Overfit neural network to find prime numbers

_prime_nn.rb

def is_prime?(n)
  bits = 8.times.map { |i| n[i] }
  [[[-8.8,  3.0,  9.2,  5.0, -4.8,  5.6, -5.8,  6.1, -6.1],
    [-1.8,  2.3, -2.6, -5.6,  0.1,  6.0, -4.7, -5.7, -3.0],
    [-3.6, -4.1,  6.5, -0.6, -2.8, -2.6,  2.4, -2.3,  1.0],
    [ 2.4, -9.1, -3.1,  7.8, -3.7, -8.9, -2.8,  5.6,  6.3],
    [-2.0,  4.0, 11.0,  3.3, -6.0,  0.7, -7.0,  1.6, -3.0],
    [ 0.7, -7.2,  2.8,  4.5, -3.6, -1.5,  2.7, -0.1, -3.5],
    [-8.9,  5.5,  4.8, -4.1,  5.6,  4.8,  5.5, -4.0, -6.4],
    [-4.0, -6.7, -3.6,  5.5,  2.5, -6.9,  7.8, -4.1, -0.4],
    [ 1.1, -3.5, -6.7, -2.8,  2.3, -4.7,  6.3, -4.6, -2.2]
   ],
   [[-14.6, -13.9, -9.4, -10.8, 13.7, 10.6, -10.7, -11.0, 12.7,  5.2]],
  ]
  .inject(bits) { |nodes_lhs, synapseses_rhs_major|
    synapseses_rhs_major.map { |synapses|
      total_input = [*nodes_lhs, 1.0].zip(synapses).map { |n, s| n*s }.inject(0, :+)
      1 / (1 + Math::E ** -total_input) # https://en.wikipedia.org/wiki/Sigmoid_function
    }
  }.first > 0.5
end

require 'prime'
(256).times.all? { |n| is_prime?(n) == Prime.prime?(n) } # => true

discoverer.rb

require 'ai4r/neural_network/backpropagation'
require 'prime'
# srand 1

def bits_for(n)
  [n[0],n[1],n[2],n[3],n[4],n[5],n[6],n[7]]
end

def train(net, n)
  net.train bits_for(n), [n.prime? ? 1 : 0]
end

loop do
  puts "Training the network, please wait.";
  max = (2**8)-1

  net = Ai4r::NeuralNetwork::Backpropagation.new([8, 9, 1]);

  2001.times do |i|
    errors = 0.upto(max).to_a.shuffle.map { |n| [n, train(net, n)] }
    next unless i % 200 == 0
    average = errors.map(&:last).inject(:+) / errors.length
    puts "Error for run #{i}: #{average.inspect}"
    next if i < 600
    # retrain = errors.select { |n, err| err > 0.2 }
    retrain = 0.upto(max).reject { |n| (0.5 < net.eval(bits_for n).first) == n.prime? }
    puts "  retraining on #{retrain.inspect}"
    500.times { retrain.each { |n| train net, n } }
  end

  puts "Test data"
  num_correct   = 0
  num_attempted = 0
  0.upto max do |n|
    num_attempted += 1
    result   = net.eval(bits_for n).first
    actual   = (0.5 <= result)
    expected = n.prime?
    (expected == actual) ? (num_correct += 1) : printf("%3d \e[31mreal:%-5s ai:%-5s\e[0m (%f)\n", n, expected, actual, result)
  end

  puts
  puts "SUMMARY: #{num_correct}/#{num_attempted} (#{100.0*num_correct/num_attempted}%)"
  if num_attempted == num_correct
    require "pry"
    binding.pry
  end
  puts "-----------------------------"
end

