Author: Robert Hyatt
Date: 06:32:12 09/28/98
Go up one level in this thread
On September 27, 1998 at 19:39:38, Serge Desmarais wrote: >On September 21, 1998 at 18:23:50, Robert Hyatt wrote: > >>On September 21, 1998 at 15:13:41, John Coffey wrote: >> >>>On September 21, 1998 at 14:58:33, John Coffey wrote: >>> >>>>If on the otherhand I search the first move that wins a piece, and all but one >>>>of my opponents responses regains material, then I could do a null move after >>>>all but one of my opponent's responses, thus saving close to 80 or 90%. Maybe >>>>this is the piece of the puzzle that I am missing? >>>> >>>>Thanks for the response. Best wishes, >>>> >>>>John Coffey >>> >>>Errr... maybe not. If all but one of my opponents moves fail to regain a piece >>>then doing a null move will effectively gives the other side two moves in a row >>>and then they can regain the piece anyway, thus defeating the null move. So >>>the null move must work when the opponent has no threats at all. It is hard >>>for me to see this happening often enough to get such a dramatic *exponential* >>>reduction in the tree size. >>> >>>Again I will take your word for it. I am assuming that we only try the >>>null move when we have gained material? This is what I have read, but maybe >>>you try null moves at other times? If so then this would make more sense >>>to me. >>> >>>John Coffey >> >> >>I try them _everywhere_ in the search, before trying any other move. The idea >>is that if your opponent can't take two moves in a row and crush you, your >>position is overwhelming and doesn't need any further searching to prove that >>it is probably winning... > > > >But what if it is a quiet and blocked position with both sides moving behind >their respective lines and with most pieces on the first rank at one time or >another? Then, even giving 1 or 2 free shots to your opponent, he would not be >able to really hurt you seriously in anyway, except by moving a pawn and >breaking open a line, at worst winning a pawn? > > >Serge Desmarais that's the point, however. There are practically *no* positions in chess where playing two moves in a row wouldn't result in winning something. IE if we played a game where I could make two moves in a row once, I'd expect to beat you every time. In your case, you can't put your queen on a square where it can be attacked in one move, because that's when I'll use my two moves, once to attack it, once to rip it. You can't put your king on a square where I can attack and then mate using two moves. In tree searches, this most commonly happens when one side is way down in material and even giving him two moves in a row he can't regain enough to get back to equal. In endgames, this doesn't work as well, because with no pieces on the board, such double-move threats are less serious (they do exist, but we don't do null- move when there are no pieces).
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