# Computer Chess Club Archives

## Messages

### Subject: Re: Fail high reductions

Author: Gerd Isenberg

Date: 13:18:13 07/02/03

Go up one level in this thread

```On July 01, 2003 at 18:10:46, Martin Bauer wrote:

>On July 01, 2003 at 17:34:47, Russell Reagan wrote:
>
>>From "Fail High Reductions by Rainer Feldmann"
>>
>>"...a fail high node is a node 'v' with a search window of [alpha,beta] at which
>>a static evaluation function 'c' produces a cutoff. The FHR-algorithm reduces
>>the search depths at these fail high nodes thus searching their subtrees with
>>less effort."
>>
>>Their subtrees? I thought fail high nodes didn't have subtrees, and that you
>>return beta at a fail high node. I must be misunderstanding something. Could
>>someone give a simple explaination of how fail high reductions work?
>
>No, hope I am right:
>
>You evaluate in even at inner nodes. If your static evaluation is already better
>than beta, you expect a beta cutoff. So you reduce the remaining depth to get
>the cutoff.
>
>May be there are some extra condiotons for the reduction.
>
>Martin

Hi Martin,

yes
if ( eval - t >= beta and nullwindow ) then d = d - 1;

The threat value t is either computed staticly (inside eval, e.g. en prised and
hanging pieces, possible forks, pins, king attacks and other "tactical"
heuristics) or by nullmove (quiescence) search.

Gerd

http://www.talkchess.com/forums/1/message.html?304306

```