[Scipy-tickets] [SciPy] #889: arpack.eigen gives wrong answer when k = 1

SciPy Trac scipy-tickets@scipy....
Tue Apr 20 19:01:41 CDT 2010

#889: arpack.eigen gives wrong answer when k = 1
 Reporter:  kyleabeauchamp       |       Owner:  wnbell
     Type:  defect               |      Status:  new   
 Priority:  normal               |   Milestone:  0.8.0 
Component:  scipy.sparse.linalg  |     Version:  0.7.0 
 Keywords:                       |  

Comment(by ysr):

 Please check the eigenvalues for k=1, k=2. If the two eigenvalues are the
 same (i.e., repeated), then note that the eigenvectors for repeated
 eigenvalues can be anything in the linear subspace spanned by the two
 eigenvectors. For example, if a matrix has two zero eigenvalues with
 eigenvectors (unnormalized) [2,2,2,-3,-3] and [2,2,2,3,3], they can also
 be reported as [0,0,0,0,0] and [0,0,0,1,1].

 This stuff only happens for repeated eigenvalues.

Ticket URL: <http://projects.scipy.org/scipy/ticket/889#comment:3>
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