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DOC: clarification on the `which` parameter of ARPACK. #388

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merged 1 commit into from Dec 21, 2012

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fabianp commented Dec 18, 2012

I've had a hard time understanding the which parameter of ARPACK, so
I'm submitting this patch with the hope that it becomes clearer.

Changes:

  • Eigenvectors have all norm 1, thus the parameter which is
    applied to eigenvalues and not eigenvectors.
  • Clarification on what magnitude means in the context of
    complex eigenvalues.
  • Clarification on what 'LA', 'SA' means. ARPACK docs refer to them
    as Largest/Smallest Algebraic value: those are real numbers with
    its respective sign (not in absolute value). I could not understand
    what was meant before as Largest Amplitude.
DOC: clarification on the `which` parameter of ARPACK.
I've had a hard time understanding the `which` parameter of ARPACK, so
I'm submitting this patch with the hope that it becomes clearer.

Changes:

   * Eigenvectors have all norm 1, thus the parameter `which` is
     applied to eigenvalues and not eigenvectors.

   * Clarification on what magnitude means in the context of
     complex eigenvalues.

   * Clarification on what 'LA', 'SA' means. ARPACK docs refer to them
     as Largest/Smallest Algebraic value: those are real numbers with
     its respective sign (not in absolute value). I could not understand
     what was meant before as `Largest Amplitude`.
Member

jakevdp commented Dec 18, 2012

Nice - I think that is much clearer - Thanks! I'm fine to merge this - I'll give it a couple days to see if there are other comments.

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fabianp commented Dec 18, 2012

OK glad you liked it!

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jakevdp commented Dec 21, 2012

Merging - thanks Fabian

jakevdp added a commit that referenced this pull request Dec 21, 2012

Merge pull request #388 from fabianp/arpack_doc
DOC: clarification on the `which` parameter of ARPACK.

@jakevdp jakevdp merged commit a7c0e1e into scipy:master Dec 21, 2012

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