It is well-known that R has several graphics devices — either the screen devices (X11(), windows(), …) or the off-screen devices (pdf(), png(), …). We can query the default graphics device in options(): getOption('device') In a non-interactive session, the default device is pdf(). This is why Sweave has to create a file named Rplots.pdf no
Zero Inflated Models and Generalized Linear Mixed Models with R.
Zuur, Saveliev, Ieno (2012).
