When GNUPLOT is run, it looks for an initialization file to load.
This file is called .gnuplot on Unix systems, and GNUPLOT.INI on
other systems. If this file is not found in the current directory,
the program will look for it in your home directory (under MS-DOS, the
environment variable GNUPLOT should contain the name of this
directory).
If this file is found, GNUPLOT executes the commands in this file.
This is most useful for setting your terminal type and defining any
functions or variables which you use often. The variable pi is
already defined for you.