Re: [eigen] Re: recent improvements in the products

[Benoit Jacob <jacob.benoit.1@xxxxxxxxx>]

2009/7/30 Gael Guennebaud <gael.guennebaud@xxxxxxxxx>:
> On Tue, Jul 28, 2009 at 8:24 AM, Benoit Jacob <jacob.benoit.1@xxxxxxxxx> wrote:
>> > * currently we can only solve for  X = M^1 * Y, but we also need X = Y *
>> > M^-1. Implementation wise we just have to transpose everything, so actually,
>> > the user can probably already do:
>> >    m1.transpose().triangularView<UpperTriangular>(m2.transpose());
>> >  but that's not very nice API wise. The only solution I see is to add an
>> > option to TriangularView::solveInPlace(), e.g., solveInPlace(m2, Right);
>>
>> Yes and then i'd call that OnTheRight.
>
> ok, finally it turns out that this "side" parameter should be a
> compile time parameter, otherwise we would have:
>
> if(side==OnTheRight)
>  call version_1
> else
>  call version_2
>
> that means for a template library twice the compilation time. So:
> 1 - it could be a template parameter of the solve function with
> overloads for mimic a default parameter:
>
>    m.triangularView<UnitUpperTriangular>().solveInPlace<OnTheRight>(x);
>
> 2 - or we can add new solve functions:
>
>    m.triangularView<UnitUpperTriangular>().solveInPlaceOnTheRight(x);
>
> 3 - or we can define OnTheRight/OnTheLeft as instances of different
> types allowing:
>
>    m.triangularView<UnitUpperTriangular>().solveInPlace(x, OnTheRight);
>
>
> any preference ?

I think I prefer 1 or 2, but not 3. I would reserve 3 for cases where
the special value replaces what can otherwise be a normal parameter:
see resize(int,int) and NoChange.

Benoit