[petsc-dev] Tao unusable from complex??

[Stefano Zampini]

Il giorno mer 12 dic 2018 alle ore 18:06 Dener, Alp <adener at anl.gov> ha
scritto:

> Hi Stefano,
>
> I can’t really speak to why the entirety of TAO is disabled in complex
> builds. Todd can probably offer historical insight to the reason(s).
>
> However, we do have some methods in TAO that are not tested or guaranteed
> to be correct for complex-valued objective functions.
>

As far as I understands, TAO is clear in requiring  real objective
functions, having PetscReal on the prototype for the callback

The limited-memory quasi-Newton codes, for instance, currently only
> construct the approximate Hessian for the real part of the function and do
> not generate step directions in the complex part. I also don’t know whether
> any of the CG methods or line searches require any modifications to be
> correct in complex builds either.
>
> In your itemized list, I agree that at minimum we should be supporting #3
> even if TAO itself does not work correctly for complex-valued functions.
>
> In the meantime, TAO can test real gradients or Hessians internally with
> `-tao_test_gradient` or `-tao_test_hessian`. Or you can also call
> `TaoTestHessian()` too. It’s a finite-difference test though, and not a
> complex-step test.
>
> ——
> *Alp Dener*
> Argonne National Laboratory
> https://www.anl.gov/profile/alp-dener
>
>
> On Dec 12, 2018, at 8:23 AM, Stefano Zampini via petsc-dev <
> petsc-dev at mcs.anl.gov> wrote:
>
> If I compile PETSc with complex support, all of the TAO methods are not
> registered.
> Fare enough? not really, I can imagine at least three valid reasons to use
> those
>
> 1) I want to check that my code works for complex builds, even if I have
> pure real function evaluations. I may need complex support in other parts
> or the code (not when using TAO), or I just want to be a diligent PETSc
> developer
> 2) I want to test REAL gradients or Hessians using built-in capability,
> instead of writing my own
> 3) I want to use the complex differentiation trick to compute REAL
> gradients
>
> Last time I checked, at least option 2) was available; However, from
> commit 5921d7004dad83427f45468906667b100d2e2b6e, no Tao methods are
> registered when PETSC_USE_COMPLEX is defined, and code like the one below
> fail at runtime:
>
> TaoCreate()
> TaoSetFromOption()
> TaoSetObjectiveRoutine()
> TaoTestGradient()
>
> [0]PETSC ERROR: Unknown type. Check for miss-spelling or missing package:
> http://www.mcs.anl.gov/petsc/documentation/installation.html#external
> [0]PETSC ERROR: Unable to find requested Tao type lmvm
>
>
> --
> Stefano
>
>
>

-- 
Stefano
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