Ruby script to draw a graph by gnuplot.(Ex.2)

gnuplot_2.rb

#! /usr/local/bin/ruby
#-----------------------------------------------
# Ruby script to draw a graph by gnuplot.(Ex.2)
#-----------------------------------------------
require 'gnuplot'

Gnuplot.open do |gp|
  Gnuplot::Plot.new(gp) do |plot|
    plot.terminal "png enhanced font 'IPA P ゴシック' fontscale 1.2"
    plot.output   "gnuplot_2.png"
    plot.title    "作成例２"
    plot.xlabel   "x"
    plot.ylabel   "y=x^3-2x+2"
    plot.grid

    x = (-20..20).collect { |v| v.to_f / 10.0 }
    y = x.collect { |v| v ** 3 - 2 * v + 2}

    plot.data << Gnuplot::DataSet.new([x, y]) do |ds|
      ds.with      = "linespoints"  # 点のみなら "points"
      ds.linewidth = 2
      ds.linecolor = 3
      ds.notitle
    end
  end
end