Numerical integration

# title: Numerical integration
# source: https://rosettacode.org/wiki/Numerical_integration
# category: Rosetta Code
# difficulty: Intro
# summary: Approximate definite integrals with the trapezoidal rule over fixed functions.
# tags: popular, math, calculus, approximation
# vibe: 0.2

def square(value)
  value * value
end

def line(value)
  (3 * value) + 2
end

def trapezoidal_square(start_value, finish_value, steps)
  width = (finish_value - start_value) / steps
  total = (square(start_value) + square(finish_value)) / 2
  step = 1

  while step < steps
    total = total + square(start_value + (step * width))
    step = step + 1
  end

  total * width
end

def trapezoidal_line(start_value, finish_value, steps)
  width = (finish_value - start_value) / steps
  total = (line(start_value) + line(finish_value)) / 2
  step = 1

  while step < steps
    total = total + line(start_value + (step * width))
    step = step + 1
  end

  total * width
end

def run
  {
    integral_of_x_squared: trapezoidal_square(0.0, 1.0, 50),
    integral_of_three_x_plus_two: trapezoidal_line(0.0, 5.0, 50)
  }
end