Author: Robert Hyatt
Date: 06:34:33 10/26/98
Go up one level in this thread
On October 26, 1998 at 01:36:59, Nobuhiro Yoshimura wrote: >On October 25, 1998 at 19:34:32, Robert Hyatt wrote: > >>On October 25, 1998 at 18:58:12, Nobuhiro Yoshimura wrote: >> >>>On October 22, 1998 at 23:20:10, Robert Hyatt wrote: >>> >>>>On October 22, 1998 at 23:04:31, Peter McKenzie wrote: >>>> >>>>>On October 22, 1998 at 21:38:29, Fawna Bergstrom wrote: >>>>> >>>>>>Well everyone has their opinions on this kind of question--here are a few of >>>>>>mine. Let's go back to basics: >>>>>> >>>>>>Level I: You search full-width to a fixed depth (alpha-beta, iterative >>>>>>deepening, etc. are all assumed, of course.) Here your evaluator includes both >>>>>>material and positional factors. Move ordering is critical. First expand >>>>>>"killer" moves, "interesting" moves and moves that yield a higher evaluation. >>>>>> >>>>>>Level II: If you like you can then search beyond that looking at "interesting" >>>>>>moves such as captures, threats, checks, etc. Don't bother with threats unless >>>>>>the threatened piece is hanging and/or more valuable than the threatening piece. >>>>>> You should limit the depth of this second phase or you can skip it altogether >>>>>>and go straight to level III--it's your call. In level II the evaluator >adjusts >>>>>>for material only. Personally I wouldn't waste too many plies on Level II. >>>>> >>>>>I'm not 100% sure what you mean here, but if you start returning scores from the >>>>> quiescence search that don't take into account changes in evaluation due to >>>>>captures effecting pawn structure, and these scores can find their way into your >>>>>PV, then you're likely to get killed positionally. >>>>> >>>> >>>> >>>> >>>>there are things interesting to try here. IE if you only look at winning >>>>captures, you can probably get away with a positional eval at the leaf node >>>>that starts the qsearch, and then pass this value along to be modified as >>>>pieces are captured. >>>> >>> >>>May I ask a simple question ? I am a Japanese-Chess programmer so that >>>I donot much about the chess programming. In the following postion: >>> 0) In the q-search node >>> 1) WTM >>> 2) a white in danger >>> >>>Questions: >>> 1) Do you generate esacaping moves for the white peice ? >>> 2) Do you assume that a white piece can esacpe in the stand pat eval? >>> 3) Is it better to make a "PASS" move ( without depth deductions) >>> to check whether the black can really gain profit by capturing it? >>> >>> >>>Nobuhiro >>> >>> >> >>I don't, no. I don't trust the q-search to do this sort of stuff. I only hope >>I have extended enough already to avoid this problem. >> >>(2) yes as my eval doesn't consider pieces that are trapped/hung/etc except for >>some special cases like a bishop at h2 with a pawn at g3 trapping it... >> >>(3) did this in the 1970's and it worked ok... ie "pass" then see what happens, >>and *then* try to find a move that prevents that from happening... >> >>Don't do it today because of the extreme depths we see nowadays... > >In a position like: > 0) in q-search node > 1) WTM > 2) white queen in danger > 3) a black pawn in danger > >In such postion, do you only generate a capturing a black pawn? >If so, the postion will be evaluted as a very bad position( losing queen). >Are you saying that if we search deep enough, we donot get >a bad side effect eventhough such position might occurs during the search? I'm only saying that after looking at all the games I have studied carefully, I haven't seen a single game that was decided by some sort of failure in the q-search. Maybe because I didn't search quite deeply enough, or because I mis-evaluated something... but not because the q-search broke... but in the above case, I would simply not capture the black pawn. I would first call Evaluate() to produce the stand-pat score, then try the capture. At the next ply my opponent captures my queen and returns that score. I decide that doing nothing is better than grabbing the pawn and losing my queen, the idea being that instead of grabbing the pawn I can save the queen. Which doesn't seem to cause problems except in rare cases where a piece is really trapped and it doesn't realize this...
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