patrickdm

patrickdm

Genetic Algorithms in Elixir: Ch4. errata in evolve function (page 59)

At the beginning of page 59, in chapter 4

alter the evolve function to track a generation parameter, like this:

def evolve(problem, generation, opts \\ []) do
  # ...
  if terminate?(population, generation) do
    # ...
  else
    generation = generation + 1
    ...
    |> evolve(population, generation opts)
  end
end

The evolve definition is missing the first param population;
a comma is also missing between the last two params of the evolve call, at the end of the function’s body,

Edit: I guess problem should be in the params of the recursive call to evolve in place of population , and as prefix in the terminate? call.

We have also to include an initial value for generation in run/2’s evolve call, to avoid an>

(ArithmeticError) bad argument in arithmetic expression

due to an uninitialized generation in the + 1 operation. (I’m starting from generation 0)

Corrige:


def run(problem, opts \\ []) do
  population = initialize(&problem.genotype/0, opts)
  first_generation = 0

  population
  |> evolve(problem, first_generation, opts)
end

def evolve(population, problem, generation, opts \\ []) do
  # ...
  if problem.terminate?(population, generation) do
    # ...
  else
    generation = generation + 1
    ...
    |> evolve(problem, generation, opts)
  end
end

(Hope I’m not bothering anyone with this small corrections, I’m really enjoying the book)

Most Liked

seanmor5

seanmor5

Author of Genetic Algorithms in Elixir

Thank you for finding all these things :slight_smile:. I’m glad you’re enjoying the book! I’ll go back and fix this one as well.

patrickdm

patrickdm

It is a pleasure to be helpful, I’m just reading the book, studying the concepts and putting the code at work, so the small glitches in the redaction wake up the little debugger-daemon in me… :bug::smiling_imp: They actually help me to focus and understand the overall logic and goals! Also I know how hard is to spot them when you know every and each word of your book by memory. I’m glad to be of some help, while learning so much!

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