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Subject: Re: how to back up the PV with minimal work.

Author: Sune Fischer

Date: 11:31:55 01/21/04

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>nonono...
>
>We only do it on PV nodes....
>
>I can't possibly do it if I can fail low, except for the rare cases where
>the root aspiration window alpha bound is too high and the best move is
>actually worse than the expected bound.

But you can fail-low, so that's what I don't understand.
You have the condition:

    if (ply & 1) {
      if (alpha!=root_alpha || beta!=root_beta) break;
    }
    else {
      if (alpha!=-root_beta || beta!=-root_alpha) break;
    }

Nothing in principle prevents the search from returning score<=root_alpha.

>But fail-low or fail-high at the
>root is not that common, and there I only do it when (a) I expect a hash
>move and don't have one,

But what is your condition for expecting a hash move, other than being on the
PV?

-S.



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