Excellent input. I wasn't thinking that way at all, but I see no reason to
not move in that direction...
From: Roy Stogner [mailto:roystgnr@...]
Sent: Friday, March 18, 2005 4:39 PM
To: KIRK, BENJAMIN (JSC-EG) (NASA)
Subject: Re: updated ex3
On Fri, 18 Mar 2005, KIRK, BENJAMIN (JSC-EG) (NASA) wrote:
> I've attached an updated ex3.C showing how you can derive from System
> and implement user_assembly() to assemble your system. Similarly, you
> can implement user_initialization() to perform any user-defined
> initialization you want.
> Clearly this makes it easier to get data to the assembly routines.
It's an improvement over passing function pointers, but I'm sure we can
abstract away more. In that whole assembly function, how many lines are
problem specific? Just the equations themselves; everything before
"Fe.resize()" and everything after the boundary conditions loop is
If we make that boilerplate a standard function, and let the user override
just a "cell_assembly" function that the standard assembly function calls
once per active element, then not only does it make user code shorter but it
gives us more options. Matrix-free methods could be turned on/off with a
switch; residual-based error indicators could call the same cell_assembly
function (after "faking" new boundary sides); libMesh code could choose to
preeliminate interior degrees of freedom... it would even make hp adaptivity
easier to write in the future, by moving the "all cells are the same FE
type" assumption into libMesh code, where it can then be weakened without
changing user code.
The only concern I have is efficiency, but I doubt a function call (even one
that may need a lot of arguments) is going to be much worse than the FE
reinit and triply nested loops that already needs to be done per cell.