Hi Robert,

From the poisson.py I would like to probe the flux of grad(T) over a surface (Gamma_Left or Gamma_right), but I am not sure which term to use...

I would use it in electrostatics (temperature is replaced by voltage), to compute the resistance of the volume imposing a voltage of 1 across two surfaces with dirichlet conditions and computing the electrical current. For a ohmic conductor, j = \sigma E = - \sigma grad(V), \sigma being the conductivity. j being the current density, the current intensity thru a surface is the flux of j thru that surface. For the case of homogenous \sigma, the term asked for above would do...


Le dimanche 26 août 2012 22:55:49 UTC+2, Robert Cimrman a écrit :
On 08/26/2012 12:32 PM, Alec Kalinin wrote:
> Hi Robert,
> Did you mean "linear_elastic_probes.html" instead of
> "linear_elastic_tractions.html" example? I found the
> "linear_elastic_probes.html" very useful example for my purposes to probe a
> solution in the given (x, y, z) points. Also the documentation
> "src/sfepy/fem/probes.html" gives all necessary information to help me
> implement what I want to do. Thank you!

Sorry, I cut&pasted a wrong url, the correct one is [1]. But you found
another one that solves the problem.

> But, despite this, could you tell me more about low-level way to evaluate a
> variable in the given (x, y, z) point?

It's exactly how the probes do that: the key function is
variable.evaluate_at() [2], where variable is an unknown or parameter
variable. It takes just one compulsory parameter - the coordinates of
points in which you wish to evaluate the variable. You can get the
variables of a problem by problem.get_variables(), where problem is the
second argument of the post_process_hook function.

Best regards,

[1] http://sfepy.org/doc-devel/primer.html#probing
[2] http://sfepy.org/doc-devel/src/sfepy/fem/variables.html,

> On Sunday, August 26, 2012 12:47:50 AM UTC+4, Robert Cimrman wrote:
>> Hi Alec,
>> On 08/25/2012 05:45 PM, Alec Kalinin wrote:
>>> Dear SfePy users,
>>> Is it possible to evaluate a solution not only in the FEM mesh node, but
>> in
>>> any arbitrary point in the domain with the given (x, y, z) coordinates?
>> Yes, it is possible. Either, you could use a probe as described in the
>> Primer [1] - the available probes are described in [2]. Or, you could
>> directly evaluate a variable in given points - this is a bit low-level
>> operation, but I could provide you instructions, if the probes are not
>> enough for you.
>> Cheers,
>> r.
>>> For example, consider Dirichlet problem for Poisson equation. We apply
>>> essential boundary conditions on the surface nodes and after the problem
>>> has been solved we have the solution vector, i.e. vector of values in
>> the
>>> FEM mesh nodes. But I want to know the solution in point v(x, y, z) that
>> is
>>> not FEM mesh node. What is the best way to obtain solution in this point
>> v?
>>> Sincerely,
>>> Alec Kalinin
>> [1] doc-devel/examples/linear_elasticity/linear_elastic_tractions.html
>> [2] http://sfepy.org/doc-devel/src/sfepy/fem/probes.html