frame_plugins::elections::fair

Struct PhragmenModel

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pub struct PhragmenModel;
Expand description

The Phragmen model ranks candidates based on fair distribution of voter/backer load. Each candidate has (Backer, Backed) pairs representing support, and the algorithm selects candidates sequentially to minimize the maximum load among all backers.

Concept: Proportional Load Balancing

This plugin supports multiple Phragmen variants through the plugin context PhragmenModelConfig:

  • Weighted vs unweighted contributions
  • Deterministic tie-breaking
  • Optional scaling of backer contributions

§Applications:

  • Governance elections with proportional representation
  • Token or stake weighted systems
  • Delegation or liquid democracy systems

§References:

  • Phragmen voting - Wikipedia
  • Enestrom, E. “Mathematical Theory of Proportional Representation”, 1896
  • Thiele, T. N., “Proportional Representation in Elections”, 1895

Trait Implementations§

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impl Debug for PhragmenModel

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fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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impl Default for PhragmenModel

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fn default() -> PhragmenModel

Returns the “default value” for a type. Read more
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impl<Candidate, FairWeight, Backer, Backed, Input, Output> PurePluginModel<Input, PhragmenModelConfig<Backed>, Output> for PhragmenModel
where Input: IntoIterator<Item = (Candidate, FairWeight)> + Clone, Output: FromIterator<Candidate>, FairWeight: IntoIterator<Item = (Backer, Backed)> + Clone, Backed: Clone + Zero + Add<Output = Backed> + Ord + Div<usize, Output = Backed> + Mul<Backed, Output = Backed>, Candidate: Clone + Eq, Backer: Clone + Eq + Hash + Ord,

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fn compute(&self, input: Input, ctx: &PhragmenModelConfig<Backed>) -> Output

Computes the Phragmen ranking of candidates imperatively.

Steps:

  1. Initialize all backer loads to zero.
  2. While candidates remain:
    • Compute maximum load increase for each candidate if elected.
    • Apply weighting/scaling if configured.
    • Deterministically select candidate with minimal max load (tie = first in list).
    • Update ranking and backer loads.
  3. Return all candidates in ranked order.

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