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.
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Answer
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.