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Subject: Re: QSearch() as PVS() ?

Author: Josť Carlos

Date: 06:50:18 01/15/04

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On January 15, 2004 at 02:41:40, Uri Blass wrote:

>On January 14, 2004 at 19:48:14, Dann Corbit wrote:
>
>>On January 14, 2004 at 19:08:10, Uri Blass wrote:
>>
>>>On January 14, 2004 at 18:25:34, Tord Romstad wrote:
>>>
>>>>On January 14, 2004 at 16:56:20, Anthony Cozzie wrote:
>>>>
>>>>>On January 14, 2004 at 16:26:42, Ed Trice wrote:
>>>>>
>>>>>>
>>>>>>>
>>>>>>>Have you considered trying MTD(f) instead of PVS?  I am not sure it is any more
>>>>>>>efficient in practice, but it is easier to code, and has the additional benefit
>>>>>>>of making you feel different, original, interesting, intelligent, handsome and
>>>>>>>attractive.
>>>>>>>
>>>>>>
>>>>>>Well Aske Plaat would love to hear that :)
>>>>>>
>>>>>>But doesn't MTD(f) trigger a great deal of researches? I remember trying that
>>>>>>once and it bloated the tree.
>>>>>
>>>>>---- opinion mode on ----
>>>>>
>>>>>MTD(f) has two big problems.
>>>>>
>>>>>1, you ponder the wrong move occasionally because your PVs are less accurate.
>>>>>If you are pondering the wrong move 20% of the time that is equivalent to a 10%
>>>>>time loss.
>>>>
>>>>This is not a *big* problem by any stretch of the imagination.  It does indeed
>>>>happen
>>>>that the last few moves of the PV are wrong or missing, but I have *never* seen
>>>>as obviously wrong move as the second move of the PV.  This does of course not
>>>>mean that it never happens, but it is clearly very rare.
>>>>
>>>>On the other hand, it *does* happen that the PV contains only one move, and
>>>>there
>>>>is no move to ponder at all.  This happens maybe once every 5 or 10 games, but
>>>>usually when the game is already won or lost.
>>>>
>>>>>2, MTD(f) is at its worst when the score is dropping.  A fail high in MTD(F) is
>>>>>much faster than a fail low (1 child node vs all child nodes).
>>>>
>>>>This is true.  The average branching factor is clearly lower when the initial
>>>>direction
>>>>of the search is downward.
>>>>
>>>>>Unfortunately,
>>>>>this is when you need your search the most: you are in trouble, and you need to
>>>>>make exact moves to win/draw (you might already be lost, but thats just the way
>>>>>it goes).
>>>>
>>>>Most of us extend the thinking time in such situations, and try to avoid making
>>>>a
>>>>move before the search fails high.
>>>>
>>>>By the way, there are a few things you could try to solve the problem you
>>>>describe,
>>>>although I haven't yet tried them.  The main idea is to give up quickly if the
>>>>search
>>>>appers to fail low.  The easiest thing to do is to just abort the search if the
>>>>first move
>>>>at the root fails low, and immediately start a new search with a lower search
>>>>bound.
>>>>
>>>>It is certainly possible to find refinements to this idea, but as I said I
>>>>haven't experimented
>>>>with it yet.
>>>>
>>>>>I remember some Zappa-Gothmog games where Gothmog had been searching
>>>>>8 ply, got in a tight spot, made a 6 ply search, played a huge blunder, and went
>>>>>from -1 to -5 the next move.
>>>>
>>>>It is quite common that the search depth reached varies a lot from move to move
>>>>in Gothmog (a difference of 3 or 4 plies is not unusual), but usually this is
>>>>due to
>>>>DFP rather than MTD(f).  A sudden dramatic drop in search depth usually means
>>>>that most of the DFP is disabled for some reason.
>>>>
>>>>And in general, if you want to knock MTD(f), you really need to base your
>>>>conclusions on
>>>>something more substantial than games against Gothmog, which undeniably is the
>>>>slowest, weakest and most buggy MTD(f) engine known to man.
>>>
>>>I do not believe it.
>>>
>>>PostModernist also use MTD and I think that Gothmog is stronger than
>>>PostModernist.
>>>
>>>I did not test Gothmog and my impression is based on results that I read that
>>>suggest that Gothmog is at the same level of engines like Ktulu.
>>
>>I think you underestimate PostModernist.  It may be stronger than SOS (often
>>considered the strongest MTD(f) engine), and so it is surely one of the
>>strongest MTD(f) engines around.
>
>No
>I do not underestimate PostModernist.
>Your list suggest that it is weaker than Abrok or Anmon when the list that I
>read suggested that Gothmog is stronger than them.
>http://www.f11.parsimony.net/forum16635/messages/60395.htm
>
>I see that you test old SOS.
>I am surprised to hear that SOS is often considered to be the strongest MTD
>engine.
>
>I thought that this title is of one of the commercial(Shredder showed stupid
>pv's so it may use MTD and I also remembered that the same happened with Fritz)
>
>I do not know how did you get that PostModernist is one of the strongest MTD
>engines in the world.
>
>I do not know which engines use MTD and I simply mentioned the probably weaker
>engine out of the only 2 free engines that I knew to use MTD except
>Gothmog(PostModernist and Comet)
>
>Gothmog may be also stronger than Comet.
>
>Uri

  Comet is MTD(f)? I haven't noticed it. However, Anmon clearly is.
  BTW, Cilian looks like it is MTD(f) too, in which case it is the weakest
MTD(f) engine that I know of.

  Josť C.



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