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Subject: Re: MTD(f)

Author: Vincent Diepeveen

Date: 15:56:08 06/17/05

Go up one level in this thread


On June 16, 2005 at 18:42:44, Vasik Rajlich wrote:

>On June 16, 2005 at 13:31:39, Vincent Diepeveen wrote:
>
>>On June 16, 2005 at 05:22:26, Vasik Rajlich wrote:
>>
>>>On June 15, 2005 at 22:40:22, Tor Alexander Lattimore wrote:
>>>
>>>>Hi
>>>>Is it possible to use a single variable in the MTD(f) search? Something like
>>>>this:
>>>>
>>>>int MTD(int depth, int guess)
>>>>{
>>>> if (depth<1) return Evaluate();
>>>> MOVE move_to_search;
>>>> int best=-INFINITY;
>>>> GenMoves();
>>>> while (GetNextMove(&move_to_search))
>>>> {
>>>>  PlayMove(move_to_search);
>>>>  val = -MTD(depth - 1, -guess + 1);
>>>>  UnPlayMove(move_to_search);
>>>>  if (val>best)
>>>>  {
>>>>   best=val;
>>>>   if (val>=guess)
>>>
>>>You missed a line here. Fail-hard is "return guess", fail-soft is "return val".
>>>
>>>Fail soft helps when you need to re-search, so it helps more in MTD (f) than
>>>PVS, and doesn't matter at all in pure alpha-beta.
>>          ^^^^^^^
>>I guess you meant a small typo here. doesn't ==> does
>>
>
>Actually I just forgot about hash effects at the next iteration. Without those,
>the statement would be true .. (as far as I can see)

The hashtable is the thing that is refuting so so many algorithms... ...one of
them is for example no-progress pruning. With a hashtable it is an incorrect way
to search.

>Vas
>
>>>
>>>Vas
>>>
>>>>  }
>>>> }
>>>> return (best);
>>>>}
>>>>
>>>>perhaps there is something very wrong with this? or perhaps it's used already, I
>>>>just noticed that on Aske Plaat's site he always uses an Alpha-Beta search with
>>>>0 width windowed searches, but doesn't this do the same thing? Is using
>>>>fail-soft type algorithms used in MTD(f) since it could well help zoom into the
>>>>correct score sooner?
>>>>
>>>>Cheers
>>>>Tor



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