[petsc-users] FEM 101

[Justin Pogacnik]

Yep, thanks for that Matt. I'll start playing around with the PetscFEIntegrate routines in C++. Is there any plan to make those accessible in F90? Also, I'm not seeing DMPlexIntegrateResidual.

Thanks for the help,

Justin
________________________________
From: Matthew Knepley [knepley at gmail.com]
Sent: Tuesday, March 31, 2015 5:14 PM
To: Justin Pogacnik
Cc: petsc-users at mcs.anl.gov
Subject: Re: [petsc-users] FEM 101

On Mon, Mar 30, 2015 at 4:39 PM, Justin Pogacnik <j.pogacnik at auckland.ac.nz<mailto:j.pogacnik at auckland.ac.nz>> wrote:
Hello,

I'm beginning to write a finite element solid mechanics code in F90 and am having some problems getting started with finite element basics within Petsc. I'm using an unstructured grid and the DMPlex class and able to access most of the mesh information required for FE numerical integration. I've used PetscFECreateDefault and have found the quadrature point locations/data. I'm trying to determine how to find the values of standard trilinear basis functions and their derivatives at the element quadrature points and then to perform the integration on the element. Can anyone advise what the proper routines are that I should call? It's possible that I'm way off target. I've seen "PetscFEGetBasisSpace", but I'm unsure what to do with the resulting output space. I've also seen the PetscFEIntegrate routines, but unsure how their intended to be used and don't see any fortran wrappers.

I hope this question is clear. Please let me know if you require more information. I appreciate any help and guidance that anyone can offer.

Here is the plain vanilla integration routine:

  https://bitbucket.org/petsc/petsc/src/1c9d18e7633f5b782021dca6d8727de2838ee261/src/dm/dt/interface/dtfe.c?at=master#cl-3380

which is an implementation of PetscFEIntegrate(). The idea is that this integrates a bunch of elements, and then there is an outer
loop over the whole mesh, which is currently DMPlexIntegrateResidual(). Unfortunately, this function also does a bunch of other
stuff, and right now I do not see how to simplify it.

Does this make sense?

  Thanks,

     Matt

Many thanks,

Justin



--
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead.
-- Norbert Wiener
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