syms dependent on time with dots

Hello,

I have a question. I want to implement the time derivative of u in the following way in Matlab:

syms theta t
syms phi t
u = 5*cos(theta)+phi
u_dot = diff(u,t);

When I execute this code, I end up with u_dot = 0, which is not what I want.

Does someone maybe know how to get the u_dot in the above form?

Thanks in advance!

Answer 1

[KSSV]

syms A theta(t) phi(t) ;
u = A*cos(theta)+phi 
du = diff(u,t)

[Tobias]

Thank you for your help!

Yes this is what I wanted. I just had to use the syms function once.

But in my real code, u is a vector. It has the same structure as in this example:

syms A theta(t)  phi(t);
u = [A*cos(phi)*theta;sin(phi)*phi];
du = diff(u,t);

Now u and du are converted to 1x1 symfun functions, but I actually want it to be a vector output as well.

I got this output for du:

A*cos(phi(t))*diff(theta(t), t) - A*sin(phi(t))*theta(t)*diff(phi(t), t)

sin(phi(t))*diff(phi(t), t) + cos(phi(t))*phi(t)*diff(phi(t), t)

But I want the output to be in 2x1 vector form. Do you maybe know how to do this?

Thanks!