Re: [eigen] Serious conflict between Dynamic and -1 in Diagonal<>

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

On 07/10/2012 10:34:12 AM, Gael Guennebaud wrote:
> Hi,
>
> as pointed out in this thread:
>
> http://forum.kde.org/viewtopic.php?f=74&t=106803
>
> there is a serious issue in the Diagonal<Expression, DiagIndex> class.
> Recall that Diagonal<> represents an expression of the diagonal
> (DiagIndex==0), a super-diagonal (DiagIndex>0) or a sub-diagonal
> (DiagIndex<0).
>
> Of course, one can also set DiagIndex to Dynamic to pick a given
> super/sub diagonal at runtime. The problem is that since Dynamic==-1,
> we cannot distinguish between the first sub-diagonal (DiagIndex==-1)
> and a runtime selected diagonal.
>
> Since changing the value of Dynamic is not an option, I propose to add
> a special enum for this use case, like RuntimeDiagIndex or
> DynamicDiagIndex that would be set to a very big value.
>
> Opinion? better solution?

For readability I'd prefer something like
Diagonal<Expression, Offset(-1)>

or

Diagonal<Expression, Offset<-1> >

Helmut.