Computer Chess Club Archives




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

Author: Filip Tvrzsky

Date: 14:20:46 01/14/04

Go up one level in this thread

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
>>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.
>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).  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).  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.
>---- opinion mode off ----
>Most people that try MTD(f) will give up very fast because it requires a
>two-limit hash table rather than a bound hash like most people implement.

I have noticed this in several postings before but still do not follow: why is
with MTD(f) necessary to store two limits in hash table instead of only one?

>Its a
>difference of style, but in my opinion worst case performance is key when for
>search.  There is some interesting room for work IMHO with MTD(f)/PVS hybrids.

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