sort eigenvalues and associated eigenvectors after using numpy.linalg.eig in python

Question

I'm using numpy.linalg.eig to obtain a list of eigenvalues and eigenvectors:

A = someMatrixArray from numpy.linalg import eig as eigenValuesAndVectors  solution = eigenValuesAndVectors(A)  eigenValues = solution[0] eigenVectors = solution[1] 

I would like to sort my eigenvalues (e.g. from lowest to highest), in a way I know what is the associated eigenvector after the sorting.

I'm not finding any way of doing that with python functions. Is there any simple way or do I have to code my sort version?

Answer 1

Use numpy.argsort. It returns the indices one would use to sort the array.

import numpy as np import numpy.linalg as linalg  A = np.random.random((3,3)) eigenValues, eigenVectors = linalg.eig(A)  idx = eigenValues.argsort()[::-1]    eigenValues = eigenValues[idx] eigenVectors = eigenVectors[:,idx] 

If the eigenvalues are complex, the sort order is lexicographic (that is, complex numbers are sorted according to their real part first, with ties broken by their imaginary part).