Re: [eigen] Recursion and block matrices

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 27.08.2012 19:33, Norman Goldstein wrote:
> I haven't been able to figure out how to write a routine that calls
> itself recursively
> with successively smaller sub-blocks of the original matrix.  Here is a
> simple example,

With the current stable branch this is not possible, because this would 
possibly generate infinitely many template instanciations. See also:
http://eigen.tuxfamily.org/bz/show_bug.cgi?id=408
There is an experimental solution here:
http://eigen.tuxfamily.org/bz/show_bug.cgi?id=481.


> [...]
>
> template< class Derived >
> void incr( const DenseBase< Derived >& mat )
> {
>    DenseBase< Derived >& matV =
>      const_cast< DenseBase< Derived >& >( mat );
> [...]
>    {
>      incr( mat.bottomRightCorner( mat.rows() - 1,
>                                                       mat.cols() - 1 ) );

Your problem here, however, is that mat is const, so 
mat.bottomRightCorner(...) is a Block<const ...> and that inner const is 
not removed by a const_cast. If you do matV.bottomRightCorner(...) 
instead, you should get to the problem above ^^.

Btw:
If you just do tail recursion, you don't need to do recursion at all, 
just do sth like this:

template<class Derived>
void incr(const DenseBase<Derived>& mat){
	
	for(int i=mat.rows(); i>0; --i) {
		++mat.bottomRightCorner(i,i)(0,0);
	}
}

This version only works for square matrices, I guess you get the idea, 
though.


Christoph


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Dipl.-Inf. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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