Author: Stuart Cracraft
Date: 21:13:54 09/18/04
Go up one level in this thread
On September 18, 2004 at 19:43:55, Andrew Platt wrote:
>On September 18, 2004 at 15:45:57, Sune Fischer wrote:
>
>>On September 18, 2004 at 15:22:35, Uri Blass wrote:
>>
>>>I do not wait with the pv copying and it is one of the things that I may change
>>>in the future but I do not understand why waiting is a problem.
>>
>>Waiting is not "a problem", it just means that you can't reset the length of the
>>PV when you enter a new node. You would be deleting information that has not yet
>>been copied up the tree.
>
>Perhaps your logic works differently but that's not the case in a standard AB
>implementation. If your logic looks like this:
>
> Score = -AlphaBeta (..., Ply + 1);
>
>then you are always starting a new ply and you aren't losing any information. In
>fact, if you don't do this you have a problem because you have information
>relating to a *previous* move in the PV. Resetting the PV at this ply won't
>cause the information already backed up from the previously tried moves.
>
>My routine looks something like this
>
>AlphaBeta ()
>{
> // Try to get a cutoff with a null move
> if (TryNullMove ())
> {
> return Score;
> }
>
> // Try to get a hash table cutoff
> if (HashTableCutoff ())
> {
> return Score;
> }
>
> // We're going to search moves. Reset this ply in the triangular array
> PV [Ply] [Ply] = Ply;
>
> while (GetMove ())
> {
> MakeMove ();
> Score = -AlphaBeta (..., Ply + 1);
> UnmakeMove ();
>
> if (Score > Alpha)
> {
> if (Score >= Beta)
> {
> return Score;
> }
>
> // Update the Principal variation now we have a better move
> UpdatePV ();
> }
> }
>
> return Score;
>}
>
>
>Make sure you reset the PV if you cutoff, etc. too.
Thanks for the exposition/code -- But what is "reset the PV if you cutoff?"
The cutoff I see is in
if (Score >= Beta)
{
return Score;
}
but I see no resetting the PV in there???
>
>Andy.
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.