sieve-dev reduce memory usage

[Shi Jin]

Hi,

As I am about to conduct production runs, the large memory cost incurred by
using the sieve data structure has become a serious obstacle for large
calculations. For example, I am planning a simulation with about 8 million
finite elements. The memory cost for the unstructured grid alone (sieve
topology and coordinates) is over 43GB. Even with 28 processes, each process
needs 1.5GB for the mesh.  Adding the field sections and matrices, it adds
up to 4.5GB per process which is not usually available on typical clusters.
Therefore, my next task is to try to reduce the memory usage of the code.
One reason for the high memory usage of the sieve data structure I guess is
the 4 levels of points in a DAG. It would cost much less if interpolation is
disabled. However, we need the edges to have second order elements. But
indeed we don't need the faces. I am wondering if it is possible to
partially enable interpolation, i.e., to have only 3 levels: vertexes, edges
and cells, without the faces.Hopefully, this may reduce the memory cost by
at least 25%. Do you think this is something already available or that can
be implemented fairly easily?

Thank you very much.

-- 
Sincerely,
Shi Jin, Ph.D.
http://www.ualberta.ca/~sjin1/
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