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

Author: Volker Böhm

Date: 06:56:26 01/15/04

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On January 15, 2004 at 08:06:34, Tord Romstad wrote:
>I generate safe moves for hanging pieces if all of the following are
>satisfied:
>
>a) The value of the static eval is >= alpha.
>
>b) At least two of the pieces for the side to move is hanging.
>
>c) static_eval-(value of capturing the smallest hanging piece)/4 < alpha>
>d) I am in one of the first two plies of the qsearch.
>
>Always generating all safe moves for all hanging pieces is probably a
>waste of time.  For instance, if you are a queen up, it is not very
>important to find out whether it is possible to save a hanging knight.
>And in positions with only one hanging piece, it will usually be safe
>to assume that the piece can be saved.  Of course there are exceptions,
>but I think it is better to ignore them and use the time saved to
>search deeper.

Hanging pieces in the qSearch?! I planned (not yet implemented) to search one
ply deeper if my eval reports:

1. More than one hanging pieces (and pieces attacked by less valuable pieces).
2. A tied (hope this word is correct, I mean a piece that can´t move because it
has a king or a valuable or hanging piece behind) piece attacked by a "smaller"
piece.
3. Some kind of mate threads

Tried this too?

How did you implement the "hanging piece" move? In q-Search you are never forced
to move. That´s why the resulting value is max(current-static-value,
qSearch-value). Moving away hanging pieces wouldn´t give much additional value.
Conclusion: This results to nothing. Only possibility is to give hanging pieces
a huge negative score in eval. Drawback: a hanging piece that is easily defendet
by another piece gets a negative score but is quite ok.

Thats why I tend to extend the search by one ply if these situations arises at
the horizont.

Greetings Mangar.



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