Why is my fimplicit plot empty?

syms x(t)

ode45 = diff(x,t,2) + ((4.2/(t + 3))/2)*x == 0;

Dx = diff(x);
DDx = diff(Dx);

cond1 = x(0) == 0;
cond2 = Dx(0) == 5;
conds = [cond1 cond2];

xSol = dsolve(ode45,conds);


fimplicit (@(t) xSol(t),[-20 20 -20 20])



xlim([-10 10]);
ylim([-10 10]);
grid on;
  

I am trying to plot this equation, the plot opens up but its all empty.

Warnings: Unable to find explicit solution.

> In dsolve (line 201)

In test (line 12)

Answer 1

[Stephan]

The warning means, that Matlab did not find an analytical solution - solve numeric:

syms x(t) Dxt(t)
ode = diff(x,t,2) + ((4.2/(t + 3))/2)*x == 0;
[ode, vars] = reduceDifferentialOrder(ode, x);
[V, S] = odeToVectorField(ode);
fun = matlabFunction(V,'Vars',{'t','Y'});
[t, xSol] = ode45(fun,[0 200],[0 5]);
plot(t,xSol)
grid on;

[Rasandemusen]

One more thing, does the orange curve show the derivate of the blu function?

Thank you for the help!

[Stephan]

Yes, the order of the variables is saved in vector S. in this order Y[1] and Y[2] are saved in the functionHandle.