remove 50/50 direction approach for pre-clamped Range bandwidth

mutations, as it oversampled the direction with the smaller range. Now
uniformly sample over complete pre-clamped bandwidth, without
directionallity concerns

Author: basvanwesting

README.md

@@ -188,16 +188,6 @@ Run with `cargo run --example profile_evolve_binary --release -- --bench --profi
 Find the flamegraph in: `./target/criterion/profile_evolve_binary/profile/flamegraph.svg`
 
 ## TODO
-* There is an issue with MutationType::RangeScaled. The pre-clamping solves the
-  issue of oversampling the borders when using a large intermediate bandwidth.
-  But it doesn't solve the 50/50 probability of sampling up or down. If the
-  gene is nearer to an edge, the effective bandwidth is smaller due to
-  pre-clamping, but that oversamples the bandwidth with regard to the other
-  direction's bandwidth size. This effect gets stronger nearer to the edge. 50%
-  of the samples fall between the current value and the edge, which feels very
-  unbalanced. Need to sample the whole pre-clamped bandwidth as a whole (how to
-  do that for unsigned int?) or need to balance the probability by bandwidth
-  size
 
 ## MAYBE
 * Apply precision (to f32/f64) during hashing in order to converge and hit

src/genotype/multi_range.rs

@@ -309,23 +309,14 @@ where
                     } else {
                         // Bandwidth
                         let current_value = chromosome.genes[index];
-                        if rng.gen() {
-                            let max_delta_up = allele_range_end - current_value;
-                            let working_delta_up = T::min(bandwidth, max_delta_up);
-                            if working_delta_up >= T::smallest_increment() {
-                                let delta =
-                                    rng.gen_range(T::smallest_increment()..=working_delta_up);
-                                chromosome.genes[index] += delta; // no need to check again
-                            }
-                        } else {
-                            let max_delta_down = current_value - allele_range_start;
-                            let working_delta_down = T::min(bandwidth, max_delta_down);
-                            if working_delta_down >= T::smallest_increment() {
-                                let delta =
-                                    rng.gen_range(T::smallest_increment()..=working_delta_down);
-                                chromosome.genes[index] -= delta; // no need to check again
-                            }
-                        }
+                        let max_delta_up = allele_range_end - current_value;
+                        let max_delta_down = current_value - allele_range_start;
+                        let working_delta_up = T::min(bandwidth, max_delta_up);
+                        let working_delta_down = T::min(bandwidth, max_delta_down);
+                        let working_range_end = current_value + working_delta_up;
+                        let working_range_start = current_value - working_delta_down;
+                        chromosome.genes[index] =
+                            rng.gen_range(working_range_start..=working_range_end);
                     }
                 }
             }

src/genotype/mutation_type.rs

@@ -93,7 +93,7 @@ use crate::allele::Allele;
 ///
 /// **Behavior by phase:**
 /// - Phase 0: Mutations uniformly within full allele range (same as Random, pre-clamped)
-/// - Phase 1: Mutations uniformly within full allele range (extended round, more exploration)
+/// - Phase 1: Mutations uniformly within full allele range (another Random round)
 /// - Phase 2: Mutations uniformly within ±50 (pre-clamped)
 /// - Phase 3: Mutations uniformly within ±20 (pre-clamped)
 /// - Phase 4: Mutations uniformly within ±5 (pre-clamped)
@@ -187,14 +187,16 @@ use crate::allele::Allele;
 ///
 /// ## Boundary Sampling Summary
 ///
-/// - `Random`: Undersamples boundaries (infinitesimal probability)
-/// - `Range`: Post-clamped, slight boundary oversampling when near edges
-/// - `Step`: Always clamped, slight boundary oversampling when near edges
-/// - `RangeScaled`:
-///   - Non-final phases: Pre-clamped, boundaries undersampled
-///   - Final phase: Post-clamped, slight boundary oversampling
-/// - `StepScaled`: Always clamped, slight boundary oversampling
-/// - `Discrete`: Uniform sampling, no boundary bias
+/// * `Random`: Undersamples boundaries (infinitesimal probability)
+/// * `Range`: Post-clamped, slight boundary oversampling when near edges (assuming small bandwidth)
+/// * `Step`: Always clamped, slight boundary oversampling when near edges (assuming small step)
+/// * `RangeScaled`:
+///   * Non-final phases: Pre-clamped, boundaries undersampled
+///   * Final phase: Post-clamped, slight boundary oversampling (assuming small final bandwidth)
+/// * `StepScaled`: Always clamped
+///   * First phase: Given potentially large step in the first phase, the boundary can become quite oversampled
+///   * Non-first phases: slight boundary oversampling (assuming small steps)
+/// * `Discrete`: Uniform sampling, no boundary bias
 ///
 /// # Phase Management
 ///

