Author: Albert Silver
Date: 07:29:18 07/22/99
Go up one level in this thread
On July 21, 1999 at 06:41:25, Ed Schröder wrote:
>>I took a look at the log file you placed on your site so as to show what would
>>be subject to tweaking and found that what interested me most was all grouped
>>up. I am thinking particularly of Chess Knowledge which is said to increase or
>>decrease the quality of positional play according to its value. This is quite
>>vague, and I would have thought that it was precisely in the various
>>elements of
>>chess knowledge that one could achieve the most interesting tweaking. Is this
>>left like this due to a desire to not divulge all of Rebel's cogs and screws?
>>
>> Albert Silver
>
>The option [Chess Knowledge] is about LAZY-EVAL which is currently
>a hot topic here. Below is a quote from my pages which might explain
>a bit (I hope).
>
>Ed Schroder
>
>-----------------------------------
>
>[Chess Knowledge = 200] Chess Knowledge above 100 will result in
>more accurate positional play but a lower search depth. Chess Knowledge
>below 100 will result in less accurate positional play but a higher search
>depth. This function needs a detailed (and quite technical) explanation:
>
>The heart of a (any) chess program is its evaluation function (EVAL). In
>there all chess knowledge is present. The most important ones are already
>discussed above (King Safety, Mobility, Pawn Structure, Passed Pawns
>etc). Above these major items EVAL contains over 200 specific (position
>oriented) chess knowledge cases of all kind. To name a few: Bishop of
>opposite colors, bad (or good) bishops, piece development in the
>opening, castling, rook endings, pawn endings and and and... EVAL is
>the soul of a (any) chess program and will reflect the playing style the
>programmer has (had) in mind.
>
>EVAL in REBEL takes a lot of processor time even for todays fast
>computers. EVAL's size is over 120 Kb (pure assembler code)
>containing over 30,000 instructions which is very big for a chess
>program. Calling EVAL for every position in the tree-search is very
>expensive and will slow down the search tremendously, in REBEL's
>case a slow down factor of 7 to 8 (nodes per second) is not unusual.
>
>To handle this chess programmers invented LAZY EVAL in all kind
>of sorts. LAZY-EVAL is a smart algorithm that only picks the main
>important parts of EVAL belonging to the (current position) and then
>skips the rest of EVAL. This is of course a very dangerous approach
>as often LAZY-EVAL is not 100% right and will return a score that isn't
>100% accurate which (sometimes) in the end may result in a lesser
>quality move.
>
>On the other hand Rebel's LAZY-EVAL algorithm will speed-up the
>search tremendously and allows REBEL to look 2-3 plies deeper
>than without LAZY-EVAL which in the end is by far is superior in
>terms of chess strength.
>
>With the option [Chess Knowledge = 200] you can tune REBEL's
>LAZY-EVAL. The higher you set its value the more accurate REBEL
>will play but the search depth will decrease. If you set Chess
>Knowledge to its maximum [Chess Knowledge = 500] you actually
>see REBEL's EVAL in its full glory as LAZY-EVAL is hardly active
>anymore.
>
>However REBEL'S nodes per second (NPS) will drop typically with
>a factor of 7-8. On a PII-333 REBEL searches about 100,000
>positions a second. Using [Chess Knowledge = 500] REBEL's
>NPS will drop to 12,000-15,000.
>
>More technical stuff: all of the above is true for current and older
>INTEL processors. However times are changing, chips are equiped
>with larger and faster cache memory. On the new AMD-K6-III the
>cache runs at full processor clock speed. INTEL processors cache
>memory is just running on 100 or 66 Mhz. The result is that on
>AMD K6-III using the maximum [Chess Knowledge = 500] REBEL
>will run 2-2½ times faster than on INTEL.
>
>All of this makes it very difficult to tune Chess Knowledge for its
>best setting because it is very dependant on the processor you
>have in your PC. This month AMD released the new K7 processor
>which again doubled the cache memory and REBEL will profit a lot
>from that. INTEL surely will answer. The bottom line is that one day
>the ideal setting will be [Chess Knowledge = 500] and you can use
>REBEL's EVAL in its full glory.
How much of Rebel's EVAL will users be able to modify? I presume that most of
the specific knowledge will not be accessible, but some will. What?
Albert Silver
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