Author: guy haworth
Date: 09:57:30 01/28/01
Go up one level in this thread
Eugene's EGTs are best in real-time because:
1) they cover wtm and btm
2) physical file-compression and front-end caching have been used
3) the indexes are more compact because 'unblockable checks' are avoided
See ICGA_J v23.3 last year. I don't believe that significant improvements can
be made just by taking these ideas further. There are ideas for reducing the
index-size of (e.g.) KQR... and KQP.... EGTs but they only save a few %.
It would seem better to preface the Nalimov/Thompson EGTs with a values-only
EGT, two bits per position (1-0, draw, 0-1 and 'broken') so that it is not
necessary to go to the disc to find out the 'depth' of moves that reduce the
theoretical value of the position.
Peter Karrer has revisited ideas first demonstrated by Thompson (KQPKQ, KRPKR)
and Schaeffer (checkers) whereby positions with the same P-positions form a
contiguous sub-EGT of the EGT. Thompson also separated positions with different
patterns of Bishop-square-colours.
The best way to get compression would seem to be to preface the EGTs of 'ground
data' with some higher-level rules, avoiding the need to keep data about
positions that can be dealt with by the rules.
A trivial example would seem to be:
"In KQQQQK, sacrifice Queens until it is KQK provided that ...."
[What point is there in computing this EGT?]
Christoph Wirth and Ernst Heinz have both, independently, done some work on
pragmatic rules that may not play optimally and may not even win every
half-point ... but DO shrink the EGT-size bigtime.
By surveying databases of games, you can see which endgames are most likely to
come up. Some 6-man pawnless 3-3 endgames have never featured on these
databases.
G
The set of available EGTs can be slightly improved by using other metrics than
DTM. Minimaxing DTC instead of DTM, DTZ instead of DTC (and sometimes, oddly,
DTC instead of DTZ, and DTM instead of DTC) can avoid a 50-move draw.
See some examples of mine in ICGA v23.2 last year.
The guaranteed way to avoid a 50-m draw-claim is to use (what I call) the DTR
metric ... 'Distance by The Rule' ... which minimises the length of the longest
phase in the subsequent game. It is used in conjunction with the DTZ table.
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