ex_trainer/lib/growth/calc/centile.ex

defmodule Growth.Calc.Centile do
  @moduledoc """
    measures =
      [
        [30, -1.7862, 16.9392, 0.1107],
        [14, -1.3592, 20.4951, 0.12579],
        [19, -1.6318, 16.049, 0.10038]
      ]
    Enum.map(measures, &apply(Growth.Calc.Centile, :compute, &1))
  """

  alias Growth.Calc.ZScore

  # TODO: (jpd) add documentation and typespecs

  def compute(y, l, m, s) do
    zscore = ZScore.raw(y, l, m, s)

    if -3 <= zscore and zscore <= 3 do
      m * :math.pow(1 + l * s * zscore, 1 / l)
    else
      :na
    end
  end
end