Question: Help with solution of a Coupled system of PDE/ODE

Hi everyone.

I have been experiencing a problem trying to solve a coupled system of 4 differencial equations, 2 PDEs with 2 ODE.

My problem is that a got a message back as I try to solve the system:

"Error, (in pdsolve/numeric/process_IBCs) improper op or subscript selector"

My first question is: Am I defining the IBCs rightly?

If not, I don`t have a clue on how to solve this problem, I really apreciate some help out here.

In advance, thanks for the time of reading it!

Regards

Sergio

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The code is:

diff(Cf(z,t),t)+vmed*(diff(Cf(z,t),z)=k*Apop*(Csat-Cf(z,t))/Vsist      (1)

diff(mpop(z,t),t)+vs(t)*(diff(mpop(z,t),z))=-k*Apop*(Csat-Cf(z,t))   (2)

diff(vs(t),t)=Fr/m                                                                         (3)

diff(z(t),t)=vs(t)                                                                          (4)

the solver that I am using is:

pdsolve(PDEsys,IBCs,numeric,time=t,range=0..L,timestep=1/256,spacestep=1/256)

PDEsys is the name of the system that I gave to it.

The IBCs I defined as follows:

IBCs:={Cf(z,0)=0,Cf(0,t)=0,mpop(z,0)=0,mpop(0,t)=0,vs(0)=0,z(0)=0}

The dependent variables are Cf(z,t), mpop(z,t), vs(t), z(t). I ommited the rest cause the complete routine is too long.

Obs: All the others variables are defined in subrotines and many of them has dependency on the dependent variables, for exemple: Apop=f(mpop), etc...)