Author: Christophe Theron
Date: 22:48:48 04/19/98
Go up one level in this thread
On April 19, 1998 at 22:49:28, Robert Hyatt wrote:
>On April 19, 1998 at 19:33:25, Fernando Villegas wrote:
>
>>Hi Amir:
>>I have just played my first game against Junior -the module in Fritz- at
>>a relatively serious rhythm, 40 in 60, game that I lost after 50 moves
>>of a very hard fight for him but specially for me, of course, otherwise
>>I would be the winner.
>>My first impression is that the expression fast searcher with which is
>>defined even by you in the cd-rom clip is somewhat misleading as much as
>>there is some ambiguity in the definition of what it is fast search in
>>the first place.
>>What I saw is that Junior reaches very very soon 12 ply, faster than
>>Fritz even if Fritz counts more nodes per second than Junior. Then, I
>>thought that the speed of search should not be automatically considered
>>like something equal to the count number, but to the ply number. In my
>>opinion Junior is fast because he goes very soon to very deep searches,
>>not because the great crunching of nodes he does to get that. I can
>>easily imagine an even faster computer in terms of nodes, but very slow
>>in terms of ply if the search is totally full-width, without any pruning
>>at all. In that case the very fact of exponential growing of the tree
>>would impede a deep search at all. On the contrary. I can imagine an
>>slow thinking machine -like the human brain- reaching very deep levels
>>of ply because of an exceedingly good pruning or selective search.
>>So, when we say that this or that program is fast searcher we are not
>>concluding the search of how that program is, as it seem to happens, but
>>just beginning with it. We don t advance even an step saying that a
>>program is fast searcher in comparison with another that supposedly is
>> knowledge searcher . If, as I think, fast search equals deep search,
>>then there is a pruning device, a selective criteria. And if there is
>>such thing, the key to understand the problem is not just to say how
>> fast the program is, but to insvestigate how the program do so deep
>>search.
>>So, dear Amir, why don t you tell us a little bit the way you get those
>>very deep searches?
>>Fernando
>
>
>
>he's answered this several times here. that "depth" is not the same
>as the "depth" other programs report. So you can't compare those
>numbers
>and get any meaningful information...
Yes. I think several programmers here know how to reach high depths
quickly. But they don't use all of these selection techniques, because
they noticed that the quality of the game was better without some of
them, even if the program doesn't go as deep.
Each programmer chooses the set of selections he wants to use. The
interesting thing is that you can apply a new selection algorithm over
another one. For example you can use "null move" and "futility pruning"
together. If a move is not pruned by "null move", it has another chance
to be pruned later by "futility".
Personnaly, I try to use selection algorithms that are very different
from each other. Because some of them use in fact the same basic idea.
For example, there are "null move" and "fail high reduction". They are
not exactly the same, but in fact are based on the idea that when you
reach a very good position and your opponent has no threat against you,
you can (more or less) safely ignore what happens next.
If you use both of them, I think you are overusing this good idea, and
you take too much risks in your selection. But it is nevertheless a
workable approach. If I use both algorithms, my program is able to reach
greater depths. But IMO it won't play better.
I suppose that Amir decided to use more selection algorithms that the
other programmers. Of course I cannot speak for him. But I'm not sure he
is going to explain what he does, anyway. :)
I must admit that I was completely stunned was I saw the depths Junior
was able to reach in Paris. Reaching 12 plies in a few seconds would
give any other program a very high ELO. But the price to pay to reach
these depths is that Junior cannot see everything within its horizon.
Which is confirmed, without disrespecting Amir's work at all, by the
fact that Junior is not 200 elo points above the other good programs.
This is just my opinion. I would of course really love to see Amir's
opinion. The only official source about Junior. If he his inclined to do
so, because it's true that he has already said some words about this.
For you Fernando: I think that when we speak here about "fast searchers"
we mean "programs that have a huge node per second ratio". When a
program is able to reach great depths quickly, I would say it is a "deep
searcher". I think we could discuss if we agree on these names or not,
so things could get more clear next time.
Christophe
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