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Denis Pisarev
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* change (CI): markdown link checker * Fix some invalid doc links (re-run of cargo-unleash gen-readme w/ fixes). * Fix some invalid doc links * Fix some invalid doc links * Fix some links * Fix some links * Apply @bkchr suggestions from code review Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com> * Fix more links * Fix more links * typo * Fix more links * Fix more links * Ignore valid link .. check wrongly sees it as invalid * Fix style issue * Fix style issue * change (CI): update style guide link * change (lib): suggestions Co-authored-by: Dan Forbes <dan@danforbes.dev> Co-authored-by: Steve Degosserie <steve@parity.io> Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
59 lines
2.7 KiB
Markdown
59 lines
2.7 KiB
Markdown
A set of election algorithms to be used with a substrate runtime, typically within the staking
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sub-system. Notable implementation include:
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- [`seq_phragmen`]: Implements the Phragmén Sequential Method. An un-ranked, relatively fast
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election method that ensures PJR, but does not provide a constant factor approximation of the
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maximin problem.
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- [`phragmms`]: Implements a hybrid approach inspired by Phragmén which is executed faster but
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it can achieve a constant factor approximation of the maximin problem, similar to that of the
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MMS algorithm.
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- [`balance_solution`]: Implements the star balancing algorithm. This iterative process can push
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a solution toward being more `balances`, which in turn can increase its score.
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### Terminology
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This crate uses context-independent words, not to be confused with staking. This is because the
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election algorithms of this crate, while designed for staking, can be used in other contexts as
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well.
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`Voter`: The entity casting some votes to a number of `Targets`. This is the same as `Nominator`
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in the context of staking. `Target`: The entities eligible to be voted upon. This is the same as
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`Validator` in the context of staking. `Edge`: A mapping from a `Voter` to a `Target`.
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The goal of an election algorithm is to provide an `ElectionResult`. A data composed of:
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- `winners`: A flat list of identifiers belonging to those who have won the election, usually
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ordered in some meaningful way. They are zipped with their total backing stake.
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- `assignment`: A mapping from each voter to their winner-only targets, zipped with a ration
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denoting the amount of support given to that particular target.
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```rust
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// the winners.
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let winners = vec![(1, 100), (2, 50)];
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let assignments = vec![
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// A voter, giving equal backing to both 1 and 2.
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Assignment {
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who: 10,
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distribution: vec![(1, Perbill::from_percent(50)), (2, Perbill::from_percent(50))],
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},
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// A voter, Only backing 1.
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Assignment { who: 20, distribution: vec![(1, Perbill::from_percent(100))] },
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];
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// the combination of the two makes the election result.
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let election_result = ElectionResult { winners, assignments };
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```
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The `Assignment` field of the election result is voter-major, i.e. it is from the perspective of
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the voter. The struct that represents the opposite is called a `Support`. This struct is usually
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accessed in a map-like manner, i.e. keyed vy voters, therefor it is stored as a mapping called
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`SupportMap`.
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Moreover, the support is built from absolute backing values, not ratios like the example above.
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A struct similar to `Assignment` that has stake value instead of ratios is called an
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`StakedAssignment`.
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More information can be found at: https://arxiv.org/abs/2004.12990
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License: Apache-2.0 |