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Subject: Re: Time control legend

Author: Don Dailey

Date: 07:27:28 05/16/98

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>>>>I dunno why Rebel+Fritz+genius and some others
>>>>are so horrible in these exchanges, but my first guess was piece square
>>>>tables. Now i say: perhaps mobility is a reason too.
>>>>The common thing of all these programs compared to Crafty, Zarkov, Diep
>>>>and some others is that they lack mobility terms.

I know this is not correct for Genius.  One of the few things Richard
Lang ever "gave up" about his program was some details on the mobility.
He even does queen mobility.   Of course this was a few years back,
it's possible he stopped using mobility.

I am curious about different implementations of mobility.  Here is a
quick
rundown of ways I've done BISHOP mobility through the years:

1) Simple square count method (legal moves)
2) Simple square count where I pretend only pawns on board.
3) Combinations of 1 and 2 folded together.
4) Method 2 with table.
5) Method 1 or 2 but pawn attacked sqaures count less or not at all.
6) Not at all.

Method 4 is something I found useful.  I count the squares but use the
count to index a table.  The table is designed to emphasize "minimal
mobility",  I consider it more important to go from zero to 5 sqaures
that to go from 5 to 10.  This helps a lot in positions where you choose
to "improve" a well developed bishop when you should be doing more
constructive things.  I don't have proof this is any better, it's a seat
of the pants thing from observing lot's of games.

I think method 5 is the very best, but my programs found it quite
expensive to compute, others might do better.  I may eventually
implement this in Cilkchess because with bit boards it will probably
be fairly cheap.

Method 3 seems like an improvement over either 1 or 2, but I believe
method 1 is the least good.  But in some positions it makes more sense.
Nothing is completely ideal for every situation.  So I generally give
more weight to pawn considerations.  I also had a program that didn't
count squares where pieces blocked it but skipped over them until it
ran into a pawn.

As far as rook mobility is concerned, I believe it's more important
to judge open and half open files.  I think rank mobility is useful
if the weight is kept low, the same probably applied to file mobility
but again, prime consideration is openness.   One consideration is
attacking enemy pawns.  Is it mobility restricting, or is it a good
thing?  The answer is both!  I try to focus on what I'm measuring,
and I'm not measuring rook bonuses for attacking pawns.  Since I'm
measuring mobility, I oount pawns that can be captured as mobile
squares but don't count any farther.  I have a separate term for
various attacks on undefended pawns.

Method 6, I don't know about.  Right now cilkchess using this method
and I feel like I have problems too often with bishops. I have some
static" terms that judge a bishop's worth like pawn counts on certain
color squares and a term that attempts to measure a bad bishops
which I have mixed feelings about.   Also a table with weak weights
to get the bishops out to the center a little.  Sometimes though,
the bishops get confused about where they belong.

- Don



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