Author: Robert Hyatt
Date: 10:12:02 10/02/98
Go up one level in this thread
On October 02, 1998 at 09:19:40, blass uri wrote:
>
>On October 02, 1998 at 08:35:58, Robert Hyatt wrote:
>
>>On October 02, 1998 at 02:06:33, blass uri wrote:
>>
>>>
>>>On October 02, 1998 at 02:03:05, blass uri wrote:
>>>
>>>
>>>>I understand that tablebases can help to see long mates(instead of material
>>>>evaluation of 2 pawns advantage) but I do not understand how can they help in
>>>>the original position because the static evaluation without hash tables
>>>
>>>I mean without tablebases
>>>
>>>Uri
>>
>>
>>because the positions after rxb2 are lost for black, while the starting
>>position is -1.something... I'm not sure what it is you don't understand.
>>The tablebases provide -MatNN, +MatNN and Draw scores... and this has
>>nothing to do with the static evaluation of the position. A tablebase
>>hit overrides *any* score.
>
>I understand that tablebases provide -MatNN,+MAtNN and draw scores
>but I do not understand how can you go to positions that you use tablebases
>at depth 12 from the initial position because tablebases are for KPP against K
>or KP against KP and not for positions with more pieces.
>You need to calculate more than 16 plies to go to positions that you can
>use tablebases if you do not do special extensions in pawn endings.
>
>I thought that If you can see by tablebases that the position is -MatNN because
>it is KPP against K then you can see without tablebases that the position is not
>-0.xx because the static evaluation function without tablebases is not -0.xx
>
>Uri
You are misunderstanding how I use them. Imagine a position with KBN vs K.
You understand that in that position, crafty will play perfectly, and will win
with the KBN side, correct?
IE in this position:
+---+---+---+---+---+---+---+---+
8 | *K| | | | | | | |
+---+---+---+---+---+---+---+---+
7 | | | | | | | | |
+---+---+---+---+---+---+---+---+
6 | | | | | | | | |
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | | | | | | | |
+---+---+---+---+---+---+---+---+
2 | | | | | | | | |
+---+---+---+---+---+---+---+---+
1 | K | B | N | | | | | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
crafty promptly says Kb2 Mat25... ok so far...
now lets modify the position to this:
+---+---+---+---+---+---+---+---+
8 | *K| *R| *Q| | | | | |
+---+---+---+---+---+---+---+---+
7 | | | | | | | | |
+---+---+---+---+---+---+---+---+
6 | | | | | | | | |
+---+---+---+---+---+---+---+---+
5 | | | | | | | | |
+---+---+---+---+---+---+---+---+
4 | | | | | | | | |
+---+---+---+---+---+---+---+---+
3 | | R | | | | | B | |
+---+---+---+---+---+---+---+---+
2 | | | | | | | | |
+---+---+---+---+---+---+---+---+
1 | K | B | N | | | | | |
+---+---+---+---+---+---+---+---+
a b c d e f g h
In this position. crafty says Be4+ Mat34, with a 2 second search. How did
it do that? like this:
8 2.03 Mat34 1. Be4+ Ka7 2. Bxb8+ Ka6 3. Bb7+ Qxb7
4. Rxb7 Kxb7 <EGTB>
8-> 3.27 Mat34 1. Be4+ Ka7 2. Bxb8+ Ka6 3. Bb7+ Qxb7
4. Rxb7 Kxb7 <EGTB>
What it did was to search deeply enough to see that it could trade bishop
and rook for the opponent's rook and queen, leaving it in a KBN vs K position.
And after searching the 8 plies into the future (as it did above) it then found
the endgame database position and said "aha, Mate in N from this point."
This is why my current version (15.21) won't play Rxb2, because it can see
deeply enough into the future to see the white king eating the black pawns
and that gives "mate in N". Or in some variations it sees one black and one
white pawn being traded, and that also leads to mate in N.
The point is that I do the egtb probes *deeply* in the search, so that after
a series of trades, I can recognize, *before* I start the series, that I end up
in a won, lost or drawn ending...
Hope that helps...
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