[aspect-devel] The fast way to grab the radius of every interior sphere in the domain and some MPI questions

[Shangxin Liu]

Hi;

I'm now making a new plugin into the postprocess directory to compute geoid
anomaly. The code has been finished but it needs some further modification
to run in parallel. To realize this, I run into these two problems:

1. The geoid computation needs the integral of the density anomaly from CMB
to surface. For now, I do the integral based on cells. So to get all the
radii of the internal spheres, the code loops over all of the cells and get
the radius of each cell's upper face and push_back the radius into a vector
after removing the same values from the cell faces at the same depth. But I
suppose this solution is not so elegant and also will not work in the
multiple MPI processors since each processor will only cover part of the
domain. So is there a fast way in deal.ii/ASPECT to directly grab all the
radii of the spheres determined by the cell faces within the domain?

2. In the spherical harmonic coefficients computation, I need to evaluate
the values at each grid points I created prepared for sphere integral from
the output values at the center of each cell face. My current solution is
to loop over all the sphere cells and find the closest cell face midpoint
to the grid point (nearest point interpolation). But since each processor
will only cover part of the domain so I also need to compare among all the
processors to find the closest point and the corresponding density
anomaly/topo values at that point. I notice that there is a
Utilities::MPI::max/min command can compare among different processors. But
my purpose is not only to get the closet distance, but also need to know
which processor provide this closest cell face midpoint and the
corresponding location of this closet cell midpoint hence to get
the density anomaly/topo there. Are there any MPI commands in
deal.ii/ASPECT to realize this?

Best,
Shangxin
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