dolfin team mailing list archive

[Anders Logg <logg@xxxxxxxxx>]

Looks great Johan! I will get back with more comments, but here's a
thought: It seems it would be possible import FFC directly into
(py)dolfin and wrap the dolfin-swig tool suitably so that a user does
not even have to visit the command-line and import the generated
Python modules. Python should allow us to compile and import the new
modules on the fly.

/Anders


On Wed, Jan 25, 2006 at 03:35:59PM +0100, Johan Jansson wrote:
> Hi everyone,
> 
> I have implemented a new tool called (for now) dolfin-swig which I
> think is the final piece which now allows full development of
> PDE solvers in PyDOLFIN. What dolfin-swig does is automatically
> convert a (FFC-compiled) form into a Python module (using SWIG). This
> makes it possible to develop PDE solvers in Python without having to
> touch the main source tree of DOLFIN.
> 
> I will make an example using some existing forms. We can copy the
> Poisson3D, Elasticity and Stokes3D forms to some directory where we
> are doing PyDOLFIN development.
> 
> We compile the forms with FFC (the dolfin-swig format is just the
> dolfin format with un-nested classes, to help SWIG):
> 
> ffc -l dolfin-swig Poisson3D.form
> ffc -l dolfin-swig Elasticity.form
> ffc -l dolfin-swig Stokes3D.form
> 
> We use dolfin-swig to turn the forms into Python modules:
> 
> dolfin-swig Poisson3D.h
> dolfin-swig Elasticity.h
> dolfin-swig Stokes3D.h
> 
> We now have 3 new Python modules called: poisson3dform, elasticityform
> and stokes3dform.
> 
> We can now use them with PyDOLFIN:
> 
> python
> 
> >>>
> >>> from dolfin import *
> >>> mesh2D = UnitSquare(1, 1)
> >>> mesh3D = UnitCube(1, 1, 1)
> >>>
> >>> import poisson3dform
> >>> import elasticityform
> >>> import stokes3dform
> >>>
> >>> apoisson = poisson3dform.Poisson3DBilinearForm()
> >>> Apoisson = Matrix()
> >>> FEM_assemble(apoisson, Apoisson, mesh3D)
> >>>
> >>> aelasticity = elasticityform.ElasticityBilinearForm(1.0, 1.0)
> >>> Aelasticity = Matrix()
> >>> FEM_assemble(aelasticity, Aelasticity, mesh3D)
> >>>
> >>> astokes = stokes3dform.Stokes3DBilinearForm()
> >>> Astokes = Matrix()
> >>> FEM_assemble(astokes, Astokes, mesh3D)
> >>>
> 
> Then do something with the matrices.
> 
> As you can see, as long as we have a proper DOLFIN installation, we
> don't have to touch the DOLFIN source tree, we are able to work only
> with FFC and PyDOLFIN. And we can quickly and easily test forms, try
> new forms, make test cases etc.
> 
> 
> One extension of this concept is to provide a general dolfin-swig
> (right now it only works for forms) which would allow any DOLFIN-based
> code to be converted into a Python module. Then it would be possible
> to write a small piece of C++ code implementing a coefficient function
> or a boundary condition, convert it into a Python module using a
> simple tool like this, and use it in a PDE solver in PyDOLFIN. This
> would enable PDE solvers in PyDOLFIN to be exactly as efficient as
> modules developed in pure C++.
> 
> 
> I thought this would also allow run-time modification of forms. What
> we should be able to do is:
> 
> >>> apoisson = poisson3dform.Poisson3DBilinearForm()
> >>> Apoisson = Matrix()
> >>> FEM_assemble(apoisson, Apoisson, mesh3D)
> >>>
> 
> Then we discover some bug in the form perhaps, some element in the
> matrix seems wrong. So we modify it (in some other window) and
> recompile the form:
> 
> ffc -l dolfin-swig Poisson3D.form
> dolfin-swig Poisson3D.h
> 
> And reload the module:
> 
> >>> reload(poisson3dform)
> 
> This works, but it seems the signatures of the objects in the new
> module don't match the signatures in the old module, so for some
> reason the reloaded module isn't compatible with the PyDOLFIN module
> anymore (so we can't assemble the form). I'll try to find out what the
> problem is, hopefully this is just some issue in SWIG that can be
> fixed.
> 
> It's not so important though. We can just restart Python and run our
> program again, I would say this is usually how development is done
> anyway. But it can be important in the future, perhaps when a GUI is
> wrapped around everything, then we probably don't want to break
> run-time.
> 
> 
> I will experiment and test PyDOLFIN with this new tool over the next
> few weeks, and then hopefully it can be established as a real
> (practical, efficient) environment for doing PDE solver development
> in.
> 
>   Johan
> 
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> 

-- 
Anders Logg
Research Assistant Professor
Toyota Technological Institute at Chicago
http://www.tti-c.org/logg/