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

Author: Matthias Gemuh

Date: 04:48:42 01/15/04

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On January 15, 2004 at 06:59:15, Volker Böhm wrote:

>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.
>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.
>Don´t use PVS in QSearch.
>Greetings Mangar

Thanks for this elaborate answer.
BTW, in QSearch I also generate moves for

1) all passed pawns
2) all attacked pieces moving to unattacked empty squares


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