Idea 8 openspiel exporters/importers (#41)

Author: rahulsavani

content/gsoc_2026.md

@@ -30,15 +30,16 @@ Bernhard von Stengel can act as an additional mentor for ideas 3 and 6; Bernhard
 
 The following table summarises our ideas, and includes links to detailed descriptions below.
 
-| Idea/link                                                               | Title                                                             | Difficulty            | Keywords                                                             |
-| ----------------------------------------------------------------------  | ----------------------------------------------------------------- | --------------------- | -------------------------------------------------------------------- |
-| [1](#idea-1-updating-the-gambit-gui)                                    | Updating the Gambit GUI                                           | Medium                | GUI, visualization, C++, wxWidgets                                   |
-| [2](#idea-2-gameinterpreter-a-front-end-for-llm-based-game-translation)  | GameInterpreter: A front-end for LLM-based game translation       | Easy/Medium           | LLMs, extensive-form games, front-end                                |
-| [3](#idea-3-a-layout-algorithm-for-visualising-game-trees)              | A layout algorithm for visualising game trees                     | Hard                  | Extensive-form games, visualization, graph drawing                   |
-| [4](#idea-4-working-on-gambit-interoperability-with-sagemath)           | Working on Gambit interoperability with SageMath                  | Easy/Medium           | SageMath, interoperability, Python                                    |
-| [5](#idea-5-updating-how-gambit-works-with-external-solvers)    | Updating how Gambit works with external solvers             | Medium/Hard           | Nash equilibrium, mathematical optimization; linear complementarity  |
-| [6](#idea-6-development-and-integration-of-lemkes-algorithm-package)            | Development and integration of Lemke's algorithm package                | Medium/Hard           | Mathematical optimization; interoperability                          |
-| [7](#idea-7-new-algorithms-for-finding-nash-equilibria)                 | New algorithms for finding Nash equilibria                        | Medium/Hard           | Nash equilibrium, algorithms, mathematical optimization              |
+| Idea/link                                                               | Title                                                             | Difficulty            | Keywords                                                                   |
+| ----------------------------------------------------------------------  | ----------------------------------------------------------------- | --------------------- | -------------------------------------------------------------------------- |
+| [1](#idea-1-updating-the-gambit-gui)                                    | Updating the Gambit GUI                                           | Medium                | GUI, visualization, C++, wxWidgets                                         |
+| [2](#idea-2-gameinterpreter-a-front-end-for-llm-based-game-translation) | GameInterpreter: A front-end for LLM-based game translation       | Easy/Medium           | LLMs, extensive-form games, front-end                                      |
+| [3](#idea-3-a-layout-algorithm-for-visualising-game-trees)              | A layout algorithm for visualising game trees                     | Hard                  | Extensive-form games, visualization, graph drawing                         |
+| [4](#idea-4-working-on-gambit-interoperability-with-sagemath)           | Working on Gambit interoperability with SageMath                  | Easy/Medium           | SageMath, interoperability, Python                                         |
+| [5](#idea-5-updating-how-gambit-works-with-external-solvers)            | Updating how Gambit works with external solvers                   | Medium/Hard           | Nash equilibrium, mathematical optimization; linear complementarity        |
+| [6](#idea-6-development-and-integration-of-lemkes-algorithm-package)    | Development and integration of Lemke's algorithm package          | Medium/Hard           | Mathematical optimization; interoperability                                |
+| [7](#idea-7-new-algorithms-for-finding-nash-equilibria)                 | New algorithms for finding Nash equilibria                        | Medium/Hard           | Nash equilibrium, algorithms, mathematical optimization                    |
+| [8](#idea-8-extensive-form-game-efg-exporter-for-deepminds-openspiel)   | Extensive-form Game .efg exporter for DeepMind's OpenSpiel        | Easy                  | Extensive-form-game; normal-form game; .efg format; .nfg format; OpenSpiel |
 
 ### Idea 1: "Updating the Gambit GUI"
 
@@ -292,3 +293,54 @@ algorithms a student might choose to implement. Also, this project idea is only
 constrained by the existing Gambit code base, and thus the challenge is really on picking, 
 understanding, and then implementing an equilibrium computation method or methods, which can
 give rise to easy or hard projects, depending on the methods chosen.
+
+### Idea 8: "EFG/NFG exporters for DeepMind's OpenSpiel"
+
+#### Description
+
+[OpenSpiel](https://github.com/google-deepmind/open_spiel) is a collection of environments and algorithms for research in general reinforcement learning and search/planning in games created and maintained by Google DeepMind.
+
+OpenSpiel already supports export to Gambit's two primary game formats, namely the strategic, aka
+normal, form games (NFGs) and the extensive-form games (EFGs). However, these exporters a) have
+restrictions and b) are not well documented. In particular, even though OpenSpiel (and Gambit)
+supports payoffs at non-terminal nodes, the OpenSpiel exporters only work if all payoffs (aka
+rewards) are at terminal nodes.
+
+The idea here is to develop the existing exporters to make them more general, covering non-terminal payoffs,
+and also better documented.
+
+Here are pointers to the existing exporters (two for each type of game format):
+
+- [EFG exporter in python](https://github.com/google-deepmind/open_spiel/blob/master/open_spiel/python/algorithms/gambit.py)
+- [Independent EFG exporter in C++](https://github.com/google-deepmind/open_spiel/blob/master/open_spiel/game_transforms/efg_writer)
+- [NFG exporter written in C++](https://github.com/google-deepmind/open_spiel/blob/master/open_spiel/algorithms/nfg_writer.cc), 
+    exposed to Python and [tested](https://github.com/google-deepmind/open_spiel/blob/master/open_spiel/python/tests/nfg_writer_test.py)
+
+As a stretch goal, a student could work on an .efg importer after finishing the exporter. Again
+there is [one](https://github.com/google-deepmind/open_spiel/tree/master/open_spiel/games/efg_game/games) in OpenSpiel 
+but it does not support as many games as we would like.
+
+#### Expected outcomes
+
+The expected outcome of this project is a pull request to OpenSpiel that provides more general exporters.
+The new exporters should be well tested, including of course, on games with non-terminal payoffs.
+
+#### Skills required/preferred
+
+- Ideally the exporter would be written in C++ for speed, but extending the Python exporter would also be useful.
+So a student should be comfortable with C++ and/or Python.
+
+- It will be helpful if a student already knows what EFGs and NFGs are, which they would have learnt in any basic Game Theory course.
+
+#### Possible mentors: 
+
+[Rahul Savani](mailto:rahul.savani@gmail.com); [Ed Chalstrey](echalstrey@turing.ac.uk)
+
+#### Expected size of project (90, 175, or 350 hours)
+
+90 hours -- that should be enough for both EFG/NFG exporters, and ideally also importers for both, along with
+documentation and tests.
+
+#### Difficulty rating (easy/medium/hard)
+
+Easy.