Re: [eigen] in-place transpose

[jacob@xxxxxxxxxxxxxxx]

OK for the idea, and the name sounds good to me.

For now, in the case of a square matrix, I think we can already do  
quickly an implementation that avoids the temporary and that will  
leverage whatever optimizations we implement for triangular matrices:

m.template part<StrictlyUpper>()
 .swap(
   m.transpose().template part<StrictlyUpper>()
 );

Cheers,
Benoit

Gael Guennebaud <gael.guennebaud@xxxxxxxxx> a écrit :

> Hi all,
>
> even though the transposition in eigen is in most cases a free
> operation, sometime we really want to transpose the elements of a
> matrix. In that case we have to carefully write:
>
> m.set(m.transpose().eval());
>
> and if the matrix is square, we can also do:
>
> m = m.transpose().eval();
>
> So the first remark is that I'm pretty sure that most people will
> forget to add the .eval() leading to hard to find bugs.  Secondly this
> is quite inefficient because it generates a useless copy to a
> temporary. So what about adding a "transposeInPlace()" function ?
> Currently we can simply define it using a temporary and optimize it
> later with tricky algorithms for rectangular matrices:
> http://en.wikipedia.org/wiki/In-place_matrix_transposition.
>
> ok ? any better idea for the function name ?
>
>
> gael.
>
> ---



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