Computer Chess Club Archives




Subject: Re: Null-Move: Difference between R = 2 and R = 3 in action

Author: Sune Fischer

Date: 12:22:48 07/21/02

Go up one level in this thread

On July 21, 2002 at 14:38:38, Robert Hyatt wrote:

>On July 21, 2002 at 03:36:23, Sune Fischer wrote:
>>On July 21, 2002 at 03:29:51, Uri Blass wrote:
>>>On July 21, 2002 at 03:16:40, Sune Fischer wrote:
>>>>On July 20, 2002 at 22:22:22, Robert Hyatt wrote:
>>>>>On July 20, 2002 at 08:13:44, Gian-Carlo Pascutto wrote:
>>>>>>On July 20, 2002 at 08:04:01, Sune Fischer wrote:
>>>>>>>I think it matters "a factor of 2".
>>>>>>>1) it helps you to prune
>>>>>>>2) you get better evaluation in the upper plies when you can return a score
>>>>>>>based on a deeper search.
>>>>>>>number one will show itself directly because you iterate deeper, the second one
>>>>>>>you don't "see", but it does improve depth along some branches in the same way.
>>>>>>1) I get +- 10% hash hits (and less prunes) in typical middlegame. Not enough to
>>>>>>matter a factor of two (but I didnt check this so not 100% sure).
>>>>>>2) Uh?
>>>>>Run your program with a tiny hash and a deep search.  Then a big hash and
>>>>>a deep search.  In middlegame positions this will be at least a factor of
>>>>>2x.  Measure time to depth.  Small hash might take 4 minutes to get to depth
>>>>>12, then big hash will take around 2 minutes...
>>>>You shouldn't measure time to ply, that would not give you the full benefit of
>>>>the hash. You should use time to find the right move.
>>>>I have never seen the hash bring only a factor of 2, even in middlegame.
>>>>Last I tested I saw a mate in 5 being solved in 1/4 of the nodes with the hash.
>>>Do you use killer moves?
>>>I know that at least in version 1.17 you do not do it.
>>>Not using killer moves can increase the advantage
>>>of hash tables.
>>That is right, for some reason they increased the size of the tree.
>>I found an error in my validate move rutine, perhaps it's time to try them
>>But I still say time-to-ply is not the right way of testing, a "ply" is
>>meaningless in this regard.
>OK.. A statement I can actually live with, finally.  :)
>You are correct in the tree searched with hashing and the tree searched without
>hashing have differences.
>1.  transpositions are eliminated, making the hash tree smaller.
>2.  move ordering is better with a hash tree.
>3.  The hash tree grafts information from one branch to another, making it
>potentially more accurate, for the same ply.
>But, since there is no real way to measure anything else (ie if you measure
>time to solution for both it could still be criticized in the same way since
>the hash tree will be a bit more accurate in addition to being faster...  So
>even comparing that is flawed...

Okay, there is an easier way then:)

Take a strong program, test its strength with and without hashing.
Now we know double speed is about 40-60 elo(*), compare that to the hash

That should be far easier to measure, it would also include everything from
opening, mid to endgame making the whole discussion more realistic and less

As usual I doubt the experiment will be done, because we don't care about the
result as long as hashing == more rating!

(*) (depends on program, pool of players etc. but let's not get into that :)

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