Re: specializing void MatrixBase<Derived>::makeHouseholder (Re: [eigen] Householder.h: ::min() and operator<==

[Peter <list@xxxxxxxxxxxxxxxxx>]

Dear Christoph,

Am 12.09.2016 um 11:06 schrieb Christoph Hertzberg:
> On 2016-09-11 15:41, Peter wrote:
> > [...]
> > Is there a simple way to specialize
> >
> >
> > template<typename Derived>
> > template<typename EssentialPart>
> > void MatrixBase<Derived>::makeHouseholder
> >
> > for my own type, without interfering with the Eigen files, i.e. without
> > inserting enable_if statements in the Eigen code
>
> I don't think there is an easy way.
> You could specialize this method for certain types of Derived, but you can't partially specialize methods.
> I.e., this could be possible (I did not actually try):
>   template<>
>   template<typename EssentialPart>
>   void MatrixBase<Matrix<MyType, Dynamic, Dynamic>::makeHouseholder(...)

I tried specializations like

	template<>
	void MatrixBase< TpFloat >::makeHouseholder(
	VectorBlock<TpFloat, Dynamic>& essential,
	Scalar& tau,
	RealScalar& beta) const

or
  template<>
   template<typename EssentialPart>
	void MatrixBase< TpFloat >::makeHouseholder(
	 EssentialPart& essential,
	 Scalar& tau,
	 RealScalar& beta) const

But I get >1000 lines of error messages.

> But you can't specialize like:
>   template<int rows, int cols>
>   template<typename EssentialPart>
>   void MatrixBase<Matrix<MyType, rows, cols>::makeHouseholder(...)
>
> How would you like to modify makeHouseholder?

I want to extend the handling of near-zeroes:

  if(tailSqNorm <= tol && numext::abs2(numext::imag(c0))<=tol)
  {
    tau = RealScalar(0);
    beta = numext::real(c0);
    essential.setZero();
  }


> Ideally, we should only specialize a sub-part of the function for different types (which we can do by delegating the function to a helper-struct).

I agree, I just wanted to avoid changing the Eigen-Code for simplified updating.
I try to implement a helper class here.

Best regards,
Peter