Re: [eigen] generic argument declaration taking a matrix, vector or expression

[Bernhard Zeisl <bzeisl@xxxxxxxxxxxxxxxx>]

Christoph, thanks a lot for your hint. That solved the problem.

I agree with you that with the new declaration we lost type safety. 
Effectively A, b and x now can be of a different scalar type each.
While it's fine in our case that the function is templated over 
different scalar types, it should be required that all arguments are of 
the same type. Also it would be nice if that shows up in the interface. 
As of now, I guess this is not possible?

Best, Bernhard


On 01/10/2012 10:55 PM, Christoph Hertzberg wrote:
> On 11.01.2012 07:19, Bernhard Zeisl wrote:
> > If we understand the tutorial correctly, foo should look like
> >
> > template <typename TypeT>
> > void foo (const Eigen::MatrixBase<TypeT> &mat);
> >
> > where a const cast needs to be used to write data back to mat.
>
> Yes, the const_cast is indeed not very nice. The problem is that you 
> can't pass a temporary object (such as A.col(i)) as a non-const 
> reference (unless you use C++11's RValue references).
> Of course this bears the problem that you can also pass a const 
> Matrix<...> to foo and modify it -- which actually should be prohibited.
>
> Another problem in my opinion is that you can't easily achieve type 
> safety of foo, i.e. if you only want to allow Matrices of a certain 
> size or scalar type (but you can achieve this by static assertions).
>
> > I attached a an example, which should make more clear what we are trying
> > to achieve.
>
> You need to give every matrix a different template parameter, e.g.:
>
> template <typename Type_A, typename Type_b, typename Type_x> void
> solveLeastSquares (const Eigen::MatrixBase<Type_A> &A, const 
> Eigen::MatrixBase<Type_b> &b, Eigen::MatrixBase<Type_x> const &x_, 
> LEAST_SQUARES_METHOD method = SVD)
>
> Maybe the documentation could point that out more explicitly. 
> Especially in the quoted tutorial parameters x and y should get 
> different template arguments (in the last two examples)
>
> HTH
> Christoph