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https://issues.apache.org/jira/browse/MATH-297?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12767433#action_12767433
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Axel Kramer commented on MATH-297:
----------------------------------
If I'm expanding my testcase to the snippet below, I'm now getting an
eigenvector with all "negative values" at index 1.
I think this should be avoided.
See also the solution computed by Ted Dunning on the mailing list:
http://www.mail-archive.com/[email protected]/msg12038.html
double[][] m = { { 0.0, 1.0, -1.0 }, { 1.0, 1.0, 0.0 }, { -1.0, 0.0, 1.0 }
};
RealMatrix rm = new Array2DRowRealMatrix(m);
assertEquals(rm.toString(),
"Array2DRowRealMatrix{{0.0,1.0,-1.0},{1.0,1.0,0.0},{-1.0,0.0,1.0}}");
EigenDecompositionImpl ed = new EigenDecompositionImpl(rm,
MathUtils.SAFE_MIN);
RealVector rv0 = ed.getEigenvector(0);
RealVector rv1 = ed.getEigenvector(1);
RealVector rv2 = ed.getEigenvector(2);
assertEquals(rv0.toString(), "{0,58; 0,58; -0,58}");
assertEquals(rv1.toString(), "{-0; -0,71; -0,71}");
assertEquals(rv2.toString(), "{0,82; -0,41; 0,41}");
> Eigenvector computation incorrectly returning vectors of NaNs
> -------------------------------------------------------------
>
> Key: MATH-297
> URL: https://issues.apache.org/jira/browse/MATH-297
> Project: Commons Math
> Issue Type: Bug
> Affects Versions: 2.0
> Reporter: Phil Steitz
> Fix For: 2.1
>
>
> As reported by Axel Kramer on commons-dev, the following test case succeeds,
> but should fail:
> {code}
> public void testEigenDecomposition() {
> double[][] m = { { 0.0, 1.0, -1.0 }, { 1.0, 1.0, 0.0 }, { -1.0,0.0, 1.0 }
> };
> RealMatrix rm = new Array2DRowRealMatrix(m);
> assertEquals(rm.toString(),
> "Array2DRowRealMatrix{{0.0,1.0,-1.0},{1.0,1.0,0.0},{-1.0,0.0,1.0}}");
> EigenDecompositionImpl ed = new EigenDecompositionImpl(rm,
> MathUtils.SAFE_MIN);
> RealVector rv0 = ed.getEigenvector(0);
> assertEquals(rv0.toString(), "{(NaN); (NaN); (NaN)}");
> }
> {code}
> ed.getRealEigenvalues() returns the correct eigenvalues (2, 1, -1), but all
> three eigenvectors contain only NaNs.
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