Swarm algorithm visualised in gnuplot

swarm.rb

#! /bin/ruby
# swarm algorithm

require 'gnuplot'

class Particule
    attr_reader :x, :y
    def initialize(size_x, size_y)
        @size_x = size_x
        @size_y = size_y
        @x      = rand(@size_x)
        @y      = rand(@size_y)
        @vx     = rand(@size_x)/20.to_f
        @vy     = rand(@size_y)/20.to_f
        @ox     = @x
        @oy     = @y
    end

    def objective(x, y)
        (x - @size_x / 2.to_f)**2 + (y - @size_y / 2.to_f)**2
    end

    def iterate(delta, ogx, ogy, w)
        @x += delta * @vx
        @y += delta * @vy
        @x = -@x if @x < 0
        @x = 2 * @size_x - @x if @x > @size_x
        @y = -@y if @y < 0
        @y = 2 * @size_y - @y if @y > @size_y

        if (objective(@x, @y) < objective(@ox, @oy))
            @ox = @x
            @oy = @y
        end

        r1 = rand(200) / 200.to_f
        r2 = rand(200) / 200.to_f
        @vx = w * @vx + r1 * (@ox - @x) / delta + r2 * (ogx - @x) + delta
        @vy = w * @vy + r1 * (@oy - @y) / delta + r2 * (ogy - @y) + delta
    end
end

class Swarm
    def initialize
        @delta = 0.5
        @w = 1.4
        @size = 50
        @swarm = []
        @size_x = 20
        @size_y = 20

        @size.times { |i| @swarm.push(Particule.new(@size_x, @size_y)) }

        @xg = @swarm.map { |i| i.x }.inject(0) { |sum, i| sum += i } / @size
        @yg = @swarm.map { |i| i.y }.inject(0) { |sum, i| sum += i } / @size

        @ox = @xg
        @oy = @yg
    end

    def objective(x, y)
        (x - @size_x / 2.to_f)**2 + (y - @size_y / 2.to_f)**2
    end

    def iterate
        @swarm.each { |i| i.iterate(@delta, @ox, @oy, @w) }

        @xg = @swarm.map { |i| i.x }.inject(0) { |sum, i| sum += i } / @size
        @yg = @swarm.map { |i| i.y }.inject(0) { |sum, i| sum += i } / @size

        if (objective(@xg, @yg) < objective(@ox, @oy))
            @ox = @xg
            @oy = @yg
        end

        @w *= 0.95
    end

    def go(iter)
        Gnuplot.open do |gp|
            iter.times do |_|
                iterate
                x = @swarm.map { |i| i.x }
                y = @swarm.map { |i| i.y }

                sleep 0.1
                Gnuplot::Plot.new( gp ) do |plot|
                    plot.title  "Swarm algorithm"
                    plot.xrange "[0:20]"
                    plot.yrange "[0:20]"
                    plot.data << Gnuplot::DataSet.new( [x, y] ) do |ds|
                        ds.with = "points"
                        ds.notitle
                    end
                end
            end
        end
    end
end

Swarm.new.go(100)