Re: [eigen] Eigen Types as Parameters for Functions

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 26.01.2012 14:33, Benoit Jacob wrote:
> 2012/1/26 Christian Seiler<christian@xxxxxxxx>:
> >   - subclass of MatrixBase, i.e. can be used inside the function like a
> >    Matrix object
> >   - has private members containing the above-mentioned bits of
> >    information (pointer to first element, dimension, ...)
> >   - can be implicitly converetd to from any compatible MatrixBase (i.e.
> >    foo(mat) and foo(mat.block(...)) can be used directly)
>
> Just note that this is only possible for those matrix expressions
> whose coefficients are stored in memory with a simple enough layout
> that can be described in terms of strides. That is what we call a
> "Direct Access" matrix expression; the test is ExpressionType::Flags&
> DirectAccessBit.

Yes, and I would say this would be the main application, if you have 
complicated-enough functions (i.e. where you don't really bother about 
evaluating expressions to a temporary if required).
And more importantly, when having parameters that are actually output 
parameters, you are more or less stuck to direct access types anyway -- 
and this is a very important point, where currently const-correctness is 
ignored (almost) entirely.

> With that said, yes, we have been considering doing this, that's bug 58:
> http://eigen.tuxfamily.org/bz/show_bug.cgi?id=58
>
> If someone wants to do this and needs mentoring, I should find time to
> do at least that mentoring.

I'd be interested at least to join the "specification committee" ;)

Christoph


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Dipl.-Inf. Christoph Hertzberg
Cartesium 0.051
Universität Bremen
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28359 Bremen

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