From 6aae1f6fb4cf289ecf5ed318b34c0e7df62bbf83 Mon Sep 17 00:00:00 2001
From: sanine-a <sanine.not@pm.me>
Date: Tue, 1 Aug 2023 17:03:28 -0500
Subject: add mutation_type and mutate()

---
 src/genome/genome.js      | 49 +++++++++++++++++++++++++++++++++++++++++++++++
 src/genome/genome.test.js | 20 +++++++++++++++++++
 2 files changed, 69 insertions(+)
 create mode 100644 src/genome/genome.js
 create mode 100644 src/genome/genome.test.js

(limited to 'src/genome')

diff --git a/src/genome/genome.js b/src/genome/genome.js
new file mode 100644
index 0000000..16de162
--- /dev/null
+++ b/src/genome/genome.js
@@ -0,0 +1,49 @@
+'use strict';
+
+
+export const mutation_type = Object.freeze({
+  none: 'none',
+  source: 'source',
+  sink: 'sink',
+  weight: 'weight',
+});
+
+
+function positive(x) {
+  if (x < 0) { 
+    return 0; 
+  } else {
+    return x;
+  }
+}
+
+
+export function mutate(gene, type, value) {
+  const [ source, sink, weight ] = gene;
+
+  switch(type) {
+    case mutation_type.none:
+      return [...gene];
+
+    case mutation_type.source:
+      if (value <= 0.5) {
+        return [ positive(source-1), sink, weight ];
+      } else {
+        return [ source+1, sink, weight ];
+      }
+
+    case mutation_type.sink:
+      if (value <= 0.5) {
+        return [ source, positive(sink-1), weight ];
+      } else {
+        return [ source, sink+1, weight ];
+      }
+
+    case mutation_type.weight:
+      const w = (8*value) - 4;
+      return [ source, sink, w ];
+
+    default:
+      throw new Error(`unknown mutation type: '${type}'`);
+  };
+}
diff --git a/src/genome/genome.test.js b/src/genome/genome.test.js
new file mode 100644
index 0000000..853d103
--- /dev/null
+++ b/src/genome/genome.test.js
@@ -0,0 +1,20 @@
+'use strict';
+
+import { mutation_type, mutate } from './genome';
+
+
+test('basic gene mutations', () => {
+  expect(mutate([0, 1, 2], mutation_type.none, 0)).toEqual([0, 1, 2]);
+
+  expect(mutate([0, 1, 2], mutation_type.source, 0.2)).toEqual([0, 1, 2]);
+  expect(mutate([1, 1, 2], mutation_type.source, 0.2)).toEqual([0, 1, 2]);
+  expect(mutate([0, 1, 2], mutation_type.source, 0.8)).toEqual([1, 1, 2]);
+
+  expect(mutate([0, 1, 2], mutation_type.sink, 0.2)).toEqual([0, 0, 2]);
+  expect(mutate([0, 1, 2], mutation_type.sink, 0.8)).toEqual([0, 2, 2]);
+  expect(mutate([0, 0, 2], mutation_type.sink, 0.2)).toEqual([0, 0, 2]);
+
+  expect(mutate([0, 1, 2], mutation_type.weight, 0.5)).toEqual([0, 1, 0]);
+  expect(mutate([0, 1, 2], mutation_type.weight, 0.0)).toEqual([0, 1, -4]);
+  expect(mutate([0, 1, 2], mutation_type.weight, 1.0)).toEqual([0, 1, 4]);
+});
-- 
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