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1; # Prevent Octave from thinking that this is a function
   # though one is defined here
   
  function w = f(x2,y2,z2,c,r,e) 
   x  = (x2-c(1))/r(1);
   y  = (y2-c(2))/r(2);
   z  = (z2-c(3))/r(3);
   # function at origin must be <0, and >0 far enough away.  w=0 defines the surface
   s=cos(x*15).*y.*(y-1).*(y+1);
   w = x.^2+y.^2+(z+0.3*x.^2-0.15*y.^2+0.25*s).^2-1;

   endfunction;