path: root/src/genome/genome.js

'use strict';

import { random_choice } from '../util.js';
import { network } from '../mind/topology.js';


// check if a given genome is valid and compute its size
export function get_size(num_input, num_output, genome) {
  const [ max_index, max_weight ] = genome.reduce(
    ([max_index, max_weight ], [ source, sink, weight]) => [
      Math.max(max_index, source, sink),
      Math.max(max_weight, Math.abs(weight)),
    ],
    [ 0, 0 ]
  );

  if (max_index < num_input + num_output - 1) {
    return -1;
  }
  else if (max_weight > 4.0) {
    return -1;
  }
  else {
    return max_index + 1;
  }
}


// parse a genome into a useable neural net
export function parse_genome(num_input, num_output, genome) {
  const size = get_size(num_input, num_output, genome);
  if (size < 0) {
    // bad genome
    throw new Error('invalid genome sequence!');
  }

  const n = genome.reduce(
    (acc, [source, sink, weight]) => acc.connect(source, sink, weight),
    network(num_input, size-num_input-num_output, num_output)
  );

  return n;
}


// --===== mutations =====--

function clamp(value, min, max) {
  if (value > max) { return max; }
  if (value < min) { return min; }
  return value;
}

// adjust the source input of a gene
export function mut_gene_source(n_input, n_internal, n_output, gene, r) {
  const [source, sink, weight] = gene;

  const new_source = r < 0.5 ? source-1 : source+1;

  return [
    clamp(new_source, 0, n_input+n_internal-1), 
    sink, 
    weight,
  ];
}


// adjust the sink target of a gene
export function mut_gene_sink(n_input, n_internal, n_output, gene, r) {
  const [source, sink, weight] = gene;

  const new_sink = r < 0.5 ? sink-1 : sink+1;

  return [
    source, 
    clamp(new_sink,  n_input+n_internal, n_input+n_internal+n_output-1), 
    weight,
  ];
}


// modify a gene's weight
// only adjusts the weight by performing a weighted average, so as to
// more gently modify the generated net
export function mut_gene_weight(weight_max, gene, r) {
  const [source, sink, weight] = gene;
  
  const rr = (2*r)-1;
  const move = weight_max * rr;
  const new_weight = (2*weight + move)/3;

  return [
    source,
    sink,
    clamp(new_weight, -weight_max, weight_max),
  ];
}



// expand the size of the neural net encoded by the genome
// relabels internal indices so that there is one extra internal neuron
export function mut_genome_expand(
  [n_input, n_internal, n_output, genome], r
) {
  const expand_index = Math.floor(n_internal * r) + n_input;
  const new_genome = genome.map(([source, sink, weight]) => [
    source >= expand_index ? source+1 : source,
    sink >= expand_index ? sink+1 : sink,
    weight,
  ]);

  return [
    n_input, n_internal+1, n_output, new_genome,
  ];
}


// contract the size of the neural net encoded by the genome
// relabels internal indices so that there is one less internal neuron
export function mut_genome_contract(
  [n_input, n_internal, n_output, genome], r
) {
  const contract_idx = Math.floor(n_internal * r) + n_input;

  // decrement sources on the contract index too, to prevent invalid genomes
  const new_source = (source) => source >= contract_idx ? source-1 : source;
  // decrement sinks only after the contract index
  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
  ];
}


// append a newly generated gene to the end of the genome
export function mut_genome_insert(
  [n_input, n_internal, n_output, genome], 
  weight_max, 
  r1, r2, r3
) {
  const source = Math.floor((n_input + n_internal) * r1);
  const sink   = Math.floor((n_internal + n_output) * r2) + n_input;
  const weight = weight_max * ((2*r3)-1);

  return [
    n_input, n_internal, n_output,
    [...genome, [source, sink, weight]],
  ];
}


// delete a gene from the genome
export function mut_genome_delete(
  [n_input, n_internal, n_output, genome], r
) {
  const del_idx = Math.floor(r * genome.length);
  const new_genome = genome.filter((_, idx) => idx != del_idx);
  return [n_input, n_internal, n_output, new_genome];
}


function mut_gene(
  [n_input, n_internal, n_output, genome], 
  weight_max, r1, r2, r3
) {
  const gene_idx = Math.floor(genome.length * r1);
  const mod = random_choice(['source', 'sink', 'weight'], r2);
  let new_gene;
  if (mod == 'source') {
    new_gene = mut_gene_source(
      n_input, n_internal, n_output, 
      genome[gene_idx],
      r3
    );
  } else if (mod == 'sink') {
    new_gene = mut_gene_sink(
      n_input, n_internal, n_output, 
      genome[gene_idx],
      r3
    );
  } else {
    new_gene = mut_gene_weight(
      weight_max, genome[gene_idx], r3
    );
  }

  const new_genome = genome.map((gene, idx) => {
    if (idx == gene_idx) { return new_gene; }
    return gene;
  });

  return [
    n_input, n_internal, n_output, new_genome
  ];
}


export function mutate_genome(obj, weight_max) {
  const mut = random_choice([
    'gene', 'gene', 'gene',
    'gene', 'gene', 'gene',
    'gene', 'gene', 'gene',
    'insert', 'delete',
    'insert', 'delete',
    'expand', 'contract',
  ], Math.random());

  if (mut == 'gene') {
    return mut_gene(
      obj, weight_max, 
      Math.random(), Math.random(), Math.random()
    );
  } else if (mut == 'insert') {
    return mut_genome_insert(
      obj, weight_max, 
      Math.random(), Math.random(), Math.random()
    );
  } else if (mut == 'delete') {
    return mut_genome_delete(obj, Math.random());
  } else if (mut == 'expand') {
    return mut_genome_expand(obj, Math.random());
  } else if (mut == 'contract') {
    return mut_genome_contract(obj, Math.random());
  } else {
    throw new Error(`bad mut value: ${mut}`);
  }
}