[firedrake] parallel weirdness

[Lawrence Mitchell]

On 18 Nov 2014, at 21:35, Hiroe Yamazaki <h.yamazaki at imperial.ac.uk> wrote:

> Hi Lawrence,
> 
> you can reproduce the problem by runing test_linear.py at
> bitbucket.org/colinjcotter/slicemodels/branch/periodic_parallel. With
> 1 and 2 cores, it gives different results.
> 
> The code Colin is describing with line numbers is an old-version of
> slicemodels.py, which is found here:
> 
> https://gist.github.com/anonymous/c308131558ff54fec9c4
> 
> In this version I added this term
> 
> - (-dt*div(w)*pbar)*dx
> 
> in line 270, which was previously added to the RHS in line 139.
> With this change, the parallelization problem seemed to be fixed and I
> got the same results with 1 and 2 cores, but but it makes no sense to
> us.

I cannot reproduce this problem with the current HEAD of that branch (6ce1ffb02).  The output vtus look the same in the eyeball norm, and once I fix the printing of the deltap (Colin, in parallel you can't look at the sum of the local entries.  Do function.dat.norm to get the l2 norm or norm(function) for the L2 norm).  In particular, if I specify jacobi PCs for /all/ solvers I get basically identical values in serial and parallel (up to solver tolerance)

So I don't really know where to look.  Can you give a precise sequence of steps for me to follow to reproduce the problem and observe it?

Lawrence
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