Computer Chess Club Archives


Search

Terms

Messages

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

Author: Uri Blass

Date: 23:41:40 01/14/04

Go up one level in this thread


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



This page took 0.31 seconds to execute

Last modified: Thu, 07 Jul 11 08:48:38 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.