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pythonnumpylinear-algebraeigenvalue
user3731622
user3731622

Reputation: 5095

How does numpy.linalg.eig decide on order in which eigenvalues are returned?

When I use numpy.linalg.eig like

eValues, eVectors = numpy.linalg.eig(someMatrix)

the eValues returned are almost in descending order.

How does numpy.linalg.eig decide on order in which eigenvalues are returned?

Upvotes: 4

Views: 1398

Answers (1)

wim
wim

Reputation: 363183

Numpy makes no guarantees about that -

from the docstring:

Returns
-------
w : (..., M) array
    The eigenvalues, each repeated according to its multiplicity.
    The eigenvalues are not necessarily ordered. The resulting
    array will be always be of complex type. When `a` is real
    the resulting eigenvalues will be real (0 imaginary part) or
    occur in conjugate pairs

Numpy delegates to LAPACK for this computation, so if there is any consistent ordering you should consider it implementation detail and not rely on it.

Upvotes: 3

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