NumPy ValueError The truth value of an array with more than one element is ambiguous Use a any or a all

Question

I was calculating eigenvectors and eigenvalues of a matrix in NumPy and just wanted to check the results via assert    This would throw a ValueError that I don t quite understand  since printing those comparisons works just fine  Any tips how I could get this assert   working   import numpy as np A   np array   3 5 0    5 7 12    0 12 5    eig val  eig vec   np linalg eig A  print  eigenvalue    eig val  print  eigenvector    eig vec   for col in range A shape 0        assert   A dot eig vec   col        eig val col    eig vec   col

User · Accepted Answer

As it says  it is ambiguous  Your array comparison returns a boolean array  Methods any   and all   reduce values over the array  either logical or or logical and   Moreover  you probably don t want to check for equality  You should replace your condition with   np allclose A dot eig vec   col    eig val col    eig vec   col

User · Answer

The error message explains it pretty well   ValueError  The truth value of an array with more than one element is ambiguous   Use a any   or a all     What should bool np array  False  False  True    return   You can make several plausible arguments    1  True  because bool np array x   should return the same as bool list x    and non-empty lists are truelike    2  True  because at least one element is True    3  False  because not all elements are True   and that s not even considering the complexity of the N-d case   So  since  the truth value of an array with more than one element is ambiguous   you should use  any   or  all    for example    gt  gt  gt  v   np array  1 2 3      np array  1 2 4    gt  gt  gt  v array   True   True  False   dtype bool   gt  gt  gt  v any   True  gt  gt  gt  v all   False   and you might want to consider np allclose if you re comparing arrays of floats    gt  gt  gt  np allclose np array  1 2 3 1e-8    np array  1 2 3    True

User · Answer

try this     numpy array yourvariable    followed by the command to compare  whatever you wish to

[numpy] NumPy ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

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