13. UCI Engines

Sigma Chess 6.1 supports the free open UCI (Universal Chess Interface) protocol. This means that you can use third party chess engines such as the world class HIARCS UCI engine instead of the built-in Sigma Chess 6.1 engine. Note: UCI support is only available under Mac OS X.

The UCI protocol was introduced by Stefan Meyer-Kahlen (author of the top PC chess program Shredder) as an alternative to the Winboard protocol. There are many UCI engines available for Windows and some have also been ported to Mac OS X and Linux. The Sigma Chess web site contains a list of UCI chess engines for Mac OS X.

The Engine Manager

Before a UCI engine can be used within Sigma Chess, the engine must first be "installed". Installation and configuration of UCI engines is done from the new Engine Manager dialog shown below:

The Engine Manager Dialog

The Engine Manager dialog is opened from the new Engine submenu at the top of the Analyze menu.

A new UCI engine is installed by clicking the Add... button and then locating the engine application on your hard disk. The engine is launched and the various options for the engine will be listed in the Options list. The screenshot above shows the Engine Manager dialog after the HIARCS UCI engine has been installed.

The popup menu at the top of the dialog shows the currently selected engine. When the dialog is closed, this will be used as the default engine in new game windows (therefore the built-in Sigma engine is also included in the list, although it's not a UCI engine).

You can remove the currently selected UCI engine by clicking the Remove button. Note, that this will not physically delete the engine from your hard disk; it will merely be removed from Sigma's list of engines.

Loading UCI Engines

A UCI Engine is a command line Unix application, and is loaded on demand by the UCI Loader application. The UCI Loader subsequently establishes and maintains the connection between Sigma Chess and the engine.

Engine Options

The options for the currently selected UCI engine can be changed by first selecting an option in the list and then changing via the controls below the list. Options which can be changed from the Sigma Chess menus and dialogs are not included in the option list. This is the case with the Ponder option (which corresponds to Sigma's Permanent Brain option), and the playing strength options UCI_LimitStrength and UCI_Elo (which can be set from Sigma's Rating dialog).

The Default Options button reverts all options for the currently selected engine back to their default values.

There are many UCI options besides those described here. A more complete list is given at: http://www.lokasoft.nl/uploads/206/uci.rtf and an annotated description of the more common options is provided here: http://www.uciengines.de/UCI_Protocol/uci_protocol.html

MultiPV

Sigma 6.1.6 supports the MultiPV UCI option, which allows you to see the engine evaluations and principal variations (PVs) from the "k" highest ranked candidate moves. The MultiPV cannot be changed from the Engine Manager dialog. Instead you can increment/decrement "k" with the +/- buttons on the lower border of the analysis pane in the game window, to the left of the text stating either "Single PV" or "Multiple PV". These buttons are greyed out when the current number of variations is either the maximum or minimum number possible (or the engine isn't supporting MultiPV). Another term for multiPV is "k-var", for "k-variations".

Macintosh UCI engines supporting MultiPV include: Deep Sjeng, Fruit 2.2.1, HIARCS 11.1 (registered) Homer, Ruffian and Toga.

Engine Matches

Sigma Chess can host matches between UCI engines. The Engine Match... command from the Analyze menu opens the following dialog:

The Engine Match Dialog

You can select the two engines, the number of games to play, time controls, adjudication etc. It is also possible to save the games in a collection. You can create a new empty collection, open an existing one, or choose a collection which is already open (if any).

Nalimov Tables

Nalimov tables are like Sigma's endgame databases, but many more endgames are available. Nalimov tables require both Sigma Chess Pro and a compatible UCI engine, such as the registered version of HIARCS.

A UCI engine can use Nalimov tables if NalimovCache appears in the Engine Manager Options list.

You must tell the UCI engine where the Nalimov table files are by clicking the Browse... button next to the Nalimov Path field in the Engine Manager dialog box. Avoid putting the Nalimov tables in a folder protected by the OS/X FileVault security feature - it slows down disk access. Engines must index Nalimov tables before using them. The first time this happens after your computer is restarted, this will cause startup to take longer than otherwise.

An excellent discussion of the Nalimov tables, their use and where to download/buy them, is at http://horizonchess.com/FAQ/Winboard/egtb.html.

The Nalimov tables take 30 Mb to 24 Gb of disk space, depending on how many you install. The 3-4 piece tables are 30 Mb, a reasonable download for a fast Internet connection. The 3-4 tables and the most important 5-man tables fill four CDs. The full 3-4-5 tables (290 files, 7.05 Gb) fill 9 CDs or 1 DVD.

HIARCS for Macintosh has been tested with the "Nalimov Ending Tablebases, Complete Set, DVD" (all 3-4-5 piece tables), from store.convekta.com in the Database and Chess Data section ($26 US). It has also been tested with the 23+ Gb set of 3-4-5 + selected 6-man tables available from ChessBase at www.chessbase.com as "DVD Endgame Turbo 2" on 5 DVDs ($56 US). Just copy the tables you want (such as the "TBS" folder on the Convekta DVD) to your hard drive. Nalimov table filenames end in ".emd"

The built-in Sigma Chess engine currently doesn't support Nalimov tables.