feat: added a Drift trait and a "default" ConstantDrift implementation

src/batch.rs

@@ -1,7 +1,8 @@
 use std::collections::HashMap;
 
 use crate::{
-    agent::Agent, game::Game, gaussian::Gaussian, player::Player, tuple_gt, tuple_max, Index, N_INF,
+    Index, N_INF, agent::Agent, drift::Drift, game::Game, gaussian::Gaussian, player::Player,
+    tuple_gt, tuple_max,
 };
 
 #[derive(Debug)]
@@ -38,22 +39,22 @@ struct Item {
 }
 
 impl Item {
-    fn within_prior(
+    fn within_prior<D: Drift>(
         &self,
         online: bool,
         forward: bool,
         skills: &HashMap<Index, Skill>,
-        agents: &HashMap<Index, Agent>,
-    ) -> Player {
+        agents: &HashMap<Index, Agent<D>>,
+    ) -> Player<D> {
         let r = &agents[&self.agent].player;
         let skill = &skills[&self.agent];
 
         if online {
-            Player::new(skill.online, r.beta, r.gamma)
+            Player::new(skill.online, r.beta, r.drift)
         } else if forward {
-            Player::new(skill.forward, r.beta, r.gamma)
+            Player::new(skill.forward, r.beta, r.drift)
         } else {
-            Player::new(skill.posterior() / self.likelihood, r.beta, r.gamma)
+            Player::new(skill.posterior() / self.likelihood, r.beta, r.drift)
         }
     }
 }
@@ -79,13 +80,13 @@ impl Event {
             .collect::<Vec<_>>()
     }
 
-    pub(crate) fn within_priors(
+    pub(crate) fn within_priors<D: Drift>(
         &self,
         online: bool,
         forward: bool,
         skills: &HashMap<Index, Skill>,
-        agents: &HashMap<Index, Agent>,
-    ) -> Vec<Vec<Player>> {
+        agents: &HashMap<Index, Agent<D>>,
+    ) -> Vec<Vec<Player<D>>> {
         self.teams
             .iter()
             .map(|team| {
@@ -116,12 +117,12 @@ impl Batch {
         }
     }
 
-    pub fn add_events(
+    pub fn add_events<D: Drift>(
         &mut self,
         composition: Vec<Vec<Vec<Index>>>,
         results: Vec<Vec<f64>>,
         weights: Vec<Vec<Vec<f64>>>,
-        agents: &HashMap<Index, Agent>,
+        agents: &HashMap<Index, Agent<D>>,
     ) {
         let mut unique = Vec::with_capacity(10);
 
@@ -207,7 +208,7 @@ impl Batch {
             .collect::<HashMap<_, _>>()
     }
 
-    pub fn iteration(&mut self, from: usize, agents: &HashMap<Index, Agent>) {
+    pub fn iteration<D: Drift>(&mut self, from: usize, agents: &HashMap<Index, Agent<D>>) {
         for event in self.events.iter_mut().skip(from) {
             let teams = event.within_priors(false, false, &self.skills, agents);
             let result = event.outputs();
@@ -229,7 +230,7 @@ impl Batch {
     }
 
     #[allow(dead_code)]
-    pub(crate) fn convergence(&mut self, agents: &HashMap<Index, Agent>) -> usize {
+    pub(crate) fn convergence<D: Drift>(&mut self, agents: &HashMap<Index, Agent<D>>) -> usize {
         let epsilon = 1e-6;
         let iterations = 20;
 
@@ -259,18 +260,18 @@ impl Batch {
         skill.forward * skill.likelihood
     }
 
-    pub(crate) fn backward_prior_out(
+    pub(crate) fn backward_prior_out<D: Drift>(
         &self,
         agent: &Index,
-        agents: &HashMap<Index, Agent>,
+        agents: &HashMap<Index, Agent<D>>,
     ) -> Gaussian {
         let skill = &self.skills[agent];
         let n = skill.likelihood * skill.backward;
 
-        n.forget(agents[agent].player.gamma, skill.elapsed)
+        n.forget(agents[agent].player.drift.variance_delta(skill.elapsed))
     }
 
-    pub(crate) fn new_backward_info(&mut self, agents: &HashMap<Index, Agent>) {
+    pub(crate) fn new_backward_info<D: Drift>(&mut self, agents: &HashMap<Index, Agent<D>>) {
         for (agent, skill) in self.skills.iter_mut() {
             skill.backward = agents[agent].message;
         }
@@ -278,7 +279,7 @@ impl Batch {
         self.iteration(0, agents);
     }
 
-    pub(crate) fn new_forward_info(&mut self, agents: &HashMap<Index, Agent>) {
+    pub(crate) fn new_forward_info<D: Drift>(&mut self, agents: &HashMap<Index, Agent<D>>) {
         for (agent, skill) in self.skills.iter_mut() {
             skill.forward = agents[agent].receive(skill.elapsed);
         }
@@ -286,12 +287,12 @@ impl Batch {
         self.iteration(0, agents);
     }
 
-    pub(crate) fn log_evidence(
+    pub(crate) fn log_evidence<D: Drift>(
         &self,
         online: bool,
         targets: &[Index],
         forward: bool,
-        agents: &HashMap<Index, Agent>,
+        agents: &HashMap<Index, Agent<D>>,
     ) -> f64 {
         if targets.is_empty() {
             if online || forward {
@@ -390,7 +391,7 @@ pub(crate) fn compute_elapsed(last_time: i64, actual_time: i64) -> i64 {
 mod tests {
     use approx::assert_ulps_eq;
 
-    use crate::{agent::Agent, player::Player, IndexMap};
+    use crate::{IndexMap, agent::Agent, drift::ConstantDrift, player::Player};
 
     use super::*;
 
@@ -414,7 +415,7 @@ mod tests {
                     player: Player::new(
                         Gaussian::from_ms(25.0, 25.0 / 3.0),
                         25.0 / 6.0,
-                        25.0 / 300.0,
+                        ConstantDrift(25.0 / 300.0),
                     ),
                     ..Default::default()
                 },
@@ -490,7 +491,7 @@ mod tests {
                     player: Player::new(
                         Gaussian::from_ms(25.0, 25.0 / 3.0),
                         25.0 / 6.0,
-                        25.0 / 300.0,
+                        ConstantDrift(25.0 / 300.0),
                     ),
                     ..Default::default()
                 },
@@ -569,7 +570,7 @@ mod tests {
                     player: Player::new(
                         Gaussian::from_ms(25.0, 25.0 / 3.0),
                         25.0 / 6.0,
-                        25.0 / 300.0,
+                        ConstantDrift(25.0 / 300.0),
                     ),
                     ..Default::default()
                 },