-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 23.07.2010 20:33, Kristian Ølgaard wrote: > On 23 July 2010 13:30, Florian Rathgeber > <[email protected]> wrote: > On 23.07.2010 14:22, Kristian Ølgaard wrote: >>>> On 23 July 2010 13:02, Florian Rathgeber >>>> <[email protected]> wrote: >>>> I guess I haven't made my point very clear. The demo you gave is a good >>>> example of what's currently possible and where the limit is I think. >>>> >>>> Say you take dolfin/demo/pde/spatial-coordinates/cpp and want to >>>> restrict the source term f to only a circle in the center of the domain. >>>> How would you do that? I wouldn't know another way than a conditional >>>> and I couldn't find a way to get that working with FFC. >>>> >>>>> Now it makes more sense, I think you would need a conditional indeed. >>>> >>>> I was not talking about constants, but about expressions that are not >>>> uniform over the whole domain, should have made that more clear. >>>> >>>> Florian >>>> >>>> On 23.07.2010 13:51, Kristian Ølgaard wrote: >>>>>>> On 23 July 2010 12:40, Florian Rathgeber >>>>>>> <[email protected]> wrote: >>>>>>> Hi, >>>>>>> >>>>>>> Profiling DOLFIN assembly shows that for forms with many coefficients or >>>>>>> computationally expensive expressions assigned to coefficients, a great >>>>>>> deal of the whole assembly is spent in expression evaluation. >>>>>>> >>>>>>> An idea I wanted to investigate was giving an expresssion in UFL and >>>>>>> have FFC generate corresponding code to evaluate it inline during tensor >>>>>>> tabulation. That should have the potential of eliminating some of the >>>>>>> overhead. >>>>>>> >>>>>>> However, currently that is only possible within very limited bounds. FFC >>>>>>> does not yet support UFL conditionals, which essentially limits possible >>>>>>> expressions to depend on coordinates only and be the same over the whole >>>>>>> domain (which is not very useful for most form coefficients, e.g. source >>>>>>> terms). >>>>>>> >>>>>>>> Did you have a look at the dolfin/demo/pde/spatial-coordinates/cpp >>>>>>>> demo? It is essentially the dolfin/demo/pde/poisson/cpp demo but it >>>>>>>> uses source and boundary terms defined using coordinates and is not >>>>>>>> the same over the whole domain (I don't really get your point here). >>>>>>>> The coordinates are defined as the coordinates of the current >>>>>>>> integration point located on the current cell which is being >>>>>>>> integrated. Have a look at the generated code, then it might be >>>>>>>> clearer what's going on. >>>>>>> >>>>>>>> Kristian >>>>>>> >>>>>>> This brings me to my questions: >>>>>>> 1) Do you see a reasonable chance for speeding up assembly in the way >>>>>>> described? >>>>>>> 2) Is my assessement correct? Or do I miss some capabilities of FFC that >>>>>>> support my use case? >>>>>>> 3) Since UFL basically support arbitrary python syntax, would it be >>>>>>> reasonable to support translation for user-defined Expressions given in >>>>>>> python (either overloading eval in a class defived from Expression or >>>>>>> passing C++ code to the SWIG constructor of Expression)? FFC would >>>>>>> generate code to evaluate these Expressions inline during tensor >>>>>>> tabulation. That would of course require the Expression to be stateless >>>>>>> and have not input other than the coordinates. But at least it would >>>>>>> provide much more flexibility and also consistency with the DOLFIN >>>>>>> interface in general >>>> >>>>> I think it sounds complicated, much better to defined the function >>>>> directly in terms of coordinates. >>>> >>>>>>> (sidenote: it is possible to specify Expressions in this way in UFL, but >>>>>>> they are treated just like Coefficients by FFC) >>>> >>>>> I don't think this is the case, it is possible in the Python interface >>>>> to DOLFIN, but not in UFL. > > You are right, it is not in the UFL specification. It is technically > possible with FFC though. I passed the example UFL file I gave to FFC > and it was accepted, however the generated code was the very same as if > I had just written > >> No, it is technically possible in PyDolfin. Not UFL or FFC >> Anyway, I've implemented support for conditionals see if it works. >> (dolfin/demo/pde/conditional) >> I only tested '<' so far but the other operators should work the same way. > >> Kristian
Thank you for implementing that and sorry for not coming back to this earlier. As far as I can see, it is only implemented for quadrature. Is there a fundamental problem that would inhibit implementing it for tensor representation as well? Florian -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.12 (MingW32) iEYEARECAAYFAkxWtSYACgkQ8Z6llsctAxZwpACfaAKeewvmEknig7ySe9nxGaM1 2ZwAn07Mkka+BMcvbuVlWMMV1iVRF0QP =0E1w -----END PGP SIGNATURE-----
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