[Numpy-discussion] nltk dispersion plot problem

[Gias]

I am using Ubuntu 11.04 (natty) in my laptop and Python 2.7. I installed nltk 
(2.09b), numpy (1.5.1), and matplotlib(1.1.0). The installation is global and I 
am not using virtualenv.When I try (text4.dispersion_plot(["citizens",
"democracy", "freedom", "duties", 
"America"])) in terminal (gnome
terminal 2.32.1), the plot 
is not showing up. There is no error message, just a second or two interval 
before the last (>>>) shows up.