Author: Stuart Cracraft
Date: 08:02:37 08/08/04
Go up one level in this thread
On August 07, 2004 at 19:32:14, Peter McKenzie wrote:
>On August 07, 2004 at 17:06:30, Stuart Cracraft wrote:
>
><snip>
>
>Your code still looks buggy to me, but that may in part be because it is a
>mixture of real and pseudo code?! Comments below:
>
>>
>>Okay I changed to:
>>
>>int quiesce(alpha,beta)
>>{
>> if (repetitioncount()==2 || 50moverule()) return(0); // draw
>> if (incheck()) return(mainsearch(depth=1,alpha,beta)); // check extension
>
>This usage of incheck() implies that the incheck function determines if the side
>to move is in check. The usage later on is inconsistent with this.
incheck() says is the side to move in check, i.e. for extension, avoidance
of null move, etc.
the second incheck, which was a typo and should have been incheckopp()
after the makemove loop is for when the side that just moved and to
see if it is incheck (i.e. illegal move)
sorry for the confusion on the quick pseudocode.
>
>> base = value = eval(); // evaluate
>> if (value >= beta) return beta; // cutoff
>> if (value > alpha) alpha = value // establish value
>> generate capture moves; // get all captures, just captures
>> while another capture move available
>> {
>> value = base + see(destination_square_of_this_capture);
>
>Does your see function take pc-sq value of the captured piece into account? If
>not, then you should probably include an error margin term into value. So the
>above line would become:
yes -- eval() returns simply the material affeced by pc/sq.
> value = base + see(destination_square_of_this_capture) + margin;
>
>> if (value > alpha) {
>> if (value > beta) value = beta;
>> makemv();
>> if (!incheck()) value = -quiesce(...,-value,-alpha);
>
>Here the usage of incheck implies that the incheck function determines if the
>side *not* to move is in check. That is inconsistent with the previous usage
>and would appear to be a bug. This deduction is based on the assumption that
>makemv() changes the side to move, is that correct?
Please see above.
>
>Also, what exactly does the '...' mean in your call to quiesce?
Mostly bookkeeping and statistics. I probably could save a small amount
of time doing it globally instead of on the stack.
>
>Another thing that looks odd is the way you are changing beta. Why not just call
>quiesce with -beta, -alpha? After all, its still an alpha/beta search.
This was Alessandro's suggestion. Please see him. There is another thread
on SEE where he explains it.
>
>It seems to me that if SEE predicts that the capture will exceed alpha but not
>beta then you take this as gospel and adjust beta downwards accordingly. That
>seems plain wrong as it will hide mistakes of SEE that would otherwise be found.
> For example SEE may think you are winning the exchange but in reality you are
>winning a rook because the defender is pinned.
>
>
>> else value = MINNUM
>> unmakemv();
>> }
>> if (value >= beta) return beta;
>> if (value > alpha) alpha = value;
>> }
>> return(alpha);
>>}
>>
>>Also I discovered a bug in SEE that wouldn't find a pawn attacker
>>of the given see(sq)'s sq target for the exchange if the pawn
>>attacking was black.
>>
>>That is fixed and the SEE is verified for both sides in exchanges
>>of different types for white and black and saw no problem.
>>
>>Still, with the above two fixes, the SEE() is doing worse. (Fewer
>>nodes searched and less problems solved.)
>
>Fewer nodes searched is better, right? For a fixed depth, SEE will always solve
>fewer (or the same number of) problems than non-SEE. It is just another form of
>pruning after all!
>
>>
>>I put in some code to show me the moves being rejected (see(bd,sq)<0)
>>along with a board printout for each and all the moves shown were
>>losing exchanges so I am confident it is working.
>>
>>I still think it is due to my use of material-only/pc-sq and
>>an attack-finding routine, in support of see, that is as slow
>>as doing a makemv().
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