Arasan 20.3

[jdart]

Arasan 20.3 is available from https://www.arasanchess.org.

Changes in Arasan 20.3:

1) Change queen mobility scoring: square reach beyond 23 squares gets
same score.
2) Re-work scoring for material imbalance with pawns.
3) Bug fixes for EPD/FEN handling (mostly affects utility programs).
4) Bug fixes for bitbases. Mate scores from bitbases were not being
transmitted to the search. Also bitbase scores were being added to
other eval terms which are not relevant for KPK.
5) Syzygy code (Fathom) is imported as a git submodule now.
6) Code restructuring, move piece values into Param class.
7) Change eval scale so Pawn value = 128 (vs. 1000 in 20.2).
8) Implement UCI "searchmoves" option to "go" command.
9) Bug fixes in parameter tuner.
10) If special-case endgame detected, skip other endgame scoring and
just use the special-case code.
11) In UCI MultiPV mode, ensure bestmove that is eventually sent is the
highest-scoring move, and re-order PVs if necessary so that they are
in decreasing score order.
12) Implement BMI2 (PEXT/PDEP) attack computation.
13) Change evasion pruning in qsearch.
14) Pack hash entries into 2 64-bits words instead of 3.

This is close to, but not identical with, the version that is playing in TCEC 10.

In my testing it is measurably stronger than 20.2, but not by a whole lot.

--Jon

[Graham Banks]

Hi Jon,

good to see further progress.

Graham.

[MikeB]

Arasan 20.3 is available from https://www.arasanchess.org.

Changes in Arasan 20.3:

1) Change queen mobility scoring: square reach beyond 23 squares gets
same score.
2) Re-work scoring for material imbalance with pawns.
3) Bug fixes for EPD/FEN handling (mostly affects utility programs).
4) Bug fixes for bitbases. Mate scores from bitbases were not being
transmitted to the search. Also bitbase scores were being added to
other eval terms which are not relevant for KPK.
5) Syzygy code (Fathom) is imported as a git submodule now.
6) Code restructuring, move piece values into Param class.
7) Change eval scale so Pawn value = 128 (vs. 1000 in 20.2).
8) Implement UCI "searchmoves" option to "go" command.
9) Bug fixes in parameter tuner.
10) If special-case endgame detected, skip other endgame scoring and
just use the special-case code.
11) In UCI MultiPV mode, ensure bestmove that is eventually sent is the
highest-scoring move, and re-order PVs if necessary so that they are
in decreasing score order.
12) Implement BMI2 (PEXT/PDEP) attack computation.
13) Change evasion pruning in qsearch.
14) Pack hash entries into 2 64-bits words instead of 3.

This is close to, but not identical with, the version that is playing in TCEC 10.

In my testing it is measurably stronger than 20.2, but not by a whole lot.

--Jon

Thanks once again Jon!

[Hugo]

At the times, when Windows 95 came out, I started with computers, and verry quick I also startetd with chess engines, chess programms.
One of the first free chess engines I saw was Arasan. It had its own interface, ready to play. I liked IT !
I am impressed that it is still under developement. Evertime I hear from Arasan updates, I remember the times of Win95 and the many nights I spent with reinstalling OS

Clemens Keck

Arasan 20.3 is available from https://www.arasanchess.org.

Changes in Arasan 20.3:

1) Change queen mobility scoring: square reach beyond 23 squares gets
same score.
2) Re-work scoring for material imbalance with pawns.
3) Bug fixes for EPD/FEN handling (mostly affects utility programs).
4) Bug fixes for bitbases. Mate scores from bitbases were not being
transmitted to the search. Also bitbase scores were being added to
other eval terms which are not relevant for KPK.
5) Syzygy code (Fathom) is imported as a git submodule now.
6) Code restructuring, move piece values into Param class.
7) Change eval scale so Pawn value = 128 (vs. 1000 in 20.2).
8) Implement UCI "searchmoves" option to "go" command.
9) Bug fixes in parameter tuner.
10) If special-case endgame detected, skip other endgame scoring and
just use the special-case code.
11) In UCI MultiPV mode, ensure bestmove that is eventually sent is the
highest-scoring move, and re-order PVs if necessary so that they are
in decreasing score order.
12) Implement BMI2 (PEXT/PDEP) attack computation.
13) Change evasion pruning in qsearch.
14) Pack hash entries into 2 64-bits words instead of 3.

This is close to, but not identical with, the version that is playing in TCEC 10.

In my testing it is measurably stronger than 20.2, but not by a whole lot.

--Jon

[Dariusz]

Thank You Jon for this amazing engine.

I will testing it today on my mac )

[Damir]

Thanks Jon for continous improvement of your engine. Do you have any estimation how much this version is stronger than 10.2 version ?

[jdart]

estimation how much this version is stronger than 10.2 version

I guess you mean 20.2. I would guess +10 ELO or so on an arbitrary rating scale where 20.2 is about 2400 ELO. So a bit more on the CCRL or CEGT scale, probably.

Also note: I don't really put any effort into optimizing or testing the MacOS version. All I do is build it and do a little sanity checking.

--Jon

[Damir]

Yes I meant 20.2 version. Sorry was a mistake on my part.

[Dann Corbit]

It's always a good day when there is a new Arasan.

[Guenther]

Arasan 20.3 is available from https://www.arasanchess.org.

Changes in Arasan 20.3:

1) Change queen mobility scoring: square reach beyond 23 squares gets
same score.
2) Re-work scoring for material imbalance with pawns.
3) Bug fixes for EPD/FEN handling (mostly affects utility programs).
4) Bug fixes for bitbases. Mate scores from bitbases were not being
transmitted to the search. Also bitbase scores were being added to
other eval terms which are not relevant for KPK.
5) Syzygy code (Fathom) is imported as a git submodule now.
6) Code restructuring, move piece values into Param class.
7) Change eval scale so Pawn value = 128 (vs. 1000 in 20.2).
8) Implement UCI "searchmoves" option to "go" command.
9) Bug fixes in parameter tuner.
10) If special-case endgame detected, skip other endgame scoring and
just use the special-case code.
11) In UCI MultiPV mode, ensure bestmove that is eventually sent is the
highest-scoring move, and re-order PVs if necessary so that they are
in decreasing score order.
12) Implement BMI2 (PEXT/PDEP) attack computation.
13) Change evasion pruning in qsearch.
14) Pack hash entries into 2 64-bits words instead of 3.

This is close to, but not identical with, the version that is playing in TCEC 10.

In my testing it is measurably stronger than 20.2, but not by a whole lot.

--Jon

Thanks a lot Jon. It's incredible that ArasanX is still a living project after decades!