src/genotype/range.rs

@@ -216,23 +216,14 @@ where
                     } else {
                         // Bandwidth
                         let current_value = chromosome.genes[index];
-                        if rng.gen() {
-                            let max_delta_up = allele_range_end - current_value;
-                            let working_delta_up = T::min(bandwidth, max_delta_up);
-                            if working_delta_up >= T::smallest_increment() {
-                                let delta =
-                                    rng.gen_range(T::smallest_increment()..=working_delta_up);
-                                chromosome.genes[index] += delta; // no need to check again
-                            }
-                        } else {
-                            let max_delta_down = current_value - allele_range_start;
-                            let working_delta_down = T::min(bandwidth, max_delta_down);
-                            if working_delta_down >= T::smallest_increment() {
-                                let delta =
-                                    rng.gen_range(T::smallest_increment()..=working_delta_down);
-                                chromosome.genes[index] -= delta; // no need to check again
-                            }
-                        }
+                        let max_delta_up = allele_range_end - current_value;
+                        let max_delta_down = current_value - allele_range_start;
+                        let working_delta_up = T::min(bandwidth, max_delta_up);
+                        let working_delta_down = T::min(bandwidth, max_delta_down);
+                        let working_range_end = current_value + working_delta_up;
+                        let working_range_start = current_value - working_delta_down;
+                        chromosome.genes[index] =
+                            rng.gen_range(working_range_start..=working_range_end);
                     }
                 }
             }

tests/genotype/multi_range_test.rs

@@ -114,7 +114,7 @@ fn float_mutate_chromosome_single_range_scaled() {
     genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.447, 1.219, 15.704],
+        vec![0.447, 2.833, 16.854],
         0.001
     ));
 
@@ -123,7 +123,7 @@ fn float_mutate_chromosome_single_range_scaled() {
     genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.417, 1.331, 15.704],
+        vec![0.392, 2.833, 17.697],
         0.001
     ));
 
@@ -132,7 +132,7 @@ fn float_mutate_chromosome_single_range_scaled() {
     genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.417, 1.288, 15.685],
+        vec![0.399, 2.833, 17.678],
         0.001
     ));
 }

tests/genotype/range_test.rs

@@ -96,35 +96,34 @@ fn float_mutate_chromosome_single_range_scaled() {
     ));
 
     assert_eq!(genotype.current_scale_index, 0);
-    genotype.mutate_chromosome_genes(1, true, &mut chromosome, &mut rng);
+    genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.447, 0.897, 0.979],
+        vec![0.447, 0.818, 0.395],
         0.001,
     ));
 
     assert!(genotype.increment_scale_index());
     assert_eq!(genotype.current_scale_index, 1);
-    genotype.mutate_chromosome_genes(1, true, &mut chromosome, &mut rng);
-    genotype.mutate_chromosome_genes(1, true, &mut chromosome, &mut rng);
+    genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.447, 0.921, 0.989],
+        vec![0.392, 0.818, 0.479],
         0.001,
     ));
 
     assert!(genotype.increment_scale_index());
     assert_eq!(genotype.current_scale_index, 2);
-    genotype.mutate_chromosome_genes(1, true, &mut chromosome, &mut rng);
+    genotype.mutate_chromosome_genes(2, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.447, 0.921, 0.982],
+        vec![0.399, 0.818, 0.477],
         0.001,
     ));
 }
 
 #[test]
-fn float_mutate_chromosome_single_range_scaled_on_edge() {
+fn float_mutate_chromosome_single_range_scaled_on_edge_and_zero_bandwidth() {
     let mut rng = SmallRng::seed_from_u64(1);
     let mut genotype = RangeGenotype::builder()
         .with_genes_size(3)
@@ -140,7 +139,7 @@ fn float_mutate_chromosome_single_range_scaled_on_edge() {
     genotype.mutate_chromosome_genes(3, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.970, 0.0, 0.904],
+        vec![0.911, 0.095, 0.947],
         0.001,
     ));
 
@@ -149,7 +148,7 @@ fn float_mutate_chromosome_single_range_scaled_on_edge() {
     genotype.mutate_chromosome_genes(3, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.970, 0.0, 0.904],
+        vec![0.911, 0.095, 0.947],
         0.001,
     ));
 
@@ -158,7 +157,7 @@ fn float_mutate_chromosome_single_range_scaled_on_edge() {
     genotype.mutate_chromosome_genes(3, false, &mut chromosome, &mut rng);
     assert!(relative_chromosome_eq(
         inspect::chromosome(&chromosome),
-        vec![0.970, 0.0, 0.904],
+        vec![0.911, 0.095, 0.947],
         0.001,
     ));
 }