Lc0 v0.19.0-rc1 (UPD: rc2) has been released.

The release candidate of a new Leela version has been released:

(v0.19.0-rc1)
Upd: we are releasing v0.19.0-rc2 immediately as due to mistake in the release procedure rc1 reported its version as v0.19.0-dev rather than v0.19.0-rc1

We expect testing phase to last around 7-10 days, after which proper v0.19.0 will be released.

Download here. Please test it thoroughly and report any bugs that you find.
Note: CudNN builds for Windows are now compiled with CUDA 10. You may need to update you GPU driver to run it.

Please don’t use release candidates to generate training games. We only use stable versions for that.

What’s new:

Search algorithm changes

When visiting terminal nodes and collisions, instead of counting that as one visit, estimate how many subsequent visits will also go to the same node, and do a batch update.

That should slightly improve nps near terminal nodes and in multithread configurations. Command line parameters that control that:

• --max-collision-events – number of collision events allowed per batch. Default is 32. This parameter is roughly equivalent to --allowed-node-collisions in v0.18.
• --max-collision-visits – total number of estimated collisions per NN batch. Default is 9999.

Time management

• Multiple changes have been done to make Leela track used time more precisely (particularly, the moment when to start timer is now much closer to the moment GUIs start timer).
• For smart pruning, Leela’s timer only starts when the first batch comes from NN eval. That should help against instamoves, especially on non-even GPUs.
• Also Leela stops the search quicker now when it sees that time is up (it could continue the search for hundreds of milliseconds after that, which caused time trouble if opponent moves very fast).

Those changes should help a lot in ultra-bullet configurations.

Better logging

Much more information is outputted now to the log file. That will allow us to easier diagnose problems if they occur. To have debug file written, add a command line option:

--logfile=/path/to/logfile

(or short option “-l /path/to/logfile”, or corresponding UCI option “LogFile”)

It’s recommended to always have logging on, to make it easier to report bugs when it happens.

Configuration parameters change

Large part of parameter handling has been reworked. As the result:

• All UCI parameters have been changed to have more “classical” look.
  E.g. was “Network weights file path”, became “WeightsFile”.

• Much more detailed help is shown than before when you run
  ./lc0 –help

• Some flags have been renamed, e.g.
  --futile-move-aversion
  is renamed back to
  --smart-pruning-factor.

• After setting a parameter (using command line parameter or uci setoption command), uci command “uci” shows updated result. That way you can check the current option values.

• Some command-line and UCI options are hidden now. Use --show-hidden command line parameter to unhide them. E.g.
  ./lc0 –show-hidden –help

Also, in selfplay mode the per player configuration format has been changed (although probably noone knew that anyway):
Was: ./lc0 selfplay player1: –movetime=14
Became: ./lc0 selfplay –player1.movetime=14

Other

• “go depth X” uci command now causes search to stop when depth information in uci info line reaches X. Not that it makes much sense for it to work this way, but at least it’s better than noting.

• Network file size can now be larger than 64MB.

• There is now an experimental flag --ramlimit-mb. The engine tries to estimate how much memory it uses and stops search when tree size (plus cache size) reaches RAM limit. The estimation is very rough. We’ll see how it performs and improve estimation later.
  In situations when search cannot be stopped (go infinite or ponder), bestmove is not automatically outputted. Instead, search stops progress and outputs warning.

• Benchmark mode has been implemented. Run run, use the following command line:
  ./lc0 benchmark
  This feature is pretty basic in the current version, but will be expanded later.

• As Leela plays much weaker in positions without history, it now is able to synthesize it and do not blunder in custom FEN positions. There is a --history-fill flag for it. Setting it to “no” disables the feature, setting to “fen_only” (default) enables it for all positions except chess start position, and setting it to “always” enables it even for startpos.

• Instead of output current win estimation as centipawn score approximation, Leela can how show it’s raw score. A flag that controls that is --score-type. Possible values:

  • centipawn (default) – approximate the win rate in centipawns, like Leela always did.
  • win_percentage – value from 0 to 100.0 which represents expected score in percents.
  • Q – the same, but scales from -100.0 to 100.0 rather than from 0 to 100.0