I will be taking a few days vacation after Christmas, and I will start=20
coding up the improved system support that I've been hyping up for a=20
while. That should make this a lot simpler.
What you can do in the meantime is add another *system* with some=20
variables that will be used for plotting purposes. If you don't provide=20
an assemble function for this system there should be no linear solve.
Also, sometimes it is useful to have a linear solve to compute your=20
postprocessing variables. For instance, if you have a C0 solution then=20
the stresses aren't uniquely defined at the nodes, but you can solve an=20
L2 projection system to get a smooth stress field. Something like this:
es.add_system("PostProcessing");
es("PostProcessing").add_variable("stress");
...
Then assemble the L2 projection system like this:
compute du/dx
phi(i)*phi(j) =3D phi(i)*du/dx
and solve it in a standard way.
This type of system will be trivially easy to solve since it is SPD=20
(just a mass matrix).
Let me know if you have any more questions.
Ben
Martin L=FCthi wrote:
>John
>
>John Peterson writes:
> > Martin L=3DFCthi writes:
> > > Is there an easy way to output calculated quantities to the GMV ou=
tp=3D
> > ut
> > > files? I want to calculate e.g. stresses (or some other quantitiy
> > > which is not a system variable), and hav it appear in the output f=
il=3D
> > e.
> > You might add it as a "dummy" system variable which is just
> > computed via a postprocessing step. Then it could be written
> > out as normal to gmv.
>
>Thanks for the answer. There is a problem with this. If I add the
>variable the beginning, the system gives a null solution (because the
>variable is not used in the element loop). Adding it after just before
>the write command results in some runtime error messages.
>
>I was thinking about using an additional vector with
>system.add_vector.
>
>Best, Martin
>
>
>
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