pllightsource: Sets the 3D position of the light
source 

DESCRIPTION:

    Sets the 3D position of the light source for use with plsurf3d. 

SYNOPSIS:

pllightsource(x, y, z)

ARGUMENTS:

    x (PLFLT, input) :      X-coordinate of the light source. 

    y (PLFLT, input) :      Y-coordinate of the light source. 

    z (PLFLT, input) :      Z-coordinate of the light source.