function exm110633_1
shg;R0=1;								
a=12*R0;b=9*R0;T0=2*pi;							
T=5*T0;dt=pi/100;t=[0:dt:T]';
f=sqrt(a^2-b^2);							
th=12.5*pi/180;										
E=exp(-t/20);											
x=E.*(a*cos(t)-f);y=E.*(b*cos(th)*sin(t));z=E.*(b*sin(th)*sin(t));
plot3(x,y,z,'g')										
[X,Y,Z]=sphere(30);X=R0*X;Y=R0*Y;Z=R0*Z;		
grid on,hold on,surf(X,Y,Z),shading  interp	
x1=-18*R0;x2=6*R0;y1=-12*R0;y2=12*R0;z1=-6*R0;z2=6*R0;
axis([x1 x2 y1 y2 z1 z2])						
view([117 37]),
p=input('Please input the comet'' length coeffient (the default value is 0.1): ');
if ~isempty(p),
    p=0.1;
end
comet3(x,y,z,p),hold off