Hi Bill,

On 05/02/2018 03:32 AM, null null wrote:

Hi,

I am a new user of SfePy and finite element programming in general, and I
have started my own finite element project last week. After comparing SfePy
with other packages like FEniCS and GetFEM++ I have decided to give SfePy a
try. My problem is close to a diffusion problem. I have a fair amount of
scientific Python experience in general, including some VTK.

I know I can export the computation result to VTK files in Unstructured
Grid format, which is performed at the end of many examples. My question
is: how can I access the final result, at each vertex, directly from the
Python program itself, saving the result into say a Numpy array or
equivalent data structure.

In static problems (no time stepping), you can simply call state() or state.get_parts() to get the solution vectors as numpy arrays of DOFs in the FE nodes - those nodes correspond to mesh vertices for linear FEM. In time-dependent problems, the same holds, but the state returned by the solver is the final state - if you need to access the DOFs in all time steps, see below.

For example, the Time Thermal Interactive example
<http://sfepy.org/doc-devel/examples/diffusion/time_poisson_interactive.html>
exports domain.01.vtk to domain.02.vtk, containing points, cells, and
temperature at each point ("SCALARS T float 1.") Is there a way to access
these numbers directly at the end of the computation, from say the Problem
variable pb or State variable state0? I feel like this is probably an easy
task but I could not figure out on my own just by looking into the State
and Problem variables.

I need these values directly in Python as I have other part of my model
that takes the temperature values at these vertices. Since the other
computation will use the same mesh I would like to have the mesh and all
solved values.

Check the example [1] to see how to setup a custom hook (or callback) function that is called in each time step, and where you can, for example, store the state. Essentially, you need to:

1. get the standard callbacks of a time-stepper:

init_fun, prestep_fun, _poststep_fun = pb.get_tss_functions(state0)

2. define your own poststep_fun(), where you call the standard _poststep_fun() and then do what you need - you can access the DOF arrays of variables using something like pb.get_variables()['T']().

3. call the time stepper, as in [1]

tss(state0.get_vec(pb.active_only),
    init_fun=init_fun, prestep_fun=prestep_fun, poststep_fun=poststep_fun,
    status=tss_status)

Let me know if you need more help - the current implementation of the time-stepping solvers is very new and not much documented.

r.

[1] http://sfepy.org/doc-devel/examples/diffusion/time_poisson_interactive.html

Thanks!

Bill



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