Author: Stuart Cracraft
Date: 13:15:53 01/10/06
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.
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.
Beyond the above extensions,
Check
Recapture
Pawn on 7th rank
One move only in position
Mate Threat (e.g. value of null move is showing mate in a couple ply)
Botvinnik-Markoff
Carry-Over Extension (e.g. neither of the last two ply generated an
extension but their sum does, then extend)
-- also same for last 3 ply.
is there an important extension or method that is necessary and beneficial?
I currently have all of the above extensions being 1 full ply, except mate
threat and pawn on 7th are 0.5 (half a ply).
I know there are many bugs in this such as why am I doing [ply] and [ply-1]
and [ply-2] when the program's moves are [ply] [ply-2] and [ply-4] which
I just saw while writing this message.
I believe my extensions, being what they are, is why I can get only a
half-decent result on my tests, and that a better-debugged extension
implementation will reap fruit (no - not THAT kind of fruit!)
Stuart
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