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Bases of Generalized Eigenvectors

  1. Apr 25, 2007 #1
    Hi all.

    So I'm a bit confused about finding a basis of generalized eigenvectors for an operator that is not diagonalizable. I have some "steps" in mind, but maybe someone can help me out here:

    1) Find the eigenvalues of the matrix/operator
    2) Find the eigenspaces corresponding to each eigenvector; for those which do not have a "big enough" basis, we must compute the generalized eigenspace for that eigenvalue
    3) Here's where I'm confused! I know that the generalized eigenspace is given by kernel((T-λI)^p) for some positive integer p, and that (T-λI)^(p-1) is an eigenvector of T. I guess I'm lost with calculating this nullspace.

    Are we literally taking the matrix (T-λI) and raising it to the power p? Because it doesn't seem to work on any problems I've attempted so far... anyone know? :eek:
  2. jcsd
  3. Apr 26, 2007 #2
    Could you show us first a small example of an operator that is not diagonalizable.
    Take then the opportunity to illustrate the steps 1 and 2.
    Then we can discuss maybe step 3.
  4. Apr 26, 2007 #3


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    I recommend you do what lalbatross suggests- looking at a specific simple example might help you see what is happening.

    You first find the lowest integer p such that (T-λI)^p has the entire eigenspace of [itex]\lamba[/itex] as kernel. But I don't understand what you mean by "(T-λI)^(p-1) is an eigenvector of T". (T-λI)^(p-1) isn't a vector, it is a linear transformation. Did you mean to apply it to something?
  5. May 5, 2008 #4
    I wonder if there is any online document available to show us how to compute all the generalized eigenvectors?
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