Re: [eigen] Indexes: why signed instead of unsigned?

[Mark Borgerding <mark@xxxxxxxxxxxxxx>]

Is there any reason why sparse matrices backed by distributed storage 
need to use the same indexing integer data type as the more common dense 
storage in memory?

Beware bending a design to meet the edge case. 



Benoit Jacob wrote:
> Note: the distribute storage case is an example where one might want
> 64bit indices even if the CPU architecture is 32bit. Indeed, since the
> array doesn't need anymore to fit in RAM...
>
> So it's an example where ptrdiff_t may not be the right choice.
>
> Benoit
>
> 2010/5/11 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
>   
> > grrr, i had forgotten but a while ago someone inquired about the
> > possibility to use eigen with distributed storage, and we took that
> > into account when doing the big class-hierarchy-refactorings, to
> > ensure it's possible to plug in a new storage system, see
> > StorageKind... so it would be a bit too bad to restrict the indices
> > types to int.
> >
> > This actually suggests that no matter what the default is, the indices
> > type should be something that the Storage can control. This would also
> > allow Sparse matrices to use different index types. We could make it a
> > typedef in ei_traits, that is propagated to nested expressions, ...
> >
> > Gael, what's your opinion?
> >
> > Benoit
> >
> > 2010/5/11 Benoit Jacob <jacob.benoit.1@xxxxxxxxx>:
> >     
> > > 2010/5/11 Rui Maciel <rui.maciel@xxxxxxxxx>:
> > >       
> > > > On 11 May 2010 16:47, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
> > > >         
> > > > > I just had a diabolic idea, if we agree that bigger-than-2^31-support
> > > > > is not a top priority and will at most be used by relatively few
> > > > > people, then we can keep things unchanged for now, so keep 'int' in
> > > > > Eigen 3.0, and later on, when actual people actually need it (perhaps
> > > > > in eigen 3.45), add a non-default compile-time option
> > > > > EIGEN_USE_LONG_INDICES. Such an option would then break the ABI of
> > > > > Eigen classes, so it couldn't become default.
> > > > >
> > > > > Question - is BLAS/LAPACK using int or ptrdiff_t ?
> > > > >
> > > > > Benoit
> > > > >           
> > > > As this move will break the ABI then why not implement it right on the
> > > > 3.0 release instead of pushing it to a point release in the future?
> > > >         
> > > Because we've a lot on our plates already now.
> > >
> > > Benoit
> > >
> > >       
> > > > Rui Maciel
> > > >
> > > >
> > > >
> > > >         
>
>