
plvpor: Specify viewport using coordinates 

DESCRIPTION:

    This function is used in examples
    2,6-8,10,11,15,16,18,21,23,24,26,27,31. 

SYNOPSIS:

plvpor(xmin, xmax, ymin, ymax)

ARGUMENTS:

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

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

    ymin (PLFLT, input) :    The normalized subpage coordinate of the
    bottom edge of the viewport. 

    ymax (PLFLT, input) :    The normalized subpage coordinate of the top
    edge of the viewport. 
