Computer Chess Club Archives




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

Author: Anthony Cozzie

Date: 13:56:20 01/14/04

Go up one level in this thread

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.  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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