Chuks,
I am trying to compute a quantify in my finite element code that
requires integrating along a line, starting from a reference cell. With
one processor, this is fine. However, with multiple processors, there is
the chance that due to element partitioning, the line extends into the
region of cells owned by other processors. One option for me is to
increase the size of the ghost cells so that the line will always be in
a region of cells owned by the same processor. However, dealii ghost
cell size is always one.
Yes. But even if there was a way to extend the ghost region, you may
have lines that extend across the entire domain and in that case you may
end up with a situation where one processor would have to know *every*
cell. This is not scalable. So this does not work.
What you will have to do is this:
* For each line along which you have to compute something, make sure
that *each* processor knows about it.
* Let each processor integrate over that part of the line that
intersects the cells that this processor owns. That set may be zero, in
which case the the part of the integral that this processor computes is
simply zero.
* Add up the contributions of all processors.
1. From gauss point of reference cell, project to a new location along
the line
2. Find cell containing the new location (cell may or may not be within
the same partition).
3. Compute quantities at the new location using finite element solutions
4. Continue projection along line and repeat step 2 again.
This is a reasonable algorithm. Execute it on *all* processors and in
step 2, if the point is not found in a cell that the current processor
owns, just ignore the point -- one processor (exactly one!) will own the
surrounding cell, and if you add up the result over all processors, you
will get all necessary contributions.
Best
W.
--
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Wolfgang Bangerth email: [email protected]
www: http://www.math.colostate.edu/~bangerth/
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