[petsc-users] one compilation error in PETSc-dev with enabling GPU and complex number

[Jack Poulson]

Barry,

Believe me, I apologize if it came across as me trying to dump something
else on your plates. I was simply trying to point out some shortcomings of
standard approaches to complex numbers.

I know that PETSc supports quad precision for real numbers, but it seems
that there isn't yet a good way to do so for the complex case, as it would
require a custom complex class. If not, please let me know!

Jack

On Tue, Feb 7, 2012 at 1:26 PM, Barry Smith <bsmith at mcs.anl.gov> wrote:

>
>   Jack,
>
>    PetscScalar is defined in petscmath.h to be one of several things:
>
> typedef std::complex<float> PetscScalar;
> typedef std::complex<double> PetscScalar;
> typedef float complex PetscScalar;
> typedef double complex PetscScalar;
> typedef float PetscScalar;
> typedef double PetscScalar;
> typedef __float128 PetscScalar;
>
> Matt's point is that WE (the guys hacking on PETSc everyday) are not going
> to add other possibilities for cusp and complex at this point in time. We
> simply don't have the time/reason to add all this functionality now.  If
> recursader wants that functionality he is free to hack the code and add it;
> if he does it in a clean way that he can provide patches then we will put
> the patches into petsc-dev.  We simply don't have the resources to add all
> stuff to PETSc that anyone wants anytime and we have to focus on adding
> functionality that is commonly needed and will be widely used (especially
> within DOE).
>
>   Barry
>
>
>
> On Feb 7, 2012, at 12:10 PM, Jack Poulson wrote:
>
> > On Tue, Feb 7, 2012 at 11:29 AM, Matthew Knepley <knepley at gmail.com>
> wrote:
> > On Tue, Feb 7, 2012 at 11:20 AM, recrusader <recrusader at gmail.com>
> wrote:
> > Whether is it possible to find an efficient mechanism to do the
> conversion between std::complex and cusp::complex when the conversion is
> necessary.
> >
> > That does not matter. This is a compile error. We are not going to
> change this right now, and it seems like you are not going
> > make the necessary changes, so I would say that complex numbers are not
> supported with our GPU code right now. The
> > change would involve using cusp::complex for PetscScalar, and I am not
> sure how much work that would entail.
> >
> >    Matt
> >
> > Matt,
> >
> > You might be interested to hear that the C++03 standard states that "The
> effect of instantiating the template complex for any type other than float,
> double or long double is unspecified". Thus, complex quad precision with it
> is probably a bad idea and, if I'm not mistaken, the standard does not
> state that the class must store data in the form
> >
> > double real, imag;
> >
> > so this could potentially break interfaces (e.g., to BLAS or LAPACK).
> Maybe it would be worthwhile to avoid usage of std::complex and
> simultaneously fix the compatibility issue with cusp::complex. I recently
> ripped std::complex out of Elemental for the above reasons.
> >
> > Jack
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20120207/9daa3753/attachment-0001.htm>