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**                         Technical Reference                          **
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 (1) Every instance of a GnuPlot class corresponds to the spawn of a
     gnuplot process which takes commands through a unix pipe.

 (2) The GnuPlot class defines by default a Layout internal instance
     which can be replaced by the setLayout() method.
     The default Layout provides a simple 1×1 subdivision of the canvas.

 (3) Any element which is able to modify somehow the canvas must be a
     subclass of the Drawable abstract class. This forces to implement
     three methods: init(), display() and reset(), which respectively
     prepare the canvas, display what must be displayed and reset the
     canvas to the previous settings. The Drawable class also implements a
     run() method which executes sequentially init(), display() and
     reset(). The use of run() is not mandatory.