Genetic Algorithms in Elixir:P67 fitness_function correction

[adkelley]

def fitness_function(chromosome) do
   chromosome
   |> Enum.map(fn {roi, risk} -> 2 * roi - risk end) 
   |> Enum.sum()
end

should be:

def fitness_function(chromosome) do
  chromosome.genes
  |> Enum.map(fn {roi, risk} -> 2 * roi - risk end) 
  |> Enum.sum()
end