def run_simulation()
        # create a canvas of size 200 X 200
        Canvas.init(200, 200, "Simulation")
        # initialize matrix a
        a = Array.new(20)
        for i in 0..19 do
                a[i] = Array.new(20)
                for j in 0..19 do
                        a[i][j] = 0
                end
        end
	# infect one random person
        a[rand(20)][rand(20)] = 1
        display(a)
	sleep(2)
	# run simulation until everyone is immune
        while !all_immune(a) do
                a = update(a)
                display(a)
                sleep(2)
        end
end