Author: Christophe Theron
Date: 16:56:10 07/05/02
Go up one level in this thread
On July 04, 2002 at 22:23:34, Robert Hyatt wrote:
>On July 04, 2002 at 12:10:26, Christophe Theron wrote:
>
>>On July 04, 2002 at 10:07:37, Robert Hyatt wrote:
>>
>>>On July 04, 2002 at 03:49:40, Uri Blass wrote:
>>>
>>>>On July 03, 2002 at 14:29:17, Robert Hyatt wrote:
>>>>
>>>>>On July 03, 2002 at 13:46:17, Christophe Theron wrote:
>>>>>
>>>>>>On July 02, 2002 at 20:20:37, Robert Hyatt wrote:
>>>>>>
>>>>>>>On July 02, 2002 at 18:54:49, Keith Evans wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>Sorry to be anal retentive, but that's a bit of a stretch. Here's what they say:
>>>>>>>>
>>>>>>>>"The chess chips optionally support the use of an external FPGA (Field
>>>>>>>>Programmable Gate Array) to provide access to an external transposition table,
>>>>>>>>more complicated search control, and additional terms for the evaluation
>>>>>>>>function. In theory this mechanism would have allowed the hardware search to
>>>>>>>>approach the efficiency and complexity of the software search. Null move search
>>>>>>>>was also explicitly supported by this method. Due to time constraints, this
>>>>>>>>capability was never used in Deep Blue."
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>Read on. On page 67, section 4.1, item 3, "mate threat".
>>>>>>>
>>>>>>>"It is relatively simple using a null move search to detect if there is a
>>>>>>>threat in the current position.... The Deep Blue implementation ...
>>>>>>>
>>>>>>>Which matches what I said. They had support for a normal null-move search
>>>>>>>had they wanted to use it, but they did use null-move to detect threats,
>>>>>>>something that has been done before (and several of us use a form of mate
>>>>>>>threat extension based on this idea presently).
>>>>>>>
>>>>>>>So they used null-move in at least one way, without using it as a forward
>>>>>>>pruning algorithm, which fits with Hsu's "no errors in the search" theme he
>>>>>>>mentioned repeatedly over the years. Extra extensions were one thing to him,
>>>>>>>but outright errors were something else not to be tolerated. Right or wrong.
>>>>>>>I obviously disagree about the errors in a normal null-move search, but I
>>>>>>>can hardly argue with their success...
>>>>>>
>>>>>>
>>>>>>
>>>>>>That's my point as well.
>>>>>>
>>>>>>I don't argue about their success.
>>>>>>
>>>>>>I'm just saying that they succeeded because their chips were very fast. So fast
>>>>>>that they allowed them to use inferior search techniques and still succeed.
>>>>>>
>>>>>
>>>>>Could you not make the _same_ statement about chess 4.0 in 1975? Until that
>>>>>point _everybody_ was doing forward pruning like mad. They discovered that a
>>>>>a shallower full-width search had fewer errors and they stomped everybody into
>>>>>the ground until everyone converted...
>>>>
>>>>It is different.
>>>>It is obvious that selective search from the first plies
>>>>is a mistake when you have speed.
>>>>
>>>>It also seems obvious that pruning rules that are based
>>>>on the remaining depth is a good idea and you can use them
>>>>and see everything if you search deep enough.
>>>>
>>>>Uri
>>>
>>>
>>>Everybody is overlooking an _important_ detail, so lets take this back to
>>>CS101:
>>>
>>>1. Forward pruning is a form of selective search. You cull moves you think
>>>are no good, so that the rest are basically "extended" or searched deeper than
>>>the "lemon" moves.
>>>
>>>2. Search extensions do _exactly_ the same thing. They extend the moves you
>>>think are "good" so that they are searched more deeply, while the ones you
>>>do not extend are not searched that deep.
>>>
>>>In simple terms, the two ideas are _identical_ in every way, as far as the
>>>final result. To say that doing a full-width search with lots of very
>>>sophisticated extensions is not as good as doing a sophisticated selective
>>>search (forward pruning) is not a particularly sensible statement to make.
