Restore standard passed pawn definition

[stockfish] / Readme.md

diff --git a/Readme.md b/Readme.md
index d4ea7a0f608620797f6881e54eba485fcf7a568e..a85e049ae2a0ae7af08f6c10e49e15048b587de2 100644 (file)
--- a/Readme.md
+++ b/Readme.md
@@ -1,5 +1,7 @@
 ### Overview
 
+[![Build Status](https://travis-ci.org/official-stockfish/Stockfish.svg?branch=master)](https://travis-ci.org/official-stockfish/Stockfish)
+
 Stockfish is a free UCI chess engine derived from Glaurung 2.1. It is
 not a complete chess program and requires some UCI-compatible GUI
 (e.g. XBoard with PolyGlot, eboard, Arena, Sigma Chess, Shredder, Chess
@@ -12,6 +14,8 @@ to one search thread, so it is therefore recommended to inspect the value of
 the *Threads* UCI parameter, and to make sure it equals the number of CPU
 cores on your computer.
 
+This version of Stockfish has support for Syzygybases.
+
 
 ### Files
 
@@ -25,6 +29,58 @@ This distribution of Stockfish consists of the following files:
     that can be used to compile Stockfish on Unix-like systems.
 
 
+### Syzygybases
+
+**Configuration**
+
+Syzygybases are configured using the UCI options "SyzygyPath",
+"SyzygyProbeDepth", "Syzygy50MoveRule" and "SyzygyProbeLimit".
+
+The option "SyzygyPath" should be set to the directory or directories that
+contain the .rtbw and .rtbz files. Multiple directories should be
+separated by ";" on Windows and by ":" on Unix-based operating systems.
+**Do not use spaces around the ";" or ":".**
+
+Example: `C:\tablebases\wdl345;C:\tablebases\wdl6;D:\tablebases\dtz345;D:\tablebases\dtz6`
+
+It is recommended to store .rtbw files on an SSD. There is no loss in
+storing the .rtbz files on a regular HD.
+
+Increasing the "SyzygyProbeDepth" option lets the engine probe less
+aggressively. Set this option to a higher value if you experience too much
+slowdown (in terms of nps) due to TB probing.
+
+Set the "Syzygy50MoveRule" option to false if you want tablebase positions
+that are drawn by the 50-move rule to count as win or loss. This may be useful
+for correspondence games (because of tablebase adjudication).
+
+The "SyzygyProbeLimit" option should normally be left at its default value.
+
+**What to expect**
+If the engine is searching a position that is not in the tablebases (e.g.
+a position with 7 pieces), it will access the tablebases during the search.
+If the engine reports a very large score (typically 123.xx), this means
+that it has found a winning line into a tablebase position.
+
+If the engine is given a position to search that is in the tablebases, it
+will use the tablebases at the beginning of the search to preselect all
+good moves, i.e. all moves that preserve the win or preserve the draw while
+taking into account the 50-move rule.
+It will then perform a search only on those moves. **The engine will not move
+immediately**, unless there is only a single good move. **The engine likely
+will not report a mate score even if the position is known to be won.**
+
+It is therefore clear that behaviour is not identical to what one might
+be used to with Nalimov tablebases. There are technical reasons for this
+difference, the main technical reason being that Nalimov tablebases use the
+DTM metric (distance-to-mate), while Syzygybases use a variation of the
+DTZ metric (distance-to-zero, zero meaning any move that resets the 50-move
+counter). This special metric is one of the reasons that Syzygybases are
+more compact than Nalimov tablebases, while still storing all information
+needed for optimal play and in addition being able to take into account
+the 50-move rule.
+
+
 ### Compiling it yourself
 
 On Unix-like systems, it should be possible to compile Stockfish
@@ -55,4 +111,4 @@ to where the source code can be found. If you make any changes to the
 source code, these changes must also be made available under the GPL.
 
 For full details, read the copy of the GPL found in the file named
-*Copying.txt*
+*Copying.txt*.