[ITK-users] Problem with ITK eigensystem

[Dženan Zukić]

Hi Olivier,

I tried running you example. One thing struck me right away: ITK version is
much slower (after a few minutes running in release mod I killed it) than
VNL version (about a second in debug mode) for your input.

I can't comment the patch content or the numeric stability. Perhaps Brad
and Hans can pitch in?

Regards,
Dženan

On Tue, Jan 31, 2017 at 11:24 AM, Olivier Commowick <
Olivier.Commowick at inria.fr> wrote:

> Hello,
>
> I think I have found a bug in the behaviour of ITK’s symmetric
> eigensystem. In the attached link (http://olivier.commowick.org/
> tmp/Test.zip) you will find an example code and matrix that fails with it
> and not with VNL’s symmetric eigensystem (run on macOS 10.12, Xcode 8.2.1).
>
> It seems to me that there are subtle differences in between ITK and VNL
> versions, VNL being more robust (and the same as what Matlab gives, I
> didn’t test python). Here is what I have found so far :
>
> - the hypothenuse function (hypot for ITK and pythag for VNL) do not get
> always the exact same result up to a very far away decimal
> - some loop indices were wrong I think in the ITK eigensystem. Some do
> vary in the VNL version, not in ITK’s equivalent
>
> In the patch file attached, I have made a set of corrections that make
> things in ITK eigensystem closer to VNL but still the ITK version fails. I
> have to say I am getting completely lost here so I am calling upon the
> community for help. If anyone knows this enough, could you try the test
> attached and see if you have any ideas of what is going on. That would help
> us a lot.
>
> The test attached can be compiled with cmake and run with the text file
> included : ./test_eigensystem data.txt
>
> Thanks in advance
> Olivier
>
>
>
> ---
>
> Olivier Commowick, Ph.D.
> Research Scientist
> INRIA Rennes - Bretagne Atlantique, VISAGES Team
> Campus de Beaulieu
> 35042 Rennes
> FRANCE
>
> Phone: +33 2 99 84 25 92 <+33%202%2099%2084%2025%2092>
> Email: Olivier.Commowick at inria.fr
> Web: http://olivier.commowick.org/
>
>
>
>
>
>
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