How do you get the magnitude of a vector at Numpy?

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In keeping with the "There's only one obvious way to do it", how do you get the magnitude of a vector (1D array) in Numpy?

def mag(x):
    return math.sqrt(sum(i**2 for i in x))

The above works, but I cannot believe that I must specify such a trivial and core function myself.


The function you're after is numpy.linalg.norm. (I reckon it should be in base numpy as a property of an array -- say x.norm() -- but oh well).

import numpy as np
x = np.array([1,2,3,4,5])
np.linalg.norm(x)

You can also feed in an optional ord for the nth order norm you want. Say you wanted the 1-norm:

np.linalg.norm(x,ord=1)

And so on.