Author: Tom Kerrigan
Date: 13:03:26 05/25/03
Go up one level in this thread
On May 25, 2003 at 09:41:48, JW de Kort wrote:
>On May 25, 2003 at 08:03:46, Tom Kerrigan wrote:
>
>>On May 25, 2003 at 07:53:59, JW de Kort wrote:
>>
>>>Hi friends,
>>>
>>>My chess engine currently has two search related problems.
>>>
>>>1) Sometime a e.g. 8 ply search only returns a pv a say 4 or 5 or sometimes even
>>>only one move. Can this be a result of using the hashtable?
>>
>>The obvious possibility is that there was contention for the hash table entry
>>that would have contained the rest of your PV. There may be additional
>>explanations too.
>>
>>>2) The engine searches until a certain amount of time is spend. If the search
>>>notices that the time has ran out, the search is stopped an beta is returned. I
>>>think this is the correct thing to do. BUT the following happens: sometimes a 8
>>>or 9 ply search is done and a correct move (at least a correct move in the eye
>>>of my engine) is found but then suddenly a completely different move is
>>>selected, most of the cases this is a blunder and often the evaluation drops
>>>with about the score of a bishop because a bishop is lost. It is nice to have
>>>written a enging playing like a human, but i would rather remove this problem.
>>
>>When time runs out, my program just stops searching and doesn't try to do
>>anything clever that might be wrong. After every call to search, I check
>>stop_search, and if it's TRUE, I return 0...
>>
>>-Tom
>
>Thanks Tom,
>
>i do not quit get what you mean. Suppose the engine has reached a depth of 4 ply
>and time runs out. Then some value has to returned to depth 3. I use beta for
>this. How do you solve this problem?
I return 0, but it doesn't matter what value you return, because that value
won't be used for anything. Every call to search looks like this:
x = -search(-beta, -alpha, depth - 1);
if (stop_search)
return 0;
if (x > alpha) {
etc.
So when time runs out, your entire search tree "collapses" without updating
anything (like the PV) so your program will play whatever the best move was
right before it ran out of time, as it should...
-Tom
This page took 0 seconds to execute
Last modified: Thu, 15 Apr 21 08:11:13 -0700
Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.