Re: [eigen] matrix function / exponential warnings

[ Thread Index | Date Index | More Archives ]

On Sun, 20 Jun 2010, Hauke Heibel wrote:

The issue is that the classes MatrixFunction and MatrixExponential are storing

const MatrixType& m_M;

and it seems to be expected that the MatrixType is always a
PlainObject. I am not sure whether that is really necessary. We
already have a solution to this in Eigen which means storing objects
as ei_nested<...>::type.

I think I didn't know about ei_nested when I wrote the code. As far as I remember it, I modeled it on the implementation of MatrixBase::lu() .

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.

Even when we leave the code as is, I think we need to change at least

const typename ei_eval<Derived>::type srcEvaluated = m_src.eval();


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

because ei_eval<...>::type is not necessarily equal to
Derived::PlainObject and here, you really want to pass a reference to

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.

The problem with the code you suggest is that it copies the matrix if Derived is Matrix<...> (assuming that I understand everything correctly).

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.


Mail converted by MHonArc 2.6.19+