wybr 0.0.6

Collection of preferential voting methods
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111

//! Common types

///Errors which may happen during the election
pub enum ElectionError {
    ///Scores got too large to fit in 64-bit integers
    ArithmeticOverflow,
    ///Too many digits requested for fixed-point operation to fit in 64-bit integers
    FixedPointDigitsTooMany,
    ///The election graph got degenerated and there is no single winner
    DegeneratedElectionGraph,
    ///There is not enough candidates to fill all seats
    NotEnoughCandidates,
}

use std::error::Error;
impl Error for ElectionError {}

use std::fmt;
impl fmt::Debug for ElectionError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self)
    }
}
impl fmt::Display for ElectionError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        use self::ElectionError::*;
        match self {
            FixedPointDigitsTooMany => write!(f, "Too many fixed-point digits"),
            DegeneratedElectionGraph => write!(f, "Beat graph is degenerated"),
            NotEnoughCandidates => write!(f, "Not enough candidates or votes"),
            ArithmeticOverflow => write!(f, "Arithmetic overflow"),
        }
    }
}

#[derive(Copy, Clone)]
///Method of scoring candidates in pair comparisons
pub enum PairScore {
    ///Winning votes; winner gets score equal to votes for them, looser gets 0.
    Winning,
    ///Margin of votes; winner gets winner votes - looser votes, looser gets looser votes - winner
    ///votes (that is, - winner score).
    Margin,
    ///Opposition; both winner and looser get their votes.
    Opposition,
}

#[derive(Copy, Clone)]
///Quota calculation method
pub enum Quota {
    ///[Hare quota](https://en.wikipedia.org/wiki/Hare_quota), that is useful votes / number of seats.
    ///Favours vote transfers, proportionality and diversity.
    Hare,
    ///Floor of the `Hare` value
    HareInt,
    ///[Droop quota](https://en.wikipedia.org/wiki/Droop_quota), that is floor( useful votes / ( seats + 1 ) ) + 1 vote.
    ///Favours first preferences, parties and secures majorities.
    Droop,
    ///[Hagenbach-Bischoff quota](https://en.wikipedia.org/wiki/Hagenbach-Bischoff_quota), that is useful votes / ( seats + 1 ).
    ///Similar to Droop, secures majorities perfectly.
    HagenbachBischoff,
}

#[derive(Clone, Copy)]
///Kind of a formula for scoring votes at different ranks
pub enum BordaKind {
    ///max_rank for first, 0 for last (1 for first if max_rank is 0)
    Borda0,
    ///max_rank+1 for first, 1 for last
    Borda1,
    ///1 for first, 1/(max_rank+1) for last; in practice multiplied by lcm(1,2,..,max_rank+1) so that all scores are integers
    Nauru,
}

#[derive(Clone, Copy)]
///Schwarz or Smith set selector
pub enum SetType {
    /// Smith set
    Smith,
    /// Schwartz set
    Schwartz,
}

#[doc(inline)]
pub use crate::tally::Transfer;

pub use crate::outcome::Outcome;

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn election_error_msg() {
        assert_eq!(
            format!("{:?}", ElectionError::ArithmeticOverflow),
            "Arithmetic overflow"
        );
        assert_eq!(
            format!("{:?}", ElectionError::FixedPointDigitsTooMany),
            "Too many fixed-point digits"
        );
        assert_eq!(
            format!("{:?}", ElectionError::NotEnoughCandidates),
            "Not enough candidates or votes"
        );
        assert_eq!(
            format!("{:?}", ElectionError::DegeneratedElectionGraph),
            "Beat graph is degenerated"
        );
    }
}