Tie-Breaking

For reference, see the module tiebreaking.

We provide several ways to break ties between several projects. All tie-breaking rules are instantiations of the TieBreakingRule class. This class defines two functions untie and order that respectively return a single project from a set of several or order a list of projects.

We profile several tie-breaking rules.

from pabutools.election import Project, Instance, ApprovalProfile, ApprovalBallot
from pabutools.tiebreaking import max_cost_tie_breaking, min_cost_tie_breaking
from pabutools.tiebreaking import app_score_tie_breaking, lexico_tie_breaking

p = [Project("p0", 1), Project("p1", 2), Project("p2", 1)]
instance = Instance(p, budget_limit=2)
profile = ApprovalProfile([
    ApprovalBallot(p),
    ApprovalBallot(p[1:]),
    ApprovalBallot({p[1]})
])

min_cost_tie_breaking.untie(instance, profile, [p[0], p[1]])   # Returns p0
max_cost_tie_breaking.untie(instance, profile, [p[0], p[1]])   # Returns p1

app_score_tie_breaking.untie(instance, profile, p)   # Returns p1
app_score_tie_breaking.order(instance, profile, p)   # Returns [p1, p2, p0]

lexico_tie_breaking.order(instance, profile, p)   # Returns [p0, p1, p2]

These are mainly used as arguments for the rules, as seen above.