use average weight in mutation and add README.md

3 files changed, 16 insertions, 4 deletions

diff --git a/src/genome/README.md b/src/genome/README.md
new file mode 100644
index 0000000..1135ed0
--- /dev/null
+++ b/src/genome/README.md
@@ -0,0 +1,12 @@
+src/genome

+==========

+

+Genomes represent the neural network that underlies a creature. They are an array of tuples of the form `[ source, sink, weight ]`, where:

+

+  * `source` is an integer in the range `[0, N - num_outputs)`, representing the index of the source neuron

+  * `sink` is an integer in the range `[num_inputs, N)`, representing the index of the sink neuron

+  * `weight` is a floating-point value in the range `[-4, 4]`, representing the weight of the connection

+

+`num_input` and `num_output` are fixed by the environment (as they are the input senses and output actions of the creature, respectively). 

+`N` is not fixed, but is instead determined by the maximum index present in the genome. As long as the maximum index is greater than or 

+equal to `num_input + num_output`, the genome is considered valid.

diff --git a/src/genome/genome.js b/src/genome/genome.js
index 8e0c9f0..e2bf83e 100644
--- a/src/genome/genome.js
+++ b/src/genome/genome.js
@@ -41,7 +41,7 @@ export function mutate(gene, type, value) {
 

     case mutation_type.weight:

       const w = (8*value) - 4;

-      return [ source, sink, w ];

+      return [ source, sink, 0.5*(w + weight) ];

 

     default:

       throw new Error(`unknown mutation type: '${type}'`);

diff --git a/src/genome/genome.test.js b/src/genome/genome.test.js
index 853d103..ca56092 100644
--- a/src/genome/genome.test.js
+++ b/src/genome/genome.test.js
@@ -14,7 +14,7 @@ test('basic gene mutations', () => {
   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]);

+  expect(mutate([0, 1, 2], mutation_type.weight, 0.5)).toEqual([0, 1, 1]);

+  expect(mutate([0, 1, 2], mutation_type.weight, 0.0)).toEqual([0, 1, -1]);

+  expect(mutate([0, 1, 2], mutation_type.weight, 1.0)).toEqual([0, 1, 3]);

 });