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Subject: Re: QSearch() as PVS() ?

Author: Volker Böhm

Date: 03:59:15 01/15/04

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On January 14, 2004 at 15:44:56, Matthias Gemuh wrote:

>
>
>Does it make sense to use PVS algorithm to implement QSearch ?
>It does not seem to help my engine.
>
>/Matthias.

PVS is good if

1. there are many alternative nodes (never got good results in my connect-4 game
with 7 moves max. at one ply)
2. the move ordering is good
3. you can narrow the window greatly compared with the usually arising
position-values in a search.

In QSearch:

1. Depends a little bit what nodes you are searching. If you only search "good"
hits selected by SEE its verry narrow. If you are searching check-moves too it´s
wider. You can consider PVS if searching check-moves tool.
2. Move ordering in QSearch is seldom good. You haven´t got a PV and seldom
usefull hash-moves. If you turn off SEE for "good hit-moves" the ordering is too
bad for PVS
3. I´am staring a new search with a windows of -30cp .. +30cp around the search
result of iteration-1. The window in QSearch is often of witdh 0, but verry
seldom of width > 60cp (only if I´ve got fail-high or fail-low against the
initial window). The results of a QSearch differ greatly as they are hitting
material. The least effective hit move gets +100cp. Conclusion: the window is
allready verry narrow compared to the results of QSearch calls.

Conclusion:
Don´t use PVS in QSearch.

Greetings Mangar





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