Author: Robert Hyatt
Date: 05:53:14 02/10/99
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On February 10, 1999 at 01:54:25, KarinsDad wrote: >On February 09, 1999 at 22:59:52, Robert Hyatt wrote: > >>On February 09, 1999 at 20:09:12, KarinsDad wrote: >> >[snip]> >> >>one of the big 'time savers' is what happens _below_ a sacrifice for nothing. >>Qxp pxq. And now no matter what two moves white plays in a row, black's >>position is still 'good' and everything below such moves gets trimmed away >>instantly... > >Ok. So in a given position (ply 0), there may be 5 captures (maybe even 10) that >are real losers (ply 1). For each of these, I would quickly find a response (ply >2, e.g. pxq). To do a null move, I would have to check about 36 reponses (on >average, not endgame) by white followed by 36 responses by white (i.e. all legal >moves at ply 3 and all legals moves as if it was still white's move at ply 4) >for a total of 36 + 1296 or 1332 generated legal moves (37 calls of the legal >move generator) and 1332 evaluations (but possibly not a full evaluation). > >If any of the "ply 3" or "ply 4" null moves lead to check, do you have to search >on? And what do you do with the "ply 3" check where you are doing null move, so >that black cannot move out of check before the "ply 4" null move? Do you just >ignore it? > >In a situation without the check (not knowing the answer yet), you pruned 10 >lousy moves (although there was no guarantee that qxp, pxq didn't lead to mate >in 3 or more) and there are 26 left which are also null prune checked, but they >do not fail, so their children can be searched and pruned normally. Correct? > >KarinsDad > the search below a 'null-move' is just like any other search. It is subject to the normal extensions, additional null moves may be tried (although not on the _next_ ply as two nulls in a row are not allowed) and so forth. Null move is simply an algorithm that recognizes when a part of the tree is hopeless for one side or the other, and it causes such sub-trees to be searched very quickly. >> >>IE with a full-width search, there are _many_ captures that are losers. Null >>move reduces the depth below these moves and make dismissing them quick and >>easy... >> >>>KarinsDad :)
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