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use crate::colony::Colony;
use crate::cycle::brent_cycle;
use crate::petgraph::graph::NodeIndex;
use crate::petgraph::EdgeType;
use crate::Objective;
use rand::distributions::{Distribution, Uniform};
use rand::rngs::SmallRng;
use rand::{Rng, SeedableRng};
use std::cmp::PartialEq;
use std::fmt::{Debug, Display};
use std::marker::Send;
#[derive(Debug)]
pub struct Ant {
pub number: usize,
pub visited_nodes: Vec<usize>,
pub visited_edges: Vec<usize>,
pub edge_weight: f64,
obj: Objective,
rng: SmallRng,
cycling: bool,
}
impl Ant {
pub fn from_node(number: usize, node_idx: usize, seed: u64, obj: Objective) -> Ant {
Ant {
number,
visited_nodes: vec![node_idx],
visited_edges: Vec::new(),
edge_weight: 0.0,
obj,
rng: SmallRng::seed_from_u64(seed),
cycling: false,
}
}
pub fn move_prob<
N: 'static + Clone + Display + Debug + PartialEq + Send,
Ty: 'static + Clone + EdgeType + Send,
>(
&self,
colony: &Colony<N, Ty>,
from: usize,
to: usize,
) -> f64 {
let numerator = colony.unnormalized_probability(from, to);
let mut denominator = 0.0;
let neighbors = colony.pheromone_graph.neighbors(NodeIndex::new(from));
// Compute the denominator from the neightboring nodes only
for nodeidx in neighbors {
if !self.visited_nodes.contains(&nodeidx.index()) || self.cycling {
denominator += colony.unnormalized_probability(from, nodeidx.index());
}
}
numerator / denominator
}
/// Moves an ant to the next node. Returns false when the objective is satisfied.
pub fn move_ant<
N: 'static + Clone + Display + Debug + PartialEq + Send,
Ty: 'static + Clone + EdgeType + Send,
>(
&mut self,
colony: &Colony<N, Ty>,
) -> bool {
match self.obj {
Objective::VisitAllNodes => {
if self.visited_nodes.len() == colony.pheromone_graph.node_count() {
// If we have a complete graph, then this condition exists
debug!("Ant#{} has visited all nodes", self.number);
return false;
}
}
Objective::VisitNNodes(n) => {
if self.visited_nodes.len() == n {
// If we have a complete graph, then this condition exists
debug!("Ant#{} has visited {} nodes", self.number, n);
return false;
}
}
Objective::ReachNodeIdx(idx) => {
if self.visited_nodes.contains(&idx) {
// If we have a complete graph, then this condition exists
debug!(
"Ant#{} has reached destination node {} (idx: {})",
self.number,
colony.viz_graph[NodeIndex::new(idx)],
idx
);
return false;
}
}
_ => {}
}
// Move to the next node which has the highest probability based on the connected nodes.
let current_node = *self.visited_nodes.last().unwrap();
let neighbors = colony
.pheromone_graph
.neighbors(NodeIndex::new(current_node));
let mut next_node = 0;
if self.rng.gen::<f64>() < colony.opt.wander {
// Take a random step regardless of the pheromones
// NOTE: We always need to choose from the neighbors instead of guessing the next node
// or we may try to create a link when there is none in an incomplete graph.
debug!("Ant#{} wandering", self.number);
// Let's check that there are some neighbors which have not been visited.
let num_neighbors = neighbors.clone().count();
let mut all_neighbors_visited = true;
let mut available_neighbors = Vec::new();
for neighbor in neighbors.clone() {
if !self.visited_nodes.contains(&neighbor.index()) {
all_neighbors_visited = false;
// And set the next node to this.
available_neighbors.push(neighbor);
}
}
if all_neighbors_visited {
match self.obj {
Objective::ReachDeadEnd => {
debug!(
"Ant#{} has hit a dead end after {} nodes",
self.number,
self.visited_nodes.len()
);
// Let's normalize the weight over the number of nodes
self.edge_weight /= self.visited_nodes.len() as f64;
return false;
}
_ => {
// If there are no neighbors, we're done for!
if neighbors.clone().count() == 0 {
warn!(
"Ant#{} has hit a dead end and there are no neighbors",
self.number,
);
return false;
}
// Return to the path with the highest pheromone trail
// Go to the node with the highest pheromone levels.
let mut max_prob = 0.0;
// Mark this ant as currently cycling to compute the probability all of
// nodes and not simply those which have not been visited.
