The plots generated by the plotting commands can be used in various
different ways. One thing you might want to do is to write the
output to a file in a given graphics format
(out);
another is to preview it directly on the screen
(swing).
By default one or other of these will happen depending on whether you
specify an output file. However there are other possibilities;
these are listed in the following subsections.
Except for display to the screen, these modes should work happily
on a headless machine (one with no graphics display, as may be the case
for a web server).
When running headless, you may find it necessary to
set the java system property
"java.awt.headless" to true
- see Section 3.3.
The default output mode is auto,
which means that output is to a file if an output file is specified,
or to the screen if it is not. So in most cases you don't need to specify the
omode parameter explicitly.