class MoreMath::LinearRegression

def compute
  size = @image.size
  sum_xx = sum_xy = sum_x = sum_y = 0.0
  @domain.zip(@image) do |x, y|
    x += 1
    sum_xx += x ** 2
    sum_xy += x * y
    sum_x += x
    sum_y += y
  end
  @a = (size * sum_xy - sum_x * sum_y) / (size * sum_xx - sum_x ** 2)
  @b = (sum_y - @a * sum_x) / size
  self
end