Pachi can refer to: a simple modular framework for programs playing the game of Go/Weiqi/Baduk, and a reasonably strong engine built within this framework.
The default engine plays by Chinese rules and should be about 7d KGS strength on 9x9. On 19x19 it can hold a solid KGS 2d rank on modest hardware (Raspberry Pi, dcnn) or faster machine (e.g. six-way Intel i7) without dcnn.
When using a large cluster (64 machines, 20 cores each), it maintains KGS 3d to 4d and has won e.g. a 7-stone handicap game against Zhou Junxun 9p.
By default, Pachi currently uses the UCT engine that combines Monte Carlo approach with tree search; UCB1AMAF tree policy using the RAVE method is used for tree search, while the Moggy playout policy using 3x3 patterns and various tactical checks is used for the semi-random Monte Carlo playouts. MM patterns are used in the tree search.
Windows: Download binary release for windows and follow instructions inside.
Ubuntu: There's a 'pachi-go' package in my ppa:
sudo add-apt-repository ppa:lemonsqueeze/pachi sudo apt-get update sudo apt-get install pachi-go
Performance might be better if you recompile for your own system though.
Currently Unix, Mac and Windows are supported.
To build Pachi, simply type:
DO NOT make the GTP interface accessible directly to untrusted users since the parser is not secure - see the HACKING file for details.
The pachi program can take many parameters, as well as the particular engine being used; the defaults should be fine for initial usage, see below for some more tips.
In case you hit compilation issues (e.g. when building on MacOS/X) or want to change the build configuration, check the user configurable section at the top of the Makefile.
Pachi can use a neural network as source of good moves to consider. With dcnn support Pachi can play at dan level strength on modest hardware. For large number of playouts this makes it about 1 stone stronger, and tends to make the games more pretty. A raw dcnn engine is available for pure dcnn play (not recommended for actual games, pachi won't know when to pass or resign !).
Currently dcnn is used for root node only, and pondering and dcnn can't be used together (you should get a warning on startup).
To build Pachi with DCNN support:
- Install Caffe
CPU only build is fine, no need for GPU, cuda or the other optional dependencies.
- Edit Makefile, set DCNN=1, point it to where caffe is installed and build.
Install dcnn files in current directory.
Detlef Schmicker's 54% dcnn can be found at:
More information about this dcnn here.
If you want to use a network with different inputs you'll have to tweak
dcnn.c to accomodate it. Pachi will check for
golast.trained files on startup and use them if present when
playing on 19x19.
How to run
By default Pachi will run on all cores, using up to 200Mb of memory for tree search and taking a little under 10 seconds per move. You can adjust these parameters by passing it extra command line options.
For main options description try:
Pachi can smartly deal with a variety of time settings (canadian byoyomi recommended to maximize efficient time allocation). However, most of these are accessible only via GTP, that is by the frontend keeping track of time, e.g. KGS or gogui.
It's also possible to force time settings via the command line (GTP time settings are ignored then):
pachi -t 2020s per move.
pachi -t _60010 minutes sudden death.
pachi -t =50005000 playouts per move.
pachi -t =5000:15000Think more when needed. Same but up-to 15000 playouts if best move is unclear.
pachi -t =5000:15000 --fuseki-time =4000Don't think too much during fuseki.
Pachi will play fast on a fast computer, slow on a slow computer, but strength will remain the same:
pachi -t =5000:15000kgs 2d with dcnn support.
pachi --nodcnn -t =5000kgs 3k (mcts only).
pachi resign_threshold=0.25Resign when winrate < 25% (default: 10%).
pachi -t 10 threads=4,max_tree_size=100
Play with 10s per move on 4 threads, taking up to 100Mb of memory (+ several tens Mb as a constant overhead).
pachi -t _1200 --nodcnn threads=8,max_tree_size=3072,pondering
Play without dcnn with time settings 20:00 S.D. on 8 threads, taking up to 3Gb of memory, and thinking during the opponent's turn as well.
For now, there is no comprehensive documentation of engine options, but you can get a pretty good idea by looking at the uct_state_init() function in uct/uct.c - you will find the list of UCT engine options there, each with a description. At any rate, usually the three options above are the only ones you really want to tweak.
Pachi logs details of its activity on stderr, which can be viewed via
Tools -> GTP Shell in gogui. Tons of details about winrates, memory usage,
score estimate etc can be found here. Even though most of it available through
other means in gogui, it's always a good place to look in case something
-d <log_level> changes the amount of logging (-d0 suppresses everything)
-o log_file logs to a file instead. gogui live-gfx commands won't work though.
Mostly useful when running without dcnn (dcnn can deal with fuseki).
Pachi can use an opening book in a Fuego-compatible format - you can obtain one at http://gnugo.baduk.org/fuegoob.htm and use it in Pachi with the -f parameter:
pachi -f book.dat ...
You may wish to append some custom Pachi opening book lines to book.dat; take them from the book.dat.extra file. If using the default Fuego book, you may want to remove the lines listed in book.dat.bad.
When running Pachi through GoGui, a number of graphic tools are available
Tools -> Analyze commands window:
- Best moves
- Score estimate
- DCNN ratings ...
It's also possible to visualize best moves / best sequence while Pachi is thinking via the live gfx commands.
