2 files changed, 71 insertions, 0 deletions
diff --git a/src/genome/genome.js b/src/genome/genome.js
index 16b5e4d..d2650b5 100644
--- a/src/genome/genome.js
+++ b/src/genome/genome.js
@@ -106,6 +106,25 @@ export function mut_genome_expand(
 }
 
 
+export function mut_genome_contract(
+  [n_input, n_internal, n_output, genome], r
+) {
+  const contract_idx = Math.floor(n_internal * r) + n_input;
+  const new_source = (source) => source >= contract_idx ? source-1 : source;
+  const new_sink   = (sink)   => sink > contract_idx ? sink-1 : sink;
+
+  const new_genome = genome.map(([source, sink, weight]) => [
+    new_source(source), 
+    new_sink(sink), 
+    weight,
+  ]);
+
+  return [
+    n_input, n_internal-1, n_output, new_genome
+  ];
+}
+
+
 export function mut_genome_insert(
   [n_input, n_internal, n_output, genome], 
   weight_max, 
diff --git a/src/genome/genome.test.js b/src/genome/genome.test.js
index a021073..37bdacc 100644
--- a/src/genome/genome.test.js
+++ b/src/genome/genome.test.js
@@ -7,6 +7,7 @@ import {
   mut_gene_sink,
   mut_gene_weight,
   mut_genome_expand,
+  mut_genome_contract,
   mut_genome_insert,
   mut_genome_delete,
 } from './genome';
@@ -165,6 +166,57 @@ test('expand genome', () => {
 });
 
 
+test('contract genome', () => {
+  const n_input = 1;
+  const n_internal = 3;
+  const n_output = 1;
+
+  const genome = [
+    [0, 1, 0],
+    [1, 2, 1],
+    [2, 3, 2],
+    [3, 4, 3],
+  ];
+
+  expect(mut_genome_contract([
+    n_input, n_internal, n_output, genome
+  ], 0.0)).toEqual([
+    n_input, n_internal-1, n_output,
+    [
+      [0, 1, 0],
+      [0, 1, 1],
+      [1, 2, 2],
+      [2, 3, 3],
+    ],
+  ]);
+
+  expect(mut_genome_contract([
+    n_input, n_internal, n_output, genome
+  ], 0.5)).toEqual([
+    n_input, n_internal-1, n_output,
+    [
+      [0, 1, 0],
+      [1, 2, 1],
+      [1, 2, 2],
+      [2, 3, 3],
+    ],
+  ]);
+
+  expect(mut_genome_contract([
+    n_input, n_internal, n_output, genome
+  ], 0.99)).toEqual([
+    n_input, n_internal-1, n_output,
+    [
+      [0, 1, 0],
+      [1, 2, 1],
+      [2, 3, 2],
+      [2, 3, 3],
+    ],
+  ]);
+});
+
+
+
 test('insert new genes', () => {
   const n_input = 1;
   const n_internal = 2;