[Bug]: enumpoly hanging on 6x6 bimatrix game #1055

Where did you find this bug?

PyGambit

What operating system are you using?

macOS

What version of Gambit are you using?

Development version

What happened?

The bug is shown in the following example code where we load a 6x6 bimatrix game with 75 equilibria from the catalog.

Using enummixed_solve we find all 75 equilibria, but in the below code with enumpoly_solve, after creating an EFG version of the bimatrix game we then struggle to find the:

• 54 equilibria with use_strategic=True (but finding 53 is fine);
• 1 equilibrium with with use_strategic=False.

We find the same with the "small payoff" version of this game (slug: "6x6_game_with_75_eq_small_payoffs").

import pygambit as gbt
from tests.games import create_efg_corresponding_to_bimatrix_game  

slug = "journals/dcg/vonstengel1999/6x6_game_with_75_eq"
A, B = gbt.catalog.load(slug).to_arrays()
g = create_efg_corresponding_to_bimatrix_game(A, B, "")

#######################
# use_strategic is True
#######################

# Runs in ~ 10 seconds:
print(gbt.nash.enumpoly_solve(g, stop_after=53, use_strategic=True))

# Hangs:
# print(gbt.nash.enumpoly_solve(g, stop_after=54, use_strategic=True))

########################
# use_strategic is False
########################

# Hangs:
# print(gbt.nash.enumpoly_solve(g, stop_after=1, use_strategic=False))