Play chess against the computer and learn opening moves
Arasan v22.1
14 Sep 2020
Arasan v21.4.0.1
23 Jul 2019
Arasan v20.1.0.1
29 Apr 2017
Editorial review
Arasan v18.3.0.1
3 Feb 2016
Arasan v18.0.0.1
2 Aug 2015
Arasan v17.5.0.1
27 Jan 2015
Arasan v17.4.0.1
9 Oct 2014
Arasan v17.3.0.1
4 Sep 2014
Arasan v17.2.0.1
30 May 2014
Arasan v17.0.0.1
28 Mar 2014
Arasan v16.3.0.1
7 Dec 2013
Arasan v15.2.0.1
26 Feb 2013
Editorial review
Arasan v15.1.0.1
6 Dec 2012
Arasan v15.0.0.1
21 Sep 2012
Arasan v14.2.2.1b β
29 Jun 2012
Editorial review
Arasan v14.1.0.1
17 Mar 2012
Arasan v13.4.0.1
8 Dec 2011
Arasan v13.3.0.1
18 Nov 2011
Arasan v13.1.0.1
24 Aug 2011
Arasan v12.3.0.1
2 Feb 2011
Arasan v12.2.0.1
12 Nov 2010
Arasan v12.1.0.1
17 Aug 2010
Arasan v11.7.0.1
11 Feb 2010
Arasan v11.6.0.1
18 Nov 2009
Arasan v11.5.0.1
6 Sep 2009
Arasan v11.4.0.1
24 Jun 2009
Arasan v11.3.0.1
31 Mar 2009
Arasan v11.2.0.1
24 Dec 2008
Editorial review
Arasan v11.1.0.1
6 Dec 2008
Arasan v10.4.0.1
2 Aug 2008
Arasan v10.3.0.1
2 Apr 2008
Arasan v10.2.0.1
4 Aug 2008
Arasan v10.1.0.1
3 Sep 2008
Arasan v10.0.0.1
25 Jul 2008
Arasan v9.50.0
31 Jul 2008
Arasan v8.40.0
12 Mar 2008
Arasan v5.4
26 Jul 2008

What's new

v22.1 [6 Aug 2020]
- Remove potential passer scoring.
- Tighten validation of hash/killer moves.
- Fix Resign threshold option (CECP mode).
- Simplify lmp threshold computation. No longer different for PV.
- Modify formula for lmp count. Do not allow 0 as depth index.
- Increase razor margin and reduce razoring depth.
- Fixes to singular search code. Verify hash move before doing a singular search.
- If singular extension is triggered, do not compute any additional extension, or reduction.
- Implement bench command. Use bench command for PGO.
- Update test tools to use pentanomial model for SPRT.
- MultiPV bug fixes, including a fix for bad ponder move output in MultiPV mode.
- Fix accept draw logic (CECP mode).
- Do not update history on fail high of 1st quiet and low depth (idea from Ethereal).
- Fix possible crash: when iterating through the search threads,ensure any that have.
- a null "work" pointer are skipped.
- Allow ProbCut while in check, and restrict recursive Probcut.
- Optimization in seeSign() function.
- Misc. code cleanup.

v18.0.0.1 [2 Aug 2015]
May include unspecified updates, enhancements, or bug fixes.

v14.2.2.1 [29 Jun 2012]
Changes in Arasan14.2b (June 2012):
- Another fix for "ping" handing in engine to cure hang problems in Arasan
- Strength reduction operates during pondering.
- The chess engine handled input from the the UI in several places
and had duplicate code for scanning input and breaking it into lines.
This is now centralized and simplifed.
- Some other code cleanup, especially conversion from C-style string
handling to C++.
- Simplified code for lazy eval. Partial (lazy) scores are no longer
cached in the scoring module (such scores were seldom used anyway).
- Outpost scores reduced.
- Tweaked threshold values for history pruning and late move pruning (due
to a bug, 14.1 actually did only late move pruning above depth = 1 ply).
- Reduced thresholds for static null pruning.
- Some changes to LMR and root move reduction logic.
- Bug fix: ensure final stage of ply 0 search window widening sets a
correct upper/lower bound.
- Improvement to logic for searching checks in q-search.
- Fix material eval adjustment for Q vs 2R.
- Support is added for varying the engine strength via UCI or Winboard
options (Arasan GUI supports this too).
- GUI bug fix: search could hang when a "Go" command is issued when it
is the user's turn to move, and the user then makes a manual move before
the search completes.
- Winboard driver fixes: pings could be processed out of order in some
cases. Also, an extra move could be sent after Winboard has send a
"resign" or "result" command.

v13.3.0.1 [18 Nov 2011]
Changes in Arasan 13.3:
1) In Winboard mode, Arasan still accepts but does not rely on the
deprected "white" and "black" commands to keep track of the
computer's side of the game.
2) Winboard "level" command accepts time of form mm:ss and allows decimal
3) More general code for trapped bishop.
4) Static null pruning is implemented.
5) Dynamic null reduction based on score (aka "smooth scaling").
6) Changes to razor & futility margins and related code.
7) Fixes to history pruning. History table is global now, not per-thread.

Read more

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