plsvpa: Specify viewport in absolute coordinates 

DESCRIPTION:

    Alternate routine to plvpor for setting up the viewport.  This routine
    should be used only if the viewport is required to have a definite
    size in millimeters.  The routine plgspa is useful for finding out the
    size of the current subpage. 

SYNOPSIS:

plsvpa(xmin, xmax, ymin, ymax)

ARGUMENTS:

    xmin (PLFLT, input) :    The distance of the left-hand edge of the
    viewport from the left-hand edge of the subpage in millimeters. 

    xmax (PLFLT, input) :    The distance of the right-hand edge of the
    viewport from the left-hand edge of the subpage in millimeters. 

    ymin (PLFLT, input) :    The distance of the bottom edge of the
    viewport from the bottom edge of the subpage in millimeters. 

    ymax (PLFLT, input) :    The distance of the top edge of the viewport
    from the bottom edge of the subpage in millimeters.