[petsc-dev] getting ready for PETSc release

[Jed Brown]

Matthew Knepley <knepley at gmail.com> writes:
>> This is awfully prime real estate in the namespace to be placing
>> functions that run at quadrature points, do not have context arguments,
>> cannot share results of a material model, is somewhat specific to finite
>> elements, does not support Riemann solvers, characteristic
>> reconstruction, general boundary conditions, etc.
>>
>
> I gave my reasons for excluding context argument from the bottom level
> functions. The context appears at the next level up, so that can be
> replaced if you do not like the quadrature-level interface.

And yet the quadrature interface is what occupies that prime namespace.
Other uses of unadorned wording like "Residual" (well, everything else
uses Function, though I would use Residual if starting anew) and
"Jacobian" are in places that do not even assume a PDE or variational
problem, let alone a very specific class of discretizations.

>> I don't think PETSc should be in the business of creating a Framework.
>> To be honest, I would rather see functionality like this provided in an
>> external library so that it isn't confused with the more general-purpose
>
> I think this argument can be made about anything on top of Vec and
> Mat, like TS. The real criterion we use to decide these things is how
> useful it would be for the majority of PETSc users. I think this is a
> hands-down win there.

Keep in mind that (a) many PETSc users already use a discretization
package so they couldn't care less about PetscProblem, and (b) many
users that call PETSc directly have rather exotic discretizations or are
not solving PDEs so PetscProblem is of no use for them.

TS works on a semi-discrete form and assumes nothing about the equation
(such as spatial discretization, if applicable).  The interfaces that
offer something more specific are namespaced accordingly, e.g.,
DMDATSSetIFunctionLocal().  I would have less issue with
DMMattsCoolDiscretizationTSSetIFunctionVolumetricQuadrature (which may
or may not be "in scope"), but PetscProblemSetResidual is downright
pretentious.
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