Author: Robert Hyatt
Date: 19:45:04 01/12/06
Go up one level in this thread
On January 11, 2006 at 12:34:42, Stuart Cracraft wrote:
>On January 10, 2006 at 21:44:30, Robert Hyatt wrote:
>
>>On January 10, 2006 at 16:15:53, Stuart Cracraft wrote:
>>
>>>Hi - my extension credit is calculated for each ply in the search
>>>and stored in several arrays, one for each type of extension.
>>>
>>>The arrays for the given current ply are summed together
>>>
>>> extension=0; // Prove that we must extend. We assume we don't at first.
>>> :
>>> :
>>> AllExt[ply]=ChkExt[ply]+RecapExt[ply]+PawnExt[ply]+OneExt[ply]+ThreatExt[ply];
>>> if (AllExt[ply]>=1.00) extension=1;
>>> else if (ply>0 && AllExt[ply-1]<1.00 && AllExt[ply-1]+AllExt[ply]>=1.00) {
>>> extension=1;
>>> }
>>> else if (ply>1 && AllExt[ply-1]<1.00 && AllExt[ply-2]<1.00
>>> && AllExt[ply-2]+AllExt[ply-1]+AllExt[ply]>=1.00) {
>>> extension=1;
>>> }
>>> if (BM_X != 0.0)
>>> if (bmx) {
>>> AllExt[ply]+=BM_X; extension++; bmext++;
>>> }
>>>
>>>And if extension is "1" after all of this, then we extend by 1 the
>>>current move at the current ply known as 'ply'.
>>>
>>>My questions are:
>>>
>>> I know that Bob Hyatt has used 0.75 as his check extension for many years
>>> and indicates it is a critical factor in throttling runaway check extensions.
>>
>>Not quite. My "check" extension is 1.0. My "one-legal-reply" extension is .75,
>>as is the recapture and mate threat extensions. But normal check is 1.0 until
>>some ply limit is reached, at which point is is reduced to .5 to limit
>>ridiculously deep searches.
>>
>>
>>
>>> My problem is that since I sum as above, setting the credit for CheckExt[ply]
>>> (before the above code) to 0.75 would really be too little of a good thing,
>>> nothing in fact, since I would only extend a check if there is an additional
>>> consideration forcing a full extension and that is not what Bob meant.
>>
>>You are missing another point that is very significant. I am not doing
>>extensions like you. I simply increment "depth" by the amount of the
>>extensions, even if the total is something like .75. That won't cause a deeper
>>search yet, but if a later ply adds just .25 more, then suddenly the search will
>>go one ply deeper. It didn't appear that you are doing it that way. My
>>fractional extensions are carried along, ply by ply, and slowly build up until
>>they cause another ply of depth to be searched...
>>
>
>At which point you then reset the additive to zero so that it can start
>accumulating again?
No, it is just added to depth at each ply. And each time I advance one ply, I
subtract 1.0 from depth... For my one ply search, depth starts off at something
like 1.5 (you can look at iterate.c in crafty to see what SearchRoot() is
actually called with, I have changed this more than once). So even a .75
extension will cause the search to go to 2 plies rather than one, since 1.5 +
.75 is 2.25... and since depth is always reduced by 1.0 for each ply, and
sometimes gets incremented by as much as 1.0 in a single ply, the depth carries
the extension amount along all the way until the last call to search drops depth
below 1.0 and no extensions are done at that ply, dropping me to the q-search on
the next ply...
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