Re: [eigen] Unexpected behavior with rowwise().reverse()

[Christoph Hertzberg <chtz@xxxxxxxxxxxxxxxxxxxxxxxx>]

On 22.11.2013 17:52, Rob Conde wrote:
> Results:
> 1 2 3 4 5
> 5 4 3 4 5
> 5 4 3 2 1
>
> Isn't eigen supposed to detect these scenarios and call eval if necessary?

It is very hard to detect all possible aliasing issues. If we introduced 
a detection for this case, we would rather assert than calling eval -- 
at least we already do so for A = A.transpose();

There is a blah.reverseInPlace(); however this seems to be missing for 
rowwise() and colwise().
As a workaround until we implement that, something like this should work:
  int width = blah.cols()/2;
  blah.leftCols(3).swap(blah.rightCols(3).rowwise().reverse());

Christoph

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Dipl.-Inf., Dipl.-Math. Christoph Hertzberg
Cartesium 0.049
Universität Bremen
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28359 Bremen

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