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

Author: Anthony Cozzie

Date: 17:06:17 01/14/04

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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.
>
>Uri


This is all part of Tord's secret plan to take over the world.  The real reason
Gothmog is slow is that the first line in his Search() function is:

for(i = 0; i < 1000000; i++) ;

He plans to lull us into a false sense of security and then surprise everyone at
 Tel Aviv.

Either that or he's been spending too much time around Matthias . . .

anthony



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