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Subject: Re: Mate in 1 - but Fritz 6 needs 1 hour!!!

Author: Colin Frayn

Date: 02:17:29 08/13/00

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On August 12, 2000 at 16:22:37, Adrien Regimbald wrote:

>You're completely missing the point here.  If you want to guarantee that you
>have correctly ascertained if there is a mate in <x> from any given position,
>you need to do a brute force search up to depth <x>, possibly depth <x+1>
>depending on how you do mate detection.

OK, so I don't use guesswork pruning by default and that was what I was
measuring the speed decrease relative to.

However, the method still applies to those who do pruned searches, except you
can't guarantee finding the CM all the time.  However, you still will succeed
occasionally and the pruning benefit will be substantial.  In the position
posted earlier, you _have_ to order all the moves at ply 1, so you'll definitely
find the mate immediately every time.

>If you aren't talking about doing brute force searches, then you aren't
>guaranteeing you see all the short mates, in fact you can be missing mates all
>over the place.

Agreed.  I don't use guesswork pruning algorithms so that I know my analysis is
correct. My method applies whatever searching algorithm/pruning you employ.  I
use pv-enhanced negamax with a-b and hash tables etc... and so I can guarantee
to see every mate down to a certain ply.  You don't have to do brute force - a-b
pruning is tactically sound.

All I'm claiming is that my method reduces the search time by a negligible
amount *regardless of algorithms employ to actually do the search* and it
occasionally results in enormous speed increases.

Take this position for example;

[D]4Q3/2p3p1/7p/p1k1B3/2p1P2P/2P3P1/1r2q3/6K1 w - -

which ColChess searches *fully* to depth 13 ply in just over 3 seconds on my
p3-450.  It is a mate in 9.  Crafty sees the mate quite early because of its
advanced extensions, but after 30 seconds had still only just reached 11 ply in
its search.  There are probably better examples where Crafty can't see the mate,
and I unfortunately can't remember the board setup before this position, which I
know to be one of them.

>If you are talking about doing brute force searches, then you're an absolute
>genuis,

*g*

Cheers,
Col



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