drawing.rb

require 'parable'

p = Parable.new

x_start = 0
y_start = 0

p.point(x_start,y_start)

x_finish = 200
y_finish = 200

p.point(x_finish,y_finish)

xv = (x_finish.to_f-x_start.to_f)/2
yv = 100.0

distance = x_finish-xv

(0..250).each do |x|

  k = (-yv)/distance**2

  fx = k*((x-xv)**2)+yv
  
  puts "#{x},#{fx}"
  
  p.point(x,fx)
end

p.output

parable.rb

require 'rubygems'
require 'rmagick'

class Parable
  def initialize
    @canvas = Magick::Image.new(250,250)
    @draw = Magick::Draw.new
    File.delete('testing.gif') if File.exists? 'testing.gif'
  end
  
  def point(x,y)
    @draw.point(x,y)
  end
  
  def output
    @draw.draw(@canvas)
    @canvas.write('testing.gif')
  end
end