[aspect-devel] A follow question from the webinar ...

[Rene Gassmoeller]

Hi John,

let me copy this mail to the developer list, because it is a reasonable
question, and others might profit from the discussion as well.

What you propose is already possible, just not the default way. You can
access the particles from the outside (see
source/postprocess/visualization/particle_count.cc for an example), and
you can either implement your own averaging scheme, or ask the particle
world for the selected interpolator (World::get_interpolator()).

That being said, I am skeptical you can do better that way for two reasons:
- The memory requirement of ASPECT mainly comes from the space needed
for the matrices, but if you select to advect a compositional field by
particles then we do not assemble or reserve the space for this block of
the system matrix (that was a problem in the beginning but was fixed a
while back by @klass4kayaker in pull request #1155). The solution vector
itself should not need much memory.
- The reason we interpolate the properties once and then access them
like a compositional field is that the interpolation is expensive
compared to the evaluation of this field at a certain position. If you
directly access the particle data you will need to do the interpolation
many more times (e.g. once for the assembly of the Stokes system, once
for other advection systems, once for the postprocessors, ...). Maybe it
can be similar in speed if the interpolation is fast, but I doubt it can
be faster.

Feel free to give it a try, but I would not expect many benefits (except
you do not need to rely on the finite element discretization of the
compositional field, but then you introduce that again, because the
velocity you are solving for is discretized the same way).

Cheers,
Rene

On 11/10/2016 05:28 PM, John Naliboff wrote:
> Hi Rene,
>
> I actually have a follow up question from the talk.  To reduce memory
> requirements, would it be reasonable in the future to have material
> models that access particle information directly rather than through a
> compositional field?
>
> In this scenario, a particle interpolation scheme would be called
> every time the material model needs particle information interpolated
> to a quadrature point.
>
> I suppose this could noticeably increase the computational time if one
> has to do lots on non-linear iterations.   Trade-off between
> computational time and memory requirements.  For 3D models, I imagine
> the memory requirements may be a bigger issue.
>
> Gerry Puckett and I have been discussing this after running into
> memory issues with 3D models.
>
> Anyhow, thanks again for the great talk!
>
> Cheers,
> John
>