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GNU Go Documentation

3.9.3 Other options affecting strength and speed

• `--level amount'

  The higher the level, the deeper GNU Go reads. Level 10 is the default. If GNU Go plays too slowly on your machine, you may want to decrease it.

This single parameter `--level' is the best way of choosing whether to play stronger or faster. It controls a host of other parameters which may themselves be set individually at the command line. The default values of these parameters may be found by running gnugo --help.

Unless you are working on the program you probably don't need these options. Instead, just adjust the single variable `--level'. The remaining options are of use to developers tuning the program for performance and accuracy.

• `-D', `--depth depth'

  Deep reading cutoff. When reading beyond this depth (default 16) GNU Go assumes that any string which can obtain 3 liberties is alive. Thus GNU Go can read ladders to an arbitrary depth, but will miss other types of capturing moves.

• `--branch-depth'

  This sets the branch_depth, typically a little below the depth. Between branch_depth and depth, attacks on strings with 3 liberties are considered but branching is inhibited, so fewer variations are considered.

• `-B', `--backfill-depth depth'

  Deep reading cutoff. Beyond this depth (default 12) GNU Go will no longer try backfilling moves in its reading.

• `--backfill2-depth depth'

  Another depth controlling how deeply GNU Go looks for backfilling moves. The moves tried below backfill2_depth are generally more obscure and time intensive than those controlled by backfill_depth, so this parameter has a lower default.

• `-F', `--fourlib-depth depth'

  Deep reading cutoff. When reading beyond this depth (default 7) GNU Go assumes that any string which can obtain 4 liberties is alive.

• `-K', `--ko-depth depth'

  Deep reading cutoff. Beyond this depth (default 8) GNU Go no longer tries very hard to analyze kos.

• `--branch-depth depth'

  Deep reading cutoff. Below this depth (default 8), GNU Go still tries to attack strings with only 3 liberties, but only tries one move at each node.

• `--aa_depth depth'

  The reading function atari_atari looks for combinations beginning with a series of ataris, and culminating with some string having an unexpected change in status (e.g. alive to dead or critical). This command line optio sets the parameter aa_depth which determines how deeply this function looks for combinations.

• `--superstring-depth'

  A superstring (see section 14.7 Superstrings) is an amalgamation of tightly strings. Sometimes the best way to attack or defend a string is by attacking or defending an element of the superstring. Such tactics are tried below superstring_depth and this command line option allows this parameter to be set.

The preceeding options are documented with the reading code (see section 14.1 Reading Basics).

• `--owl-branch' Below this depth Owl only considers one move. Default 8.
• `--owl-reading' Below this depth Owl assumes the dragon has escaped. Default 20.
• `--owl-node-limit'

  If the number of variations exceeds this limit, Owl assumes the dragon can make life. Default 1000. We caution the user that increasing owl_node_limit does not necessarily increase the strength of the program.