Counterfactual Regret (CFR)
===========================
[](https://crates.io/crates/cfr)
[](https://docs.rs/cfr)
[](LICENSE)
[](https://github.com/erikbrinkman/cfr/actions/workflows/rust.yml)
Counterfactual regret minimization solver for two-player zero-sum
incomplete-information games in rust. This is a rust library and binary for
computing approximate nash-equilibria of two-player zero-sum
incomplete-information games.
Usage
-----
### Library
To use the library part of this crate, add the following to your `Cargo.toml`.
```toml
[dependencies]
cfr = { version = "0.1.0", default-features = false }
```
Then implement
[`IntoGameNode`](https://docs.rs/cfr/latest/cfr/trait.IntoGameNode.html), for
a type that represents a node in your game tree (or alternatively can generate
new nodes).
Finally execute:
```rust
use cfr::{Game, IntoGameNode};
struct MyData { ... }
impl IntoGameNode for MyData { ... }
let game = Game::from_root(...)?;
let strategies = game.solve_external();
let info = strategies.get_info();
let regret = info.regret();
let [player_one, player_two] = strategies.as_named();
```
### Binary
This package can also be used as a binary with a few different input formats.
install it with
```bash
$ cargo install cfr
```
Solving a game will produce the expected utility to player one, as well as the
regrets and the strategy found in json format.
```bash
$ cfr -i game_file
{
"expected_one_utility": 0.05555555727916178,
"player_one_regret": 1.186075528125663e-06,
"player_two_regret": 8.061797025377127e-05,
"regret": 8.061797025377127e-05,
"player_one_strategy": { ... },
"player_two_regret": { ... }
}
```
The command line tool can interpret a custom [json dsl](#json-format), and
[gambit `.efg`](#gambit-format) files.
#### JSON Format
The DSL is defined by:
```bison
chance ::= {
"chance": {
"infoset"?: <string>,
"outcomes": {
"<named outcome>": { "prob": <number>, "state": node },
...
}
}
}
player ::= {
"player": {
"player_one": <bool>,
"infoset": <string>,
"actions": { "<named action>": node, ... }
}
}
```
A minimal example highlighting all types of nodes, but of an uninteresting game is:
```json
{
"chance": {
"outcomes": {
"single": {
"prob": 1.0,
"state": {
"player": {
"player_one": true,
"infoset": "none",
"actions": {
"only": {
"terminal": 0.0
}
}
}
}
}
}
}
}
```
In this game there's a 100% chance of the `"single"` outcome, followed by a
move by player one where they have information `"none"` and only have one
action: `"only"`. After selecting that action, they get payoff 0.
#### Gambit Format
The gambit format follows the standard [gambit extensive form game
format](https://gambitproject.readthedocs.io/en/v16.0.2/formats.html), with
some mild restrictions.
- Gambit specifies that actions are optional, but this requires every player and chance node specifies thier actions.
- Actions must be unique, and there are some very mild restrictions on
non-conflicting information set names (See [duplicate infosets](#duplicate-infosets)).
- The gambit format allows for arbitrary player, non-constant-sum extensive
form games, but this only allows two-player constant-sum perfect recall
games.
- For efficiency this uses double precision floats, because equilibria are
approximate, thus in extreme circumstances payoffs might not be
representable.
Examples
--------
If implementing
[IntoGameNode](https://docs.rs/cfr/latest/cfr/trait.IntoGameNode.html) is
confusing for your game, here are more complicated examples of games that don't
quite fit in the documentation:
- [Kuhn Poker](https://github.com/erikbrinkman/cfr/blob/main/examples/kuhn_poker.rs) - this
can also be run using `cargo run --example kuhn_poker --`.
- [Liar's Dice](https://github.com/erikbrinkman/cfr/blob/main/benches/liars_dice.rs) - this
is implemented as a benchmark to allow using nightly apis.
Errors
------
This section has more details on errors the command line might return.
### Json Error
This error occurs when the json doesn't match the expected format for reading.
See [JSON Format](#json-format) for details on the specification, and make sure
that the json you're providing matches that specification.
### Gambit Error
This error occurs when the gambit file can't be parsed. There should be more
info about exactly where the error occured. See [gambit format](#gambit-format)
for more details on the format.
### Auto Error
The game file couldn't be parsed by any known game format. In order to get more
detailed errors regarding the parsing failure, try rerunning again with
`--input-format <format>` to get more precise errors
### Duplicate Infosets
Gambit `.efg` files don't require naming infosets, but `cfr` requires string
names for every infoset. It will default to useing the string version of the
infoset number, but this will fail if that infoset name is already taken. For
example:
```
...
p 1 1 "2" { ... } 0
p 1 2 { ... } 0
...
```
will throw this error as long as a name for infoset 2 isn't defined elsewhere.
### Constant Sum
Counterfactual regret minimization only works on constant sum games. Since
gambit files define payoffs independently, this verifies that the range of the
sum of every profile is less than 0.1% of the range of the of the payoffs for a
single player. If you encounter this error, `cfr` will not for this game.
### Game Error
This error occurs if there were problems with the game specification that made
creating a compact game impossible. See the documentation of
[`GameError`](https://docs.rs/cfr/latest/cfr/enum.GameError.html) for more
details.
### Solve Error
The error occured if there were problems solving it. This should only happen if
you requested too many threads, or the threads couldn't be spawned. See the
documentation of
[`SolveError`](https://docs.rs/cfr/latest/cfr/enum.SolveError.html) for more
details.
To Do
-----
- [ ] With the implementation of discounted CFR, the incremental regret updates
hold even less frequrntly. We should instead check the true regret after a
certain number of iterations. This takes some restructuing, as well as some
benchmarking to make sure that time isn't wasted on regret calculation.
- [ ] We currently set the number of threads arbitrarily high, but we have the
full game tree before we decide how many threads to spawn, so we could be
smarter about both setting a maximum, and setting the load factor based on
the tree size.
- [ ] This currently requires that infosets and actions be hashable and,
depending on the usecase, cloneable. Most of the functions could be rewritten
to take combinations of `Hash`, `Ord`, or `Clone` and use the most performant
option given the trait bounds. This doesn't seem particularly useful and
would be a lot of work, so it's omitted for now.