scale, you do not want to limit the search and HOPE for a tactical or positional mistake that a given rated player can take advantage of in order to play at a similar rating as the computer is set at. Instead, you want the program to play tactically, positionally, and strategically inferior to it's normal powerful strength. Even something as limiting the opening book to the first 4 moves does not mean that the program won't play book until move 10. But that will rarely happen with a 1200 rated player. Do you understand the difference? You have to have the program determine what it's best x moves are at a given position and pick one of them based on some function (maybe random, maybe not, probably some sort of bell curve since even the worst player in the world can accidentally make the best move on the board) of the rated level that the program is set at. This is a much better way to attempt to gradiate the scale in a reasonable manner since time, node count, and ply count while picking the best move each time results in more artificial looking play. KarinsDad :)
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