[firedrake] Issues with LMA of vertical derivative on extruded meshes

[Lawrence Mitchell]

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On 06/01/15 08:52, Eike Mueller wrote:
> Hi Lawrence,
> 
> thanks for the explanation, so my understanding is that in general
> PyOP2 is not aware of the COFFEE optimisation, and the wrapper code
> that is generated in my PyOP2 parloop can’t handle the padding.

Yes, that's right.  You can follow this issue
https://github.com/coneoproject/COFFEE/issues/14 to see if anything
will change.  I hope so, since it's not a very nice model.

> Since I call a PyOP2 parloop directly, I don’t have any control
> over the wrapper code and at the moment it sounds like the only
> thing I can do is switch off the COFFEE optimisation (which, I
> suppose, has implications everwhere in the code, so I really
> shouldn’t do this).

You can do the following in build_lma:

def build_lma(...):
    parameters["coffee"]["O2"] = False
    existing_code
    parameters["coffee"]["O2"] = True


That way the optimisations are only switched off for that one section.

> Isn’t then there a problem with all PyOP2 parloops, and are you
> going to do something about this?

So the problem is that you're doing something that isn't explicitly
supported by the PyOP2 data model: using a Kernel designed for
assembling into a Mat to assemble into a Dat.  It happens to work in
some cases.

I think it is probably useful to properly support a "build_lma_matrix"
style abstraction, but I haven't thought properly about how to do it
right.

Lawrence
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