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sfan1-Visitor
1-Visitor
November 12, 2015
Question

Interpret the result of eigenvecs

  • November 12, 2015
  • 5 replies
  • 1940 views

Hi, everyone

Here I am trying to find the eigenvectors of C using the function eigenvecs,

Capture.PNG

I know eigenvecs returns to all the eigenvectors of C,

My hand calculation shows the two eigenvectors corresponding to the two eigenvalues should be

[0.39;1] and [-0.64;1],

QCapture.PNG

So what does [1.56;1] and [-2.56;1] represent?

Thank you very much!

Shawn

5 replies

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RichardJ19-Tanzanite
19-Tanzanite
November 12, 2015

In your last expression you have a square root, which has two possible solutions (+ or -). Mathcad is showing you the two solutions.

 

Edit: Also see my comment about the use of the float keyword in this thread (near the end): incompatible units - PTC Community

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sfan1-VisitorAuthor
1-Visitor
November 12, 2015

Then for the eigenvectors, which pair should I use?

How to verify the ones that correspond to my hand calculation?

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RichardJ19-Tanzanite
19-Tanzanite
November 12, 2015

Well, that's the tricky thing about square roots. There is a common misconception that sqrt(x) has two solutions. It doesn't. It has two possible solutions. Absent any other information, you can only know that one of those solutions is the correct, one, but you can't know which. So what to do? One possibility is to find other information that resolves the dilemma. Another is to reformulate the problem to avoid the square root. In this particular case I'll make the observation that the way you solved for the eigenvectors by hand is not the same as the way you had Mathcad solve for them

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