plwind: Specify world coordinates of viewport boundaries 

DESCRIPTION:

    Sets up the world coordinates of the edges of the viewport. 

SYNOPSIS:

plwind(xmin, xmax, ymin, ymax)

ARGUMENTS:

    xmin (PLFLT, input) :    The world x coordinate of the left-hand edge
    of the viewport. 

    xmax (PLFLT, input) :    The world x coordinate of the right-hand edge
    of the viewport. 

    ymin (PLFLT, input) :    The world y coordinate of the bottom edge of
    the viewport. 

    ymax (PLFLT, input) :    The world y coordinate of the top edge of the
    viewport.