Re: [eigen] unpleasant surprise mit math functions

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

On 09/26/2012 06:43:10 PM, rupp@xxxxxxxxxxxxxxxx wrote:
> Hi Helmut,
>
> just out of curiosity:
> which unified behavior do you expect for exp(A), sin(A) and cos(A),  
> with A being a dense matrix? If you want it to act on each entry  
> separately, then the result of exp(A) is probably not what a  
> significant number of people may expect. However, using a power  
> series expansion for exp, sin and cos is clearly not equivalent to  
> sin(t.array())...

There are 2 papers title "19 )(new) dubious ways to compute the matrix  
exponential".
Therefore, a general package like Eigen shouldn't even try to compute  
the "matrix versions".

Furthermore, I have never applied a transcendental function to a  
general matrix componentwise
but only to vectors. So, for me, it would best if Eigen would allow  
mathematical functions on vectors only.
By using Eigen::Map one could interprete a general matrix as one long  
vector in the rare cases where one wants this
functionality for matrices.

Helmut.