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Subject: Re: MTD: an observation and a question

Author: Vincent Diepeveen

Date: 05:16:09 09/13/02

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On September 11, 2002 at 22:14:57, martin fierz wrote:

>prompted by the discussion on MTD before, i decided to look once again what my
>program does.
>
>1. observation
>dann corbit suggested that MTD works "binary-search-like" in zooming in on the
>true value, in the sense that it converges rapidly. assuming the grain size of
>my eval to be 1, i have seen ONLY search window changes of 1. like when my eval
>jumps from 0 to 10

Fail soft or fail hard is not the issue here.

It depends upon the program. Very general speaking, the more minimal
the tree is, the more likely it is that you get back value + 1 in case
of a fail high, or value-1 in case of a fail low.

>(0,1) returns value 1
>(1,2) returns value 2
>...
>(9,10) returns 10
>(10,11) returns 10.
>
>not once did i see it do something like
>(0,1) returns value 9
>
>i forget which is which, fail-soft/fail-hard, but i'm using the one which
>returns the maximum of the successors, not the one which returns beta. so in
>theory (0,1) could return 9, but it never does. i guess that's not really
>surprising, since alpha-beta just tries to do as little work as possible :-)

>2. question
>my question is related to bob's "bouncing over". MTD necessarily has to bounce
>over once, as in the example above, it has to search both (9,10) and (10,11),
>and fail high on the first search, and fail low on the second. so the question
>is: isn't this bouncing over too? and if this is really bad, then: has anybody
>ever measured the difference between MTD storing just one bound in the hashtable
>with storing both bounds?

Yes i remember an extensive discussion about this, but afraid to speak
about something which could have been in an email discussion instead of
a public discussion, i will shut up about it.

My personal experiment it was 2 bits: fail high, fail low, true bound.

>cheers
>  martin



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