>>>
>>>_anybody_ that has spent any time on tree-searching will realize that _either_
>>>will produce _exactly_ the same result assuming the extensions and forward-
>>>pruning are done with the same skill level.
>>>
>>>So picking on this aspect of deep blue is simply a strawman argument. They
>>>clearly do more extensions than the rest of us. Which _may_ offset their
>>>lack of forward pruning. Believing or claiming anything else shows a lack
>>>of understanding of something...
>>
>>
>>
>>In this case, claiming that you are doing brute force just because you do not
>>want errors in your search is also a lack of understanding.
>>
>>Didn't Hsu say this? Aren't you repeating his words every time you can?
>
>So?
>
>
>>
>>First your point is that they have picked brute force because they had enough
>>power and did not want mistakes in the search, and now you are saying that they
>>had a selective search and that it is equivalent to what can be achieved with
>>strong pruning.
>
>I said the two results can be _identical_. This is covered in most good
>AI books that talk in any detail about minimax search...
>
>
>
>
>>
>>Thinking about it, it seems that you can indeed get the same search enveloppe by
>>either pruning or extending.
>
>
>:) As I said...
>
>
>>
>>But thinking twice about it, I think that it is not possible with the search
>>extension techniques used in Deep Blue to get something equivalent to the simple
>>and efficient pruning techniques we know today.
>
>
>Based on what?
Based on the description they have made of it.
>I _despise_ hearing that kind of statement with _zero_
>testing to support it. Very similar to the "bitmaps can't do this or
>that" statements that show up from time to time. And which I find very
>amusing as a bitboard practitioner.
I think you don't get what I said.
I'm just saying that given their framework (which is described in their
publication) one cannot get a search enveloppe equivalent to the enveloppe you
get with currently known pruning techniques.
I'm not talking here about the superiority of one system on the other.
You were talking about the classic idea that one can get the same search
enveloppe with either pruning or extensions.
Actually there is no discussion here. It is true, in theory.
That started to make me think about: "how can I get the same enveloppe by using
extensions instead of pruning" (in Chess Tiger for example).
And suddenly I find myself thinking about ideas I had never met before.
Here I'm not trying to oppose your ideas. Actually I have forked out of the
initial discussion about Deep Blue.
>Their search definitely "worked". That seems to be all that counts in the
>game of chess. Wins and losses..
>
>
>
>
>>
>>I smell that there is something important behind this and I will have to think
>>more about it. That's an interesting research area.
>>
>>
>
>It is also well-known. The two approaches are totally complementary. Same
>final result. Totally different ways of getting there.
That's what I wanted to say.
For example you are at 5 plies before the horizon and decide to stop searching
here.
What is the equivalent of this when one is using extensions?
In other terms, can the definition of extensions be expanded to cover both
"classical extensions" schemes AND pruning?
I'm always interested in generalizations, as they can help to uncover new ideas.
I don't remember having read a paper on this.
>>>As far as your selective search comments, It is obvious (to me) that everybody
>>>is not doing selectivity just deeply in the tree. It is being done near the
>>>root as well, based on some very trivial oversights that some programs make from
>>>time to time. Oversights that a 4 ply full-width search would see.
>>
>>
>>
>>It's not as simple as that.
>>
>>"Near the root" can mean several different things.
>>
>>You can apply some kind of gross pruning system near the root and make big
>>shortsighted mistakes.
>>
>>You can also apply some detection near the root and collect information to prune
>>later. Then you don't make such big mistakes.
>>
>>The argument that pruning will make obvious blunders sometimes is simply wrong.
>
>That argument is provable. Several have shown positions that Tiger simply
>can not see. The last one posted here you replied "the forward pruning
>simply misses that..."
Yes I remember.
It was Fernando using Chess Tiger for Palm in blitz.
The program was reaching ply depth 3 and missed a fork (or something like that)
at the second ply.
I'm not sure you could catch the PC version as easily, even at bullet time
controls. :)
Christophe
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