function sf3d(n, a)

  u=[-pi:.05:pi];
  v=[-pi/2:.05:pi/2];
  nu=length(u);
  nv=length(v);
  
  for i=1:nu
    for j=1:nv
      raux1=abs(1/a(1)*abs(cos(n(1).*u(i)/4))).^n(3)+abs(1/a(2)*abs(sin(n(1)*u(i)/4))).^n(4);
      r1=abs(raux1).^(-1/n(2));
      raux2=abs(1/a(1)*abs(cos(n(1)*v(j)/4))).^n(3)+abs(1/a(2)*abs(sin(n(1)*v(j)/4))).^n(4);
      r2=abs(raux1).^(-1/n(2));
      x(i,j)=r1*cos(u(i))*r2*cos(v(j));
      y(i,j)=r1*sin(u(i))*r2*cos(v(j));
      z(i,j)=r2*sin(v(j));
    endfor;
  endfor;
  mesh(x,y,z);
endfunction;