# Computer Chess Club Archives

## Messages

### Subject: Re: Couple of chess programming questions

Author: Andrew Williams

Date: 02:10:49 09/11/02

Go up one level in this thread

```On September 10, 2002 at 18:03:02, Gian-Carlo Pascutto wrote:

>On September 10, 2002 at 17:08:23, Dann Corbit wrote:
>
>
>>Since it searches until upperbound and lowerbound converge, evidently, they can
>>exchange roles.
>
>They do not within an MTD search. The search process goes like this:
>
>guess: 50
>
>first search: fail low at 50, new guess 49
>second search: fail low at 49, new guess 45
>[...]
>twentieth search: fail low at -20, new guess -19

You mean fail high?     ^^^

>twentyfirst search: fail high at -19
>

Admittedly I'm jumping into this discussion half-way through, but if in your
second search you drop by 4 units, how can you be sure that you'll always
straddle the score by 1? In other words, couldn't the score be -18 if  you fail
high at -20? In which case you do have an interval at one point? So you can
approach the score from two directions (if you increment/decrement by > 1).

Given this, you *can* find that you've got a gap between the upperbound and the
lowerbound. However, I've never been able to improve my scheme with a binary
chop.

Andrew

>At this point, we have converged at -19.
>
>It always goes in a single direction. This isn't a binary search
>by any definition.
>
>--
>GCP

```