rotate the sphere around the circle of the torus

Please help us solve the problem. You must rotate the sphere around the circle of the torus

%Строим тор
R=20;
r=5;
[a, b] = meshgrid(0:20/180*pi:2*pi);
X=((R-r)+r*cos(a)).*cos(b);
Y=((R-r)+r*cos(a)).*sin(b);
Z=r.*sin(a);
hsurf = surf(X,Y,Z,'FaceColor','interp','FaceAlpha',0.2,'EdgeAlpha',0.3);
axis equal; hold on
%Создаем шарик 1
hold on
[x,y,z]=sphere;
x1=x-15;
z1=z;
y1=y;
l1=surf(x1,y1,z1);

Answer 1

[Atsushi Ueno]

"rotate the sphere around the circle of the torus" means like this?

%Строим тор
R=20;
r=5;
[a, b] = meshgrid(0:20/180*pi:2*pi);
X=((R-r)+r*cos(a)).*cos(b);
Y=((R-r)+r*cos(a)).*sin(b);
Z=r.*sin(a);
hsurf = surf(X,Y,Z,'FaceColor','interp','FaceAlpha',0.2,'EdgeAlpha',0.3);
axis equal; hold on
%Создаем шарик 1
hold on
[x,y,z]=sphere;
for th1 = 0:45/180*pi:2*pi
for th2 = 0:45/180*pi:2*pi
x1=x + ((R-r) + r * cos(th1)) * cos(th2);
y1=y + ((R-r) + r * cos(th1)) * sin(th2);
z1=z +          r * sin(th1);
l1=surf(x1,y1,z1);
end
end

Answer 2

[KSSV]

R=20;
r=5;
[a, b] = meshgrid(0:20/180*pi:2*pi);
X=((R-r)+r*cos(a)).*cos(b);
Y=((R-r)+r*cos(a)).*sin(b);
Z=r.*sin(a);
hsurf = surf(X,Y,Z,'FaceColor','interp','FaceAlpha',0.2,'EdgeAlpha',0.3);
axis equal; hold on
%??????? ????? 1
hold on
[x,y,z]=sphere;
x1=x;
z1=z;
y1=y;
l1=surf(x1,y1,z1);
%% Animation 
th = linspace(0,2*pi); 
xc = R*cos(th) ; 
yc = R*sin(th) ; 
% Draw sphere around torus 
for i = 1:100
  figure(1)
  hold on
  surf(X,Y,Z,'FaceColor','interp','FaceAlpha',0.2,'EdgeAlpha',0.3);
  surf(x1+xc(i),y1+yc(i),z1)
  hold off
end

  

[Adam Danz]

Faster & more efficient,

% Draw sphere around torus
hold on
for i = 1:100
    surf(x1+xc(i),y1+yc(i),z1)
    drawnow
end

otherwise you're redrawing the torus over and over again. Calling figure() repetitively also slows things down.