Ruby Implementation of Riemann Sum (left and right solution)

riemann_sum.rb

# https://en.wikipedia.org/wiki/Riemann_sum
class RiemannSum

  def initialize(f, v_start, v_end, n_step)
    @f = f
    @v_start = v_start
    @v_end = v_end
    @n_step = n_step
    @step_size = (v_end - v_start) / (n_step * 1.0)
  end

  def solve_left
    sum = 0
    s, e = @v_start, @v_end
    @n_step.times do
      sum += @f.call(s) * @step_size
      s = [s + @step_size, e].min
    end
    sum
  end

  def solve_right
    sum = 0
    s = @v_start + @step_size
    e = @v_end
    @n_step.times do
      sum += @f.call(s) * @step_size
      s = [s + @step_size, e].min
    end
    sum
  end
end

# \displaystyle\int_{3}^{10} \left( -10x^{2}+3x+6\right) dx
f = ->(x) { -10*(x**2) + 3*x + 6 }
r = RiemannSum.new(f, 3, 10, 2)
 => #<RiemannSum:0x00000001f63e88 @f=#<Proc:0x00000001f75e58@(irb):2 (lambda)>, @v_start=3, @v_end=10, @n_step=2, @step_size=3.5> 

r.solve_left
# => -1652.0
r.solve_right
# => -4763.5