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
138
139
140
141
142
143
144
145
146
147
use rand::Rng;
use crate::Genome;
use super::{MutationError, MutationResult, Mutations};
impl Mutations {
/// Removes a node and all incoming and outgoing connections, should this be possible without introducing dangling structure.
/// Dangling means the in- or out-degree of any hidden node is zero, i.e. it neither can receive nor propagate a signal.
/// If it is not possible, no node will be removed.
pub fn remove_node(genome: &mut Genome, rng: &mut impl Rng) -> MutationResult {
if let Some(removable_node) = &genome
.hidden
.iter()
// make iterator wrap
.cycle()
// randomly offset into the iterator to choose any node
.skip((rng.gen::<f64>() * (genome.hidden.len()) as f64).floor() as usize)
// just loop every value once
.take(genome.hidden.len())
.find(|removal_candidate| {
genome
.connections()
// find all input nodes of removal candidate
.filter_map(|connection| {
if connection.output == removal_candidate.id {
Some(connection.input)
} else {
None
}
})
// make sure they have an alternative output
.all(|id| genome.has_alternative_output(id, removal_candidate.id))
&& genome
.connections()
// find all output nodes of removal candidate
.filter_map(|connection| {
if connection.input == removal_candidate.id {
Some(connection.output)
} else {
None
}
})
// make sure they have an alternative input
.all(|id| genome.has_alternative_input(id, removal_candidate.id))
})
.cloned()
{
// remove all feed-forward connections involving the node to be removed
genome.feed_forward.retain(|connection| {
connection.input != removable_node.id && connection.output != removable_node.id
});
// remove all recurrent connections involving the node to be removed
genome.recurrent.retain(|connection| {
connection.input != removable_node.id && connection.output != removable_node.id
});
// remove the node to be removed
assert!(genome.hidden.remove(removable_node));
Ok(())
} else {
Err(MutationError::CouldNotRemoveNode)
}
}
}
#[cfg(test)]
mod tests {
use rand::thread_rng;
use crate::{
activations::Activation,
genes::{Connection, Genes, Id, Node},
mutations::MutationError,
Genome, Mutations,
};
#[test]
fn can_remove_node() {
let mut genome = Genome {
inputs: Genes(vec![Node::input(Id(0), 0)].iter().cloned().collect()),
hidden: Genes(
vec![
Node::hidden(Id(2), Activation::Linear),
Node::hidden(Id(3), Activation::Linear),
]
.iter()
.cloned()
.collect(),
),
outputs: Genes(
vec![Node::output(Id(1), 0, Activation::Linear)]
.iter()
.cloned()
.collect(),
),
feed_forward: Genes(
vec![
Connection::new(Id(0), 1.0, Id(2)),
Connection::new(Id(0), 1.0, Id(3)),
Connection::new(Id(2), 1.0, Id(1)),
Connection::new(Id(3), 1.0, Id(1)),
]
.iter()
.cloned()
.collect(),
),
..Default::default()
};
assert!(Mutations::remove_node(&mut genome, &mut thread_rng()).is_ok())
}
#[test]
fn can_not_remove_node() {
let mut genome = Genome {
inputs: Genes(vec![Node::input(Id(0), 0)].iter().cloned().collect()),
hidden: Genes(
vec![Node::hidden(Id(2), Activation::Linear)]
.iter()
.cloned()
.collect(),
),
outputs: Genes(
vec![Node::output(Id(1), 0, Activation::Linear)]
.iter()
.cloned()
.collect(),
),
feed_forward: Genes(
vec![
Connection::new(Id(0), 1.0, Id(2)),
Connection::new(Id(2), 1.0, Id(1)),
]
.iter()
.cloned()
.collect(),
),
..Default::default()
};
if let Err(error) = Mutations::remove_node(&mut genome, &mut thread_rng()) {
assert_eq!(error, MutationError::CouldNotRemoveNode);
} else {
unreachable!()
}
}
}