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Subject: Re: About False Fail Highs, professionals, and MTD searches

Author: Josť Carlos

Date: 01:19:27 04/13/02

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On April 12, 2002 at 18:27:37, Gian-Carlo Pascutto wrote:

>On April 12, 2002 at 18:10:30, Josť Carlos wrote:
>
>>>That can't be it. If a move would be, say, only 0.03 better,
>>>you'd fail low and have to do another research to figure out
>>>if the move is a real fail high or not. Moreover, the moves
>>>that fail high the first time always end up being the PV.
>>>Essentially, Fritz has no false fail highs. I'm clueless as
>>>to what's happening here.
>>
>>  I'm not sure what you mean in this last paragraph,
>
>What it boils down to is that no matter what you have to
>open up the window to get a variation back and to be sure
>the fail-high is 'true'.
>
>>but the behaviour you
>>mention seems logical to me. I'll tell you what I do: when I fail high in a null
>>window search, I don't print anything yet. I open the window a bit (in my case,
>>half the aspiration size), and research with Alpha,Beta+AS/2.
>
>I do the same, though I just use alpha,beta.

  I made a typo, I meant Alpha,Alpha+AS/2 (AS = aspiration size).

>> I have two search
>>routines, one with high prunning level and one "careful search". I use the
>>latter here. If the search returns something above alpha, I know the fail high
>>is good, and print a fail high (with a 1 move pv).
>
>This, I don't understand. If you do the research with alpha,beta+x, and
>get something back that's below beta+x, the move is already confirmed good and
>you should have a PV to go with it, so why only the 1 move pv?

  Yes, my idea is only to confirm the fail high. Due to unstabilities of the
search, I've decided I need a "confirmation" step, to make that move th pv move
and play it if I run out of time.
  The confirmation research uses a very small window, though I still belive I'll
try smaller windows. The nature of the prunning methods we use, make search more
unstable the narrower the window is, so made the choice of trusting this
research as a true fail high, but not trusting if the returned val is inside or
outside the window. I just say "ok, now that I'm sure it must be above alpha,
I'll open the window".
  Maybe a wrong decision, but gives me stability. However, what you say makes
perfect sense and I'll try it as soon as I have some free time.
  I guess Fritz could be using a so small confirmation window that val never
falls inside it, and thus you allways see a 1 move pv. I don't know.

  Josť C.



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