Computer Chess Club Archives




Subject: MTD: an observation and a question

Author: martin fierz

Date: 19:14:57 09/11/02

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

(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?


This page took 0.01 seconds to execute

Last modified: Thu, 15 Apr 21 08:11:13 -0700

Current Computer Chess Club Forums at Talkchess. This site by Sean Mintz.