What does "Arasan" mean?

Arasan means "king" in Tamil, a language spoken in South India and Sri Lanka. It is related to the Sanskrit word "raja." The Arasan website header has "Arasan" written in Tamil script.

How strong a chess player is Arasan?

It is hard to answer that because Arasan does not play against humans in rated tournaments. So without that, you can't assign it an exact rating comparable with human ratings.

Some independent testers run matches with Arasan and other programs and assign ratings (see especially CEGT and CCRL), but the numbers are pretty arbitrary. They tell you one program is stronger than another, but the absolute values are going to be different across the rating lists, and probably different from human ratings.

I think Arasan made an illegal move. I moved my pawn two squares forward and Arasan captured it with the pawn next to it.

This is called an "en passant" capture (French for "in passing"). It is a legal chess move. See this Wikipedia article for a detailed explanation of the en passant rule.

How can I configure Arasan for best performance?

You should set the "threads" option to the number of physical cores on your computer, and you should set the hash table size reasonably large but probably not more than 1/2 of the RAM on your computer. (Arasan also runs somewhat better on a 64-bit operating system).

If you are using a user interface such as the native Arasan GUI you can set the threads and hash options using the interface (see the Options menu).

UCI compatible UIs like Fritz or Shredder also support setting these options. If using Winboard, see the readme.txt file.

Arasan is too strong for me! Can I make it play weaker so I can beat it?

Arasan versions 14.2 and higher support a strength limitation option. If using the native Windows GUI, choose the Options menu and bring up the Preferences dialog to set the relative playing strength. The range is 0-100 (0 is minimum strength, 100 is maximum). 100 is very challenging; 0 is quite weak, although it will still exploit any really bad mistakes you make such as leaving pieces hanging.

When I try to run arasan.exe, the Arasan window is not active, but the bottom tool bar shows Arasan is running. Clicking on it does not show the application.

I have occasionally had reports of this problem. You can try this:

1. Run the program "regedt32" (from the Start Menu, click Run and then type in this name).
2. Regedt32 shows a list of folders on the left-hand side. Click on the + button next to "HKEY_CURRENT_USER" to expand it.
3. Click on the + button next to "Software"
4. Select the "Arasan" folder. Type the delete key. It will warn you about deleting but just say Yes - it is safe.
5. Restart Arasan.

This removes any settings in the Registry and will cause Arasan to start with default values, including board size and location.

I want to distribute Arasan on a CDROM or in a magazine or though download.

The Arasan chess GUI and chess engine binaries on this site are freely redistributable, provided that:

1. They are distributed in unmodified form.
2. No more than a nominal fee is charged for copying or media.

If you think your distribution arrangement isn't covered under this, or need some more formal authorization, please contact me.

I want to use Arasan in a commercial product or Web offering, possibly in a modified version.

Arasan chess engine source code is available under the MIT license (see license), which permits reuse in this way.