self.cycling = true;
// Find neighboring nodes
for nodeidx in neighbors {
let next_prob = self.move_prob(&colony, current_node, nodeidx.index());
debug!(
"Ant#{} - {} -> {}: {}",
self.number,
colony.viz_graph[NodeIndex::new(current_node)],
colony.viz_graph[nodeidx],
next_prob
);
if next_prob > max_prob {
max_prob = next_prob;
next_node = nodeidx.index();
}
}
debug!(
"Ant#{} reached a dead end, going backward to {} with probability {}",
self.number,
colony.viz_graph[NodeIndex::new(next_node)],
max_prob
);
self.cycling = false; // Node selected, we're done cycling
}
}
} else {
// Randomly chose a neighbor from those available.
let next_node_idx =
Uniform::from(0..available_neighbors.len()).sample(&mut self.rng);
next_node = available_neighbors[next_node_idx].index();
debug!(
"randomly chose {} from {} neighbors, currently at {}",
colony.viz_graph[NodeIndex::new(next_node)],
num_neighbors,
colony.viz_graph[NodeIndex::new(current_node)]
);
}
} else {
// Go to the node with the highest pheromone levels.
let mut max_prob = 0.0;
let mut dead_end = true;
// Find neighboring nodes
for nodeidx in neighbors {
if self.visited_nodes.contains(&nodeidx.index()) {
continue; // No backtrack
}
dead_end = false;
let next_prob = self.move_prob(&colony, current_node, nodeidx.index());
debug!(
"Ant#{} - {} -> {}: {}",
self.number,
colony.viz_graph[NodeIndex::new(current_node)],
colony.viz_graph[nodeidx],
next_prob
);
if next_prob > max_prob {
max_prob = next_prob;
next_node = nodeidx.index();
}
}
if dead_end {
match self.obj {
Objective::ReachDeadEnd => {
debug!(
"Ant#{} has hit a dead end after {} nodes",
self.number,
self.visited_nodes.len()
);
// Let's normalize the weight over the number of nodes
self.edge_weight /= self.visited_nodes.len() as f64;
return false;
}
_ => {
// If we have an incomplete graph, then this condition exists
debug!("Ant#{} reached a dead end, going backward!", self.number);
next_node = self.visited_nodes[self.visited_nodes.len() - 2];
debug!(
"next node will be {} from {}",
colony.viz_graph[NodeIndex::new(next_node)],
colony.viz_graph[NodeIndex::new(current_node)]
);
}
}
}
}
// And move and store the edge used.
self.visited_nodes.push(next_node);
match colony
.pheromone_graph
.find_edge(NodeIndex::new(current_node), NodeIndex::new(next_node))
{
Some(edge_idx) => {
self.visited_edges.push(edge_idx.index());
self.edge_weight += colony.viz_graph[edge_idx];
debug!(
"Ant#{} moved to {:?} using edge {:?} {:?}",
self.number,
colony.viz_graph[NodeIndex::new(next_node)],
edge_idx,
edge_idx.index()
);
}
None => {
println!(
"Ant#{} cannot find edge from {} to {}!",
self.number, current_node, next_node
);
panic!("it broke");
}
}
// let edge_idx = colony
// .pheromone_graph
// .find_edge(NodeIndex::new(current_node), NodeIndex::new(next_node))
// .unwrap();
true
}
/// Remove any cycles and updates the cost function
pub fn remove_cycles<
N: 'static + Clone + Display + Debug + PartialEq + Send,
Ty: 'static + Clone + EdgeType + Send,
>(
&mut self,
colony: &Colony<N, Ty>,
) {
let new_nodes = brent_cycle(self.visited_nodes.as_slice());
if new_nodes.len() < self.visited_nodes.len() {
// Let's recompute the cost of those edges.
self.edge_weight = 0.0;
self.visited_edges = Vec::new();
let mut it = 0;
while it < new_nodes.len() - 1 {
debug!(
"getting edge between {} and {}",
new_nodes[it],
new_nodes[it + 1]
);
let edge_idx = colony
.pheromone_graph
.find_edge(
NodeIndex::new(new_nodes[it]),
NodeIndex::new(new_nodes[it + 1]),
)
.unwrap();
self.visited_edges.push(edge_idx.index());
self.edge_weight += colony.viz_graph[edge_idx];
it += 1;
}
self.visited_nodes = new_nodes;
}
}
}