>	a:=2;b:=5;c:=sqrt(a^2+b^2);

>	x:=a+c*cos(t);y:=b*sin(t);z:=a*sin(t);

>	p1:=plot3d([x*cos(s)-y*sin(s),x*sin(s)+y*cos(s),z],s=0..Pi,t=0..2*Pi,scaling=constrained,grid=[50,50],color=green):

>	p2:=plot3d([x*cos(s)-y*sin(s),x*sin(s)+y*cos(s),z],s=Pi..2*Pi,t=0..2*Pi,scaling=constrained,grid=[50,50],color=blue):

>	with(plots);

Warning, the name changecoords has been redefined

>	display(p1,p2);

>