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MathGroup Archive 2005

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Re: Eigensystem Bug? OS-X

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56267] Re: Eigensystem Bug? OS-X
  • From: carlos at colorado.edu
  • Date: Wed, 20 Apr 2005 05:32:23 -0400 (EDT)
  • References: <d3o0f3$bnc$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

On my old G4 laptop running MacOS, and calling
your matrix A:

Print[Timing[Eigenvalues[Rationalize[A]]//InputForm]];

{0.133333 Second, {-6, -6, -6, -6, 0, 0, 6, 6, 6,
    6, -3*Sqrt[2], -3*Sqrt[2], -3*Sqrt[2], -3*Sqrt[2], 3*Sqrt[2],
3*Sqrt[2], 3*Sqrt[2], 3*Sqrt[2]}}

Note that all eigenvalues of the rationalized matrix are real.
In floating form and using Chop to get rid of tiny scraps:

Print[Timing[Chop[Eigenvalues[A]]//InputForm]];

{0. Second, {-6.000000000000011,
    6.000000000000005, -6.0000000000000036, -6.000000000000003,
    6.000000000000001, 5.999999999999999,
    5.999999999999997, -5.999999999999993, -4.242640687119292,
-4.2426406871192865, 4.242640687119285, 4.242640687119285,
    4.242640687119284, -4.242640687119283,
    4.242640687119282, -4.242640687119281, 0, 0}}


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