The Program integrates the Syzygy table probing code © Ronald de Man, the Gaviota EGTB probing code © Miguel A. Ballicora and the Nalimov EGTB probing code © Eugene Nalimov.

 

Syzygy bases 

The Syzygy 6-men EGTB system is the recommended table base solution for Houdini.

 

It features by far the best compression (smallest file size) and best performance, especially when multiple threads perform simultaneous EGTB probing. Houdini has been extensively tuned for this state-of-the-art end game table base system so as to provide optimum precision and strength in the late endgame at any time control and with any number of cores. While installing the files on a SSD disk is recommended, the performance of the Syzygy on a normal hard disk is still very good.

 

The only drawback of Syzygy bases is that they do not contain the exact Distance to Mate information. If you require an exact mating distance in a position you'll need an alternative solution.

 

The Syzygy 6-men EGTB system is the recommended table base solution for Houdini.

 

For the Syzygy EGTB support you'll need to install the Syzygy EGTB files. At the time of writing all the Syzygy files are available for torrent download at http://oics.olympuschess.com/tracker/index.php. The 3-4-5-men Syzygy are also available for direct download at http://olympuschess.com/egtb/sbases.

 

The total size of the 3-4-5-men files is 938 MB (290 files), the 6-men table bases require 149 GB (730 files).

 

Nalimov EGTB

For the Nalimov EGTB support you'll need to install the Nalimov EGTB files.

 

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Question: I don't understand the concept of setting a depth for EGTB probing. Why wouldn't all positions that have 3-4-5 pieces probe the table bases to get the evaluation?

 

EGTB probes are extremely slow compared to a normal evaluation by the engine. Suppose you have a K+Q+P against K+N ending. Even without consulting the table bases Houdini knows that this ending is easily won for the K+Q+P side. Consulting the EGTB for this position would reduce Houdini's playing strength, as it could easily have evaluated 1,000 other positions instead of making the rather useless EGTB probe.

 

Even the in-memory "soft" Gaviota or Scorpio probes are sometimes relatively slow compared to a native evaluation of the position - especially when multiple threads are running. If two threads simultaneously perform a soft probe, the second thread has to wait for the first to finish its probe.

 

This is aggravated by the fact that Houdini contains a lot of end game knowledge in its native evaluation function - a lot more than most other chess engines. For example, even in a non-obvious ending like KBP v KB with bishops of the same color, Houdini knows quite well which positions are won and which are drawn. This means that except for difficult-to-evaluate endings like KQP v KQ the 5-men EGTB do not really increase Houdini's playing strength.

 

To handle this situation in an intelligent way, Houdini will vary the frequency at which the EGTB are probed depending on the actual end game that is occurring. In difficult-to-evaluate endings Houdini will probe the EGTB files much earlier than in endings that are easy to evaluate.

 

The frequency of the probing is further influenced by the following parameters:

 

· Hard Probe Depth is the earliest search depth at which the EGTB probing will result in a disk access. You can reduce this value if the table base files are installed on a very fast disk, or if you are running less than 4 threads.

 

· Soft Probe Depth is the earliest search depth for EGTB probing that uses only the memory cache. You can reduce this value if you are running less than 4 threads.