Eigenvalues function not working properly

Asked Mar 27 '18 at 01:15

Active Mar 27 '18 at 01:17

Viewed 25 times

I am trying to simply find the Eigenvalues of any matrix. I have set up M to be a 3 by 3 matrix filled with random values:

M = Table[RandomInteger[{-10, 10}], {i, 1, 3, 1}, {j, 1, 3, 1}]

This produces something like:

 {{7, 10, -3}, {1, -4, -8}, {7, -8, 5}}.

Then I ask Mathematica to find the Eigenvalues of the matrix:

Eigenvalues[M]

It returns this:

{Root[1258 - 66 #1 - 8 #1^2 + #1^3 &, 3], 
 Root[1258 - 66 #1 - 8 #1^2 + #1^3 &, 2], 
 Root[1258 - 66 #1 - 8 #1^2 + #1^3 &, 1]}

I know that is know the correct answer, but I am not sure what I am doing wrong. The only matrix I have tried for which Eigenvalues works properly is the Identity matrix

edited Mar 27 '18 at 01:17

J. M.'s missing motivation

124,525
11
401
574

asked Mar 27 '18 at 01:15

Cory Russ

I read that post you linked before posting this and it was of no help whatsoever :( – Cory Russ Mar 27 '18 at 01:22
1

Use ToRadicals[] on the result to get explicit radical expressions, as noted in this answer. More directly, try Eigenvalues[{{7, 10, -3}, {1, -4, -8}, {7, -8, 5}}, Cubics -> True]. – J. M.'s missing motivation Mar 27 '18 at 01:27
Ah, I kept expecting numbers, but now that I got it this far, I can take it from here. Thanks! – Cory Russ Mar 27 '18 at 01:33

Eigenvalues function not working properly

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