`numpy:diag`

source: /numpy/lib/_twodim_base_impl.py:258

Signature

def diag(v, k = 0)

Summary

Extract a diagonal or construct a diagonal array.

Extended Summary

See the more detailed documentation for numpy.diagonal if you use this function to extract a diagonal and wish to write to the resulting array; whether it returns a copy or a view depends on what version of numpy you are using.

Parameters

v : array_like: If v is a 2-D array, return a copy of its k-th diagonal. If v is a 1-D array, return a 2-D array with v on the k-th diagonal.
k : int, optional: Diagonal in question. The default is 0. Use k>0 for diagonals above the main diagonal, and k<0 for diagonals below the main diagonal.

Returns

out : ndarray: The extracted diagonal or constructed diagonal array.

Examples

import numpy as np
x = np.arange(9).reshape((3,3))
x

✓

array([[0, 1, 2],
       [3, 4, 5],
       [6, 7, 8]])

np.diag(x)
np.diag(x, k=1)
np.diag(x, k=-1)

✓

array([3, 7])

np.diag(np.diag(x))

✓

array([[0, 0, 0],
       [0, 4, 0],
       [0, 0, 8]])

Aliases

numpy.diag