[petsc-dev] coding style

[Jed Brown]

"Oxberry, Geoffrey Malcolm" <oxberry1 at llnl.gov> writes:

> I realize this point was brought up earlier, but doesn’t this
> discussion still assume that evaluating g at zero is defined and makes
> sense? Though I see the appeal in this design, I’m not sure it will
> necessarily work in practice. For instance, we definitely have
> formulations that involve terms like sqrt(x), which isn’t
> differentiable at zero, and would break this interface. (We would
> bound the feasible set away from zero, so the optimization algorithm
> should still work.)

Isn't the context of this particular comment that the user claims their
model is quadratic?  Of course evaluating at 0 has no special meaning
for a general nonlinear model.

>> On Aug 18, 2016, at 11:02 AM, Munson, Todd <tmunson at mcs.anl.gov> wrote:
>> 
>>> 
>>> People are free to use MatShell to create a "matrix" that is
>>> actually a nonlinear operator.  Solvers won't work properly if it's
>>> not, but that's their problem.
>> 
>> The quadratic programming solvers in our case will happily go and
>> tell you it solved the problem...however, the problem it solved uses
>> 
>>  c = grad[g(0)] H = hess[g(0)]
>> 
>> I'd be happier if the solver barfed and told the user to select a
>> method appropriate for their real problem -- it it truly is nonlinear
>> -- rather than going off and solving the wrong problem, which is what
>> is done today.
>> 
>> Todd.
>> 
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