Re: [eigen] [FAQ] how to have an initialized static Matrix

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

On 03/21/2013 11:36:24 AM, Christoph Hertzberg wrote:
> On 21.03.2013 10:30, Helmut Jarausch wrote:
> > unfortunately, Eigen's elegant initialization is an expression.
> >
> > Is there an "elegant" solution for this ugly code (within a function)
> >
> >
> >    static double _C[6] = { 1.0 / 5, 3.0 / 10, 4.0 / 5, 8.0 / 9, 1.0,  
> > 1.0 };
> >    static const Eigen::Map<Eigen::Matrix<double,6,1>,0>  
> > C((double*)_C);
>
> I found these three solutions:
>
> typedef Eigen::Matrix<double, 6, 1> Vec6d; // for brevity
>
> // Comma-initializer:
> static const Vec6d C0 =
>     (Vec6d() << 1.0/5, 3.0/10, 4.0/5, 8.0/9, 1.0, 1.0).finished();

I didn't think of this myself. I like it. Especially, when initializing  
matrices
with more then one row/column this versions shows the coefficients as  
we mathematicians
write them down, i.e. row wise.

> // Initialize from const data
> static const double C1_data[] = {1.0/5, 3.0/10, 4.0/5, 8.0/9, 1.0,  
> 1.0};
> static const Vec6d C1(C1_data);
>
> // Map to aligned const data:
> EIGEN_ALIGN16
> static const double C2_data[] = {1.0/5, 3.0/10, 4.0/5, 8.0/9, 1.0,  
> 1.0};
> static const Eigen::Map<const Vec6d, Eigen::Aligned> C2(C2_data);
>
> The first two most likely will have a one-time copy overhead, the  
> third might have a very minor overhead when using it (e.g. if you  
> pass it by reference, two pointers need to be dereferenced instead of  
> one).
>
>
> > What about Matrix with a constructor taking an initializer_list ?
>
> That would be possible with C++11 only (still worth thinking about).

Yes, please. It's only a few additional constructors which could be  
generated only if
__cplusplus is 201103L or beyond.

But, if we are at it, what about move constructors or move assignment  
operators,
Helmut.