other_results.rb

# require 'pp'
# puts '[' << synapseses_rhs_major.map { |s| s.map { |s| '%4.1f' % s }.join(', ') }.join("],\n")

# 8 bits
# bits = [n[0], n[1], n[2], n[3], n[4], n[5], n[6], n[7]]
# [[[-3.2,  3.6, -0.7,  2.8,  0.9,  3.2, -0.1,  0.4, -2.3],
#   [-0.2, -3.0,  0.9, -3.8,  1.3,  3.1,  1.0, -2.4,  0.2],
#   [-1.0,  1.4, -0.0, -3.5,  1.6,  2.4, -2.9,  4.0, -1.0],
#   [-0.6,  3.0,  1.9,  2.4,  0.4,  0.4,  2.7,  0.6, -0.9],
#   [-4.1, -1.6,  2.8, -1.6,  0.6, -1.3,  3.3,  1.2, -0.5],
#   [ 0.0,  3.8, -5.0,  4.1, -5.2, -1.1, -5.9,  4.6,  1.3],
#   [-0.2,  2.0, -1.9, -1.0, -2.5,  6.2, -2.6, -0.3, -1.3],
#   [-0.3, -0.7,  0.6, -0.8,  1.3, -0.6,  1.9, -2.2, -0.2],
#   [-2.3, -0.3,  3.4, -2.6,  2.6, -1.2,  2.5, -2.1, -3.2],
#   [ 0.8, -0.9, -4.4,  3.4, -1.6,  2.5, -0.6, -2.1, -0.9],
#   [ 3.2,  3.7,  1.6, -3.8, -1.7,  4.5, -4.6,  3.2, -0.3],
#   [-0.3,  0.7,  1.1, -0.3, -0.8, -0.5, -0.3, -0.8, -0.4],
#   [-1.5,  1.7, -2.5,  0.3, -1.3,  2.0, -2.5,  0.4,  0.3],
#   [ 2.9, -2.6, -1.7,  0.0,  1.4, -2.1, -1.7,  1.7,  0.9],
#   [ 0.1, -2.5,  3.2, -1.7,  1.4, -2.5,  3.1, -1.6, -0.1],
#   [-3.6, -2.1, -0.5,  4.1, -1.6,  0.6, -1.3,  4.4, -0.8],
#  ],
#  [[ 0.7,  1.1, -0.6, -0.6,  0.3, -0.7,  0.2,  1.0, -0.2, -0.7, -1.0, -0.9,  0.4, -0.9, -0.8, -0.5, -1.1],
#   [-0.6, -0.9, -0.3, -0.9,  0.2, -0.1,  0.0,  0.3,  0.8, -0.7,  0.5, -0.4, -0.3, -0.8, -0.3, -0.5, -0.4],
#   [-1.6, -0.5, -1.1,  0.2,  0.2, -1.5,  0.5, -0.7,  0.2, -0.9,  0.6, -0.3,  0.3,  0.0,  0.4, -0.1, -1.4],
#   [ 2.0,  3.3, -0.1, -1.3,  3.2,  7.0, -6.3,  0.5,  4.6, -3.8, -5.1,  1.3, -1.0,  1.5,  0.3, -0.7, -0.8],
#   [-1.5,  0.5, -0.5, -0.1, -0.9, -1.5, -0.6,  0.8, -0.6, -1.1,  1.3, -0.3, -0.2,  0.2,  0.8, -1.4, -0.5],
#   [-2.1,  1.2,  1.2, -3.7,  0.3,  2.0, -1.9,  1.1,  1.6,  0.8, -0.8,  0.1, -0.0, -0.3,  1.0, -0.4, -0.2],
#   [ 1.1,  2.4,  4.2, -1.1,  2.2, -7.7,  2.3,  1.1,  2.0,  3.5, -3.4,  0.5,  3.1, -3.7,  0.8,  5.4,  0.2],
#   [-5.1,  1.4, -1.5,  1.4, -0.6, -5.4, -2.1,  2.1,  1.1, -1.5,  1.0,  0.1, -2.6,  0.3,  5.1, -2.7, -1.4],
#  ],
#  [[-0.7,  0.2,  0.9, -12.0,  1.4, -4.3, -11.1,  9.8,  5.4]],
# ]

# 7 bits
# bits = [n[0], n[1], n[2], n[3], n[4], n[5], n[6]]
# [[[-5.8,  3.6,  1.9,  1.1,   3.5,  2.1,  3.3, -4.9],
#   [-3.0,  5.4,  6.8,  2.7,  -5.6,  4.6, -6.4, -1.6],
#   [-5.1,  0.2,  4.5,  2.3,  -1.9, -2.3,  0.0, -1.0],
#   [ 0.2,  2.2, -2.7,  4.8,   0.1, -3.0, -1.7, -0.7],
#   [-2.6,  4.3, -4.8,  3.6,  -3.2,  3.3, -6.0,  2.6],
#   [-3.0,  2.5,  1.1, -4.1,   1.5,  6.5, -3.3, -4.1],
#   [-1.7, -5.8,  2.2,  6.2,  -0.5, -6.8,  3.7,  2.4]],
#  [[-8.0,  9.6, -7.6,  8.6, -12.3, -9.4, -9.6,  5.4]],
# ]

# 8 bits
# bits = [n[0], n[1], n[2], n[3], n[4], n[5], n[6], n[7]] # ~> NameError: undefined local variable or method `n' for main:Object
# [[[-8.8,  3.0,  9.2,  5.0, -4.8,  5.6, -5.8,  6.1, -6.1],
#   [-1.8,  2.3, -2.6, -5.6,  0.1,  6.0, -4.7, -5.7, -3.0],
#   [-3.6, -4.1,  6.5, -0.6, -2.8, -2.6,  2.4, -2.3,  1.0],
#   [ 2.4, -9.1, -3.1,  7.8, -3.7, -8.9, -2.8,  5.6,  6.3],
#   [-2.0,  4.0, 11.0,  3.3, -6.0,  0.7, -7.0,  1.6, -3.0],
#   [ 0.7, -7.2,  2.8,  4.5, -3.6, -1.5,  2.7, -0.1, -3.5],
#   [-8.9,  5.5,  4.8, -4.1,  5.6,  4.8,  5.5, -4.0, -6.4],
#   [-4.0, -6.7, -3.6,  5.5,  2.5, -6.9,  7.8, -4.1, -0.4],
#   [ 1.1, -3.5, -6.7, -2.8,  2.3, -4.7,  6.3, -4.6, -2.2]
#  ],
#  [[-14.6, -13.9, -9.4, -10.8, 13.7, 10.6, -10.7, -11.0, 12.7,  5.2]],
# ]

primes_8bit_integerized.rb

def is_prime?(n)
  [[[-9,  3,  9,  5, -5,  6, -6,  6, -6],
    [-2,  2, -3, -6,  0,  6, -5, -6, -3],
    [-4, -4,  7,  0, -3, -3,  2, -2,  1],
    [ 2, -9, -3,  8, -4, -9, -3,  6,  6],
    [-2,  4, 11,  3, -6,  1, -7,  2, -3],
    [ 1, -7,  3,  4, -4, -2,  3,  0, -3.5],
    [-9,  6,  5, -4,  6,  5,  5, -4, -6],
    [-4, -7, -4,  5,  2, -7,  8, -4,  0],
    [ 1, -3, -7, -3,  2, -5,  6, -5, -2]],
  [[-15,-14,-9,-11,14,11,-11,-11,11,5]]]
  .inject(8.times.map{|i|n[i]}){|l,r|r.map{|s|1/(1+Math::E**[*l,1].zip(s).inject(0){|x,(n,s)|x-n*s})}}[0]>0.5
end

require 'prime'
(256).times.all? { |n| is_prime?(n) == n.prime? } # => true