Author: Mike Adams
Date: 21:14:34 09/21/00
Here is the position Pulsar is white in this fen string and to move.
1k4r1/ppp4R/3p4/4p3/q1n1P3/1NP5/P1P2rPP/1K2Q1R1 w - -
It is a forced mate in 6 but to make it even easier for chess engines to
see this position requires a queen sacrafice on move 3 to delay it to move 6
otherwise its mate in 4. Pulsar should need depth 5 to see this. It doesnt
process that it is in check in qsearch so after 4 moves its checkmated but it
can pass on moving in qsearch and be blind to the mate. My check extensions dont
help eathier because they look at if position is in check before move and it is
not in check or actually checkmated tell its move 5 for pulsar. Of course the
game is over then. Pulsar reported depth 6 in this position so it should have
seen it but instead it grabbed the free rook and reported a winning position
even though it had fallen into a forced mate in 6. So i did some tests.
With Null move at R2 (depth-3) Pulsar plays Qxr untill depth 7 then it plays Kb1
to Ka1.
With Null move at R1 (depth-2) Pulsar plays Qxr untill depth 6 then it also
plays Kb1 to Ka1.
With Null move off Pulsar plays Qxr untill depth 5 as expected then on depth 5
it plays Knight B3 to d4.
Whats the deal? Why is Pulsar missing a mate in 6 when it should see it in
depth 5 and it gets depth 6. Am i doing something wrong with Null Move? Is
there some trick to prevent this. I would be interested in a explanation of how
this can happen and if it happens often.
thanks Mike Adams
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Last modified: Thu, 15 Apr 21 08:11:13 -0700
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