Re: [eigen] matrix function / exponential warnings

[Hauke Heibel <hauke.heibel@xxxxxxxxxxxxxx>]

On Sun, Jun 20, 2010 at 5:16 PM, Jitse Niesen <jitse@xxxxxxxxxxxxxxxxx> wrote:
> What warnings do you get? I don't remember that I got any, so I guess it's
> MS specific. I think that MatrixBase::fullPivLu() does something very
> similar, so I'm interested why you don't get warnings there.

I got this one:
  warning C4181: qualifier applied to reference type; ignored

It is happening when you do e.g. something like this:
  typedef int& IntRef;
  int a = 5;
  const IntRef b = a;

So nothing to worry about though I really want to have a green
dashboard for 3.0.

> I thought that eval() always returns either a PlainObject or a constant
> reference to a PlainObject. That's what the comment "ei_plain_matrix_type:
> the difference from ei_eval is that ei_plain_matrix_type is always a plain
> matrix type,whereas ei_eval is a const reference in the case of a matrix" in
> XprHelper.h suggests to me.

ei_eval<T> is either a

 PlainObject = ei_eval<T>::type

or it is a

 T const&

or even a

 T

So in case you really want to store your temporary, I would just do
this (which I did in my patch)

const typename Derived::PlainObject srcEvaluated = m_src.eval();

>> Any comments? Is there a particular reason why ei_nested<...>::type
>> should not be working out of the box?
>
> I don't know what n should be in ei_nested<...> . It should definitely be
> high because computing matrix functions is very expensive. In fact, I
> thought that the argument of matrix functions should always be evaluated in
> situations like (matrixA+matrixB).exp() onless the argument is a matrix as
> in matrixA.exp(), in which case there is nothing to evaluate. This is
> exactly what eval() is doing.

Yes, you may be totally right. I think it does not make much sense to
go any further. Even though I added right now ei_nested, it should
change pretty much nothing because ei_nested<PlainObject> is in fact
"PlainObject const&".

- Hauke