Hi, I'm trying to generate some figure with R, into an org session. Firstly I use the code in the org site. The problem is that the code do not generate any figure.

This is the code:

#+TITLE:Test 
#+AUTHOR: Your Name
#+EMAIL: your-email@server.com
#+BABEL: :session *R* :cache yes :results output graphics :exports both :tangle yes 

* Example of Org-Babel for R Literate Programming
** R text output
A simple summary. 
#+begin_src R 
  x <- rnorm(10)
  summary(x)
#+end_src

** R graphics output
Note we use the object =x= generated in previous code block, thanks to
the header option =:session *R*=.  The output graphics file is
=a.png=. 

#+begin_src R  :file a.png
  y <- rnorm(10)
  plot(x, y)
#+end_src

Same plot with larger dimension:

#+begin_src R  :file b.png :width 800 :height 800
  plot(x, y)
#+end_src

Where do I wrong?

Best
Riccardo