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Subject: Nolot Bxh7 and deep thought/deep blue

Author: Vincent Diepeveen

Date: 07:02:08 01/12/00


Let's have another thread about the Nolot positions.
>
>Here are my results as of now:
>
>   DT     Ferret
>          4x450
>   ------ ------
>1  6hr
>2  2min   31sec
>3
>4  2.5hr
>5  2hr
>6
>7  6hr
>8
>9  9min
>10 2min   11sec
>11 5min   48sec

Let's zoom into position #8 not found by Deep Thought

r3rbk1/ppq2ppp/2b1pB2/8/6Q1/1P1B3P/P1P2PP1/R2R2K1 w - - bm Bxh7; 8

This position is of course in nolot as PC programs don't extend such
lines too deeply. Just like the other nolots it only has to do with
king safety and a lot of forced moves around the king.

[c] ==> check extension
[s] ==> singular best move extension
[f] ==> forced move (a forced move is singular too) extension

the TACTICAL line needed to find Bxh7:

Bxh7+     Kxh7[c]
Qh5+      Kg8[c]
Rd4[s]    gf6[f]
Rg4+[s]   Bg7[c]
Qh6[s]    Kf8[f]
Rxg7      Rec8
Qxf6      Be4[f]     (otherwise rh7-h8 mate)
Rae1[s]   Bf5[f]
g4[s]     Bxc2[f]
Rxe6[f]   Bd3
Rg6[c]    Qc1+
Kh2[c]    Qc7+
f4[c]     Qc2+
Kg3[c]    <any legal move>
Qh8 mates in quiescencesearch.

So totally 10 plies don't carry an extension and therefore need
to be seen by brute force search depth.

Note that diep is already positive for white after Rxe6, but
score is not high enough for white to change to Bxh7 in the root,
as diep is *very* happy anyway with this position.

Diep evaluates after Rg6 the position as +1.598 for white.

Now you can tell me a lot of crap about singular extensions, but
if you search 7 ply and use singular extensions as described by Hsu,
then you need just 7 ply to find Bxh7.

If Deep Thoughts eval is a bit worse than DIEP's, like mainly counting
pawns, then it needs an additional few ply. It needs another 3 ply
to see the checking sequence, so it totally needs 11 ply then to
see the Bxh7 trick with a score of over +10.0.

If it doesn't do checks in quiescencesearch
then it needs 11 ply totally to find this combination.

Vincent





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