pumpkin_core/branching/variable_selection/
occurrence.rs

1use log::warn;
2
3use crate::branching::brancher::BrancherEvent;
4use crate::branching::tie_breaking::Direction;
5use crate::branching::tie_breaking::InOrderTieBreaker;
6use crate::branching::tie_breaking::TieBreaker;
7use crate::branching::variable_selection::VariableSelector;
8use crate::branching::SelectionContext;
9use crate::engine::variables::DomainId;
10use crate::pumpkin_assert_eq_simple;
11
12/// A [`VariableSelector`] which selects the variable with the largest number of attached
13/// constraints (where the provided `num_occurrences` stores the number of
14/// attached constraints per variable).
15pub struct Occurrence<Var, TieBreaking> {
16    variables: Vec<Var>,
17    tie_breaker: TieBreaking,
18    num_occurrences: Vec<u32>,
19}
20
21impl<Var, TieBreaking> std::fmt::Debug for Occurrence<Var, TieBreaking> {
22    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
23        f.debug_struct("Occurrence").finish()
24    }
25}
26
27impl<Var: Copy> Occurrence<Var, InOrderTieBreaker<Var, u32>> {
28    pub fn new(variables: &[Var], num_occurrences: &[u32]) -> Self {
29        pumpkin_assert_eq_simple!(
30            variables.len(), num_occurrences.len(),
31            "The number of variables and the number of elements in num_occurrences for the Occurence variable selector should be the same"
32        );
33        if variables.is_empty() {
34            warn!("The Occurence variable selector was not provided with any variables");
35        }
36        Occurrence {
37            variables: variables.to_vec(),
38            tie_breaker: InOrderTieBreaker::new(Direction::Maximum),
39            num_occurrences: num_occurrences.to_vec(),
40        }
41    }
42}
43
44impl<TieBreaking> VariableSelector<DomainId> for Occurrence<DomainId, TieBreaking>
45where
46    TieBreaking: TieBreaker<DomainId, u32>,
47{
48    fn select_variable(&mut self, context: &mut SelectionContext) -> Option<DomainId> {
49        self.variables
50            .iter()
51            .enumerate()
52            .filter(|(_, variable)| !context.is_integer_fixed(**variable))
53            .for_each(|(index, variable)| {
54                self.tie_breaker
55                    .consider(*variable, self.num_occurrences[index])
56            });
57        self.tie_breaker.select()
58    }
59
60    fn subscribe_to_events(&self) -> Vec<BrancherEvent> {
61        vec![]
62    }
63}
64
65#[cfg(test)]
66mod tests {
67    use super::*;
68    use crate::basic_types::tests::TestRandom;
69
70    #[test]
71    fn test_correctly_selected() {
72        let (assignments, _) = SelectionContext::create_for_testing(vec![(0, 10), (10, 20)]);
73        let mut test_rng = TestRandom::default();
74        let mut context = SelectionContext::new(&assignments, &mut test_rng);
75        let integer_variables = context.get_domains().collect::<Vec<_>>();
76
77        let mut strategy = Occurrence::new(&integer_variables, &[2, 1]);
78        let selected = strategy.select_variable(&mut context);
79        assert!(selected.is_some());
80        assert_eq!(selected.unwrap(), integer_variables[0])
81    }
82
83    #[test]
84    fn fixed_variables_are_not_selected() {
85        let (assignments, _) = SelectionContext::create_for_testing(vec![(10, 10), (20, 20)]);
86        let mut test_rng = TestRandom::default();
87        let mut context = SelectionContext::new(&assignments, &mut test_rng);
88        let integer_variables = context.get_domains().collect::<Vec<_>>();
89
90        let mut strategy = Occurrence::new(&integer_variables, &[1, 2]);
91        let selected = strategy.select_variable(&mut context);
92        assert!(selected.is_none());
93    }
94}
pumpkin_core/branching/variable_selection/occurrence.rs

pumpkin_core/branching/variable_selection/
occurrence.rs
