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slightly more stable eigen vector computation

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This commit is contained in:
Gael Guennebaud 2011-02-03 10:31:45 +01:00
parent a617d7f2ad
commit 5beb2f4f0d
1 changed files with 25 additions and 10 deletions
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35
bench/eig33.cpp
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@ -139,19 +139,34 @@ void eigen33(const Matrix& mat, Matrix& evecs, Vector& evals)
// }
// evecs.col(2) = evecs.col(0).cross(evecs.col(1)).normalized();
// naive version
// // naive version
// Matrix tmp;
// tmp = scaledMat;
// tmp.diagonal().array() -= evals(0);
// evecs.col(0) = tmp.row(0).cross(tmp.row(1)).normalized();
//
// tmp = scaledMat;
// tmp.diagonal().array() -= evals(1);
// evecs.col(1) = tmp.row(0).cross(tmp.row(1)).normalized();
//
// tmp = scaledMat;
// tmp.diagonal().array() -= evals(2);
// evecs.col(2) = tmp.row(0).cross(tmp.row(1)).normalized();
// a slighlty more stable version:
Matrix tmp;
tmp = scaledMat;
tmp.diagonal().array() -= evals(0);
evecs.col(0) = tmp.row(0).cross(tmp.row(1)).normalized();
tmp.diagonal ().array () -= evals (2);
evecs.col (2) = tmp.row (0).cross (tmp.row (1)).normalized ();
tmp = scaledMat;
tmp.diagonal().array() -= evals(1);
evecs.col(1) = tmp.row(0).cross(tmp.row(1)).normalized();
tmp = scaledMat;
tmp.diagonal().array() -= evals(2);
evecs.col(2) = tmp.row(0).cross(tmp.row(1)).normalized();
tmp.diagonal ().array () -= evals (1);
evecs.col(1) = tmp.row (0).cross(tmp.row (1));
Scalar n1 = evecs.col(1).norm();
if(n1<=Eigen::NumTraits<Scalar>::epsilon())
evecs.col(1) = evecs.col(2).unitOrthogonal();
else
evecs.col(1) /= n1;
evecs.col(0) = evecs.col(2).cross(evecs.col(1));
// Rescale back to the original size.
evals *= scale;