Hi everyone,

I have the following weak formulation:

```
ax = dot((Xh / k),phi)*dx + vare*inner(grad(Xh),grad(phi))*dx
Lx = inner((Xh0 / k),phi)*dx + inner(kp*u10*n_oriented,phi)*dx + inner(lamb*n_oriented,phi)*dx
```

The value of `lamb`

is uniform over the domain but changes over time. I am defining the matrices, vector and solver like this

```
bilinear_form = form(ax)
linear_form = form(Lx)
Ax = assemble_matrix(bilinear_form)
Ax.assemble()
b = create_vector(linear_form)
assemble_vector(b, linear_form)
b.ghostUpdate(addv=PETSc.InsertMode.ADD_VALUES,
mode=PETSc.ScatterMode.REVERSE)
solverx = PETSc.KSP().create(mesh.comm)
solverx.setOperators(Ax)
solverx.setType(PETSc.KSP.Type.PREONLY)
solverx.getPC().setType(PETSc.PC.Type.LU)
```

I tried putting the line `assemble_vector(b, linear_form)`

inside the for loop, but it wasnâ€™t successful.

How can I implement this?

Thank you.