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

[Helmut Jarausch <jarausch@xxxxxxxxxxxxxxxxxxx>]

On 03/21/2013 11:44:14 AM, Christoph Hertzberg wrote:
> On 21.03.2013 11:36, 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 another very hacked solution. It requires that the data  
> layout of Matrix will not change (especially, no extra fields will be  
> introduced):
>
> EIGEN_ALIGN16
> static const double C3_data[] = {1.0/5, 3.0/10, 4.0/5, 8.0/9, 1.0,  
> 1.0};
> static const Vec6d& C3 = reinterpret_cast<const Vec6d&>(*C3_data);

That's the case for my application : matrix and vectors of weights in  
higher order Runge-Kutta methods.
Still, for a "real" matrix one would have to enter the transposed  
matrix if one likes to stay to
column ordering for efficiency.

Helmut.