pumpkin_solver/branching/variable_selection/
largest.rs

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
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
use log::warn;

use crate::branching::Direction;
use crate::branching::InOrderTieBreaker;
use crate::branching::SelectionContext;
use crate::branching::TieBreaker;
use crate::branching::VariableSelector;
use crate::engine::variables::DomainId;
use crate::pumpkin_assert_eq_simple;

/// A [`VariableSelector`] which selects the variable with the largest value in its domain.
///
/// Uses a [`TieBreaker`] to break ties, the default is the [`InOrderTieBreaker`] but it is
/// possible to construct the variable selector with a custom [`TieBreaker`] by using the
/// method [`Largest::with_tie_breaker`].
pub struct Largest<Var, TieBreaking> {
    variables: Vec<Var>,
    tie_breaker: TieBreaking,
}

impl<Var, TieBreaking> std::fmt::Debug for Largest<Var, TieBreaking> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("Largest").finish()
    }
}

impl<Var: Clone + 'static> Largest<Var, InOrderTieBreaker<Var, i32>> {
    pub fn new(variables: &[Var]) -> Self {
        if variables.is_empty() {
            warn!("The Largest variable selector was not provided with any variables");
            return Largest {
                variables: vec![],
                tie_breaker: InOrderTieBreaker::new(Direction::Maximum),
            };
        }
        Self {
            variables: variables.to_vec(),
            tie_breaker: InOrderTieBreaker::new(Direction::Maximum),
        }
    }
}

impl<Var: Clone + 'static, TieBreaking: TieBreaker<Var, i32>> Largest<Var, TieBreaking> {
    pub fn with_tie_breaker(variables: &[Var], tie_breaker: TieBreaking) -> Self {
        pumpkin_assert_eq_simple!(
            tie_breaker.get_direction(),
            Direction::Maximum,
            "The provided tie-breaker to Largest attempts to find the Minimum value
             instead of the Maximum value, please ensure that you have passed the correct tie-breaker");
        if variables.is_empty() {
            warn!("The Largest variable selector was not provided with any variables");
            return Largest {
                variables: vec![],
                tie_breaker,
            };
        }

        Self {
            variables: variables.to_vec(),
            tie_breaker,
        }
    }
}

impl<TieBreaking> VariableSelector<DomainId> for Largest<DomainId, TieBreaking>
where
    TieBreaking: TieBreaker<DomainId, i32>,
{
    fn select_variable(&mut self, context: &SelectionContext) -> Option<DomainId> {
        self.variables
            .iter()
            .filter(|variable| !context.is_integer_fixed(**variable))
            .for_each(|variable| {
                self.tie_breaker
                    .consider(*variable, context.upper_bound(*variable));
            });
        self.tie_breaker.select()
    }
}

#[cfg(test)]
mod tests {
    use crate::basic_types::tests::TestRandom;
    use crate::branching::Largest;
    use crate::branching::SelectionContext;
    use crate::branching::VariableSelector;

    #[test]
    fn test_correctly_selected() {
        let (mut assignments_integer, assignments_propositional) =
            SelectionContext::create_for_testing(2, 0, Some(vec![(0, 10), (5, 20)]));
        let mut test_rng = TestRandom::default();
        let integer_variables = assignments_integer.get_domains().collect::<Vec<_>>();
        let mut strategy = Largest::new(&integer_variables);

        {
            let context = SelectionContext::new(
                &assignments_integer,
                &assignments_propositional,
                &mut test_rng,
            );

            let selected = strategy.select_variable(&context);
            assert!(selected.is_some());
            assert_eq!(selected.unwrap(), integer_variables[1]);
        }

        let _ = assignments_integer.tighten_upper_bound(integer_variables[1], 9, None);

        let context = SelectionContext::new(
            &assignments_integer,
            &assignments_propositional,
            &mut test_rng,
        );

        let selected = strategy.select_variable(&context);
        assert!(selected.is_some());
        assert_eq!(selected.unwrap(), integer_variables[0]);
    }

    #[test]
    fn fixed_variables_are_not_selected() {
        let (assignments_integer, assignments_propositional) =
            SelectionContext::create_for_testing(2, 0, Some(vec![(10, 10), (20, 20)]));
        let mut test_rng = TestRandom::default();
        let context = SelectionContext::new(
            &assignments_integer,
            &assignments_propositional,
            &mut test_rng,
        );
        let integer_variables = context.get_domains().collect::<Vec<_>>();

        let mut strategy = Largest::new(&integer_variables);
        let selected = strategy.select_variable(&context);
        assert!(selected.is_none());
    }
}