There are some non-gui tools for game analysis as well, see below.
Mostly useful when running without dcnn
Normally, Pachi cares only for win or loss and does not take into account the point amount. This means that it will play slack endgame when winning and crazy moves followed with a resign when losing.
It may give you a more pleasurable playing experience if Pachi does take into account the point size, strives for a maximum (reasonable) win margin when winning and minimal point loss when losing. This is possible by using the maximize_score parameter, e.g.:
pachi -t _1200 threads=8,maximize_score
This enables an aggressive dynamic komi usage and end result margin is included in node values aside of winrate. Pachi will also enter scoring even when losing (normally, Pachi will never pass in that case). Note that if you pass any 'dynkomi' parameter to Pachi, you will reset the values set by 'maximize_score'.
Note that Pachi in this mode may be slightly weaker, and result margin should not be taken into account when judging either player's strength. During the game, the winning/losing margin can be approximated from Pachi's "extra komi" or "xkomi" reporting in the progress messages.
MM patterns have replaced the large patterns database used in previous versions. No need to download anything extra, they're enabled by default as long as Pachi can find its data files.
Patterns should load instantly now and take up very little memory. Prediction rate
in middle game is better too.
See pattern/README for details.
After compiling and setting up data files you can install pachi with:
make install make install-data
Pachi will look for extra data files (such as dcnn, pattern, joseki or
fuseki database) in pachi's system directory (
by default) as well as current directory. System data directory can be
overridden at runtime by setting
DATA_DIR environment variable.
Experiments and Testing
Except UCT, Pachi supports a simple
random idiotbot-like engine and an
montecarlo treeless MonteCarlo-player. The MonteCarlo simulation ("playout")
policies are also pluggable, by default we use the one that makes use of
heavy domain knowledge.
Other special engines are also provided:
distributedengine for cluster play; the description at the top of distributed/distributed.c should provide all the guidance
dcnnengine plays moves according to dcnn policy.
replayengine simply plays moves according to the playout policy suggestions
patternplayengine plays moves according to the learned patterns
- few other purely for development usage
Pachi can be used as a test opponent for development of other go-playing programs. For example, to get the "plainest UCT" player, use:
pachi -t =5000 --nodcnn policy=ucb1,playout=light,prior=eqex=0,dynkomi=none,pondering=0,pass_all_alive
This will fix the number of playouts per move to 5000, switch the node selection policy from ucb1amaf to ucb1 (i.e. disable RAVE), switch the playouts from heuristic-heavy moggy to uniformly random light, stop prioring the node values heuristically, turn off dynamic komi, disable thinking on the opponent's time and make sure Pachi passes only when just 10% alive stones remain on the board (to avoid disputes during counting).
You can of course selectively re-enable various features or tweak this further. But please note that using Pachi in this mode is not tested extensively, so check its performance in whatever version you test before you use it as a reference.
Note that even in this "basic UCT" mode, Pachi optimizes tree search by considering board symmetries at the beginning. Currently, there's no easy option to turn that off. The easiest way is to tweak board.c so that board_symmetry_update() has goto break_symmetry at the beginning and board_clear has board->symmetry.type = SYM_NONE.
Pachi can also help you analyze your games by being able to provide its opinion on various positions. The user interface is very rudimentary, but the ability is certainly there.
There are currently several Pachi interfaces provided for this purpose.
Pachi can evaluate all moves within a given game and show how
the winrates for both players evolved - i.e. who was winning at which
game stage. This is implemented using the
See the comment on top of the script about its usage.
Pachi can evaluate all available moves in a given situation and for each give a value between 0 and 1 representing perceived likelihood of winning the game if one would play that move. I.e. it can suggest which moves would be good and bad in a single given situation.
To achieve the latter, note the number of move at the situation you
want to evaluate and run the
See the comment on top of the script about its usage.
Pattern Move Hinting
Pachi can show instantenous pattern-based move suggestions very much like for example Moyo Go Studio (though of course without a GUI). You can use the Move Ranking method above (tools/sgf-ratemove.sh), but pass it an extra parameter '-e patternplay'.
The aim of the software framework is to make it easy to plug your engine to the common infrastructure and implement your ideas while minimalizing the overhead of implementing the GTP, speed-optimized board implementation, etc. Also, there are premade random playout and UCT tree engines, so that you can directly tweak only particular policies. The infrastructure is pretty fast and it should be quite easy for you (or us) to extend it to provide more facilities for your engine.
See the HACKING file for a more detailed developer's view of Pachi.
Also, if you are interested about Pachi's architecture, algorithms etc., consider taking a look at Petr Baudis' Master's Thesis:
...or a slightly newer scientific paper on Pachi:
Pachi is distributed under the GPLv2 licence (see the COPYING file for details and full text of the licence); you are welcome to tweak it as you wish (contributing back upstream is welcome) and distribute it freely, but only together with the source code. You are welcome to make private modifications to the code (e.g. try new algorithms and approaches), use them internally or even to have your bot play on the internet and enter competitions, but as soon as you want to release it to the public, you need to release the source code as well.
One exception is the Autotest framework, which is licenced under the terms of the MIT licence (close to public domain) - you are free to use it any way you wish.