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12/03/12 09:26am

Good afternoon,

I upgraded to Mathematica 9. For some reasons, I have to threat with "modified Jordan form" of a matrix which is like usual Jordan form with a difference that Jordan block for eigenvalue c has c's also on the first upper superdiagonal instead of 1's, for example
c c 0
0 c c
0 0 c
instead of
c 1 0
0 c 1
0 0 c
Then I asked Mathematica 9 what is the similarity matrix between those two forms, using the function

JordanDecomposition[{{c, c, 0}, {0, c, c}, {0, 0, c}}]

The answer with my Mathematica 9 was that the similarity matrix is the identity. Mathematica 8 answered this question correctly.

Also, if I put d's instead of c's on the first upper superdiagonal, i.e.
c d 0
0 c d
0 0 c,
the answer with Mathematica 9 is correct. Or if I set c=2 for example, the similarity matrix that Mathematica 9 gives as a result is the correct one.

The constant c was cleared before running the formula (Clear[c], ClearAll[c]), so this is not a problem.

Any ideas?
Thanks and best regards,

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