// ------------------------------
//  The 16 nodal quartic surface
//  colored light demo
// ------------------------------

//  set some constants

double pi=3.145;
double mue2 =2/3;
double lam =-3/7;

//  fix scaling

scale_x = 0.11;
scale_y = 0.11;
scale_z = 0.11;

//  fix rotation

rot_x=6.2478;
rot_y=1.2318;
rot_z=2.1903;

spec_z=30;
perspective=central;

//  fix clip-values 

radius=10;

//  fix light

ambient=30;
illumination=7;

light1_x =60;
light1_y =40;
light1_z =0;
light1_red=255;
light1_green=5;
light1_blue=5;
light1_vol=50;

light2_x =100;
light2_y =00;
light2_z =-20;
light2_red=0;
light2_green=255;
light2_blue=0;
light2_vol=50;

light3_x=-70;
light3_y=50;
light3_z=-0;
light3_red=0;
light3_green=0;
light3_blue=250;
light3_vol=40;

//  fix surface properties 

smoothness=50;
diffuse=70;

surface_red=232;
surface_green=230;
surface_blue=230;
inside_red=230;
inside_green=180;
inside_blue=30;

//  the formula

poly p = 1-x-y+z;
poly q = 1+x+y+z;
poly r = 1-x+y-z;
poly s = 1+x-y-z;

poly s2= x^2+y^2+z^2;

poly pqrs2 = p*q*r*s;

surface = (s2 -mue2)^2 + lam*pqrs2;

//  draw it

clear_screen;
draw_surface;