In your isolate call, s no longer exists as a variable. You can create ‘g3’ eartlier in the code (when it does exist), and then use ‘g3’ later. At the end of the code, all the variables have been solved for, so I am not sure what you want to do with ‘g3’ at that point.
syms x y z s
laenge = 3;
breite = 1;
hoehe = 1;
ellipsoid(0,0,0, laenge,breite,hoehe);
axis equal
xlabel('X-Achse')
ylabel('Y-Achse')
zlabel('Z-Achse')
hold on
% Parameterequation Ellipsoid
e1 = (x^2/laenge^2) + (y^2/breite^2) + (z^2/hoehe^2) == 1;
% Parameterequation Line
g2 = [x;y;z] == [4;0;0] + s.*[-1;0;0];
g3 = isolate(g2(1),s)
E = [e1;g2];
t = solve(E, x, y, z, s);
x = t.x
y = t.y
z = t.z
s = t.s
%snew = subs(x)
%s = [2;2];
%snew = subs(g2(1),s,[2;2])
.
