[ITK-users] Symmetric eigen analysis discrepancy

[Olivier Commowick]

Hello all,

I have been experiencing a problem when using the itk SymmetricEigenAnalysis class in ITK. When using this class, it sometimes produces NaN eigenvalues/vectors. On the contrary, the vnl_symmetric_eigensystem doesn’t seem to have a problem (and neither does matlab). Looking at the documentation, it seems both use QL decomposition but not implemented in the same place. In addition, the vnl one is said to be not thread safe, although it’s the one working for me.

In fact, I have isolated one 3x3 matrix for which I always have the problem. 

A = 
[7.503107128706855667859804009212206062302e-53 1.870107888834986371214720644344813262375e-52 -8.662047753682068190087788895125120421821e-27;
1.870107888834986371214720644344813262375e-52 4.661140319458029838073740773908360767728e-52 -2.15896741973055935210319454393408888029e-26;
-8.662047753682068190087788895125120421821e-27 -2.15896741973055935210319454393408888029e-26 1]

It’s a weird one I know, but again vnl (and matlab) works great on it. Would there be anyone who knows the QL decomposition code enough to help me understand and possibly correct the ITK class so that it does the same as the VNL one ?

Thanks a lot in advance.

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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
Email: Olivier.Commowick at inria.fr
Web: http://olivier.commowick.org/