Hi everyone,

I am trying to solve a set of PDEs coupled with one ODE. I was able to solve the system of PDEs assuming the variable defined by the ODE stays constant. However, when I try to add the ODE, I am getting a syntax error. To reproduce the error, I have added a minimal script to just solve the ODE. I tried to follow the example in the post Can one solve system of ODE with fenics?. But I get a syntax error for my problem. Here is a minimal code.

```
from fenics import *
mesh = IntervalMesh(200, 0, 2)
V = FunctionSpace(mesh,'CG',1)
v = TestFunctions(V)
u = Function(V)
dp = Constant(0.002) # Diameter of catalyst particle m
eps = Constant(0.40) # epsilon
muf = Constant(3.78E-5) # Average viscosity of gas, Pa.s
rof = Constant(1565.85) # Average density
Vz_in = Constant(1.0) # Inlet superficial velocity m/s
P_in = 5.0E+5 # Inlet Pressure Pa
bc = DirichletBC(V,P_in,'near(x[0], 0)')
F_P = u.dx(0)*v*dx + (150*(1-eps)**2*muf/(dp**2*eps**3))*Vz_in*v*dx + \
1.75*(1-eps)*rof*1e-3*Vz_in**2/(dp*eps**3)*v*dx
```

```
TypeError Traceback (most recent call last)
<ipython-input-19-399fb5bf64b8> in <module>
----> 1 F_P = u.dx(0)*v*dx + (150*(1-eps)**2*muf/(dp**2*eps**3))*Vz_in*v*dx + \
2 1.75*(1-eps)*rof*1e-3*Vz_in**2/(dp*eps**3)*v*dx
TypeError: can't multiply sequence by non-int of type 'Indexed'
```

Can you please help me identify the issue?

Thank you.