numpy.diag#

numpy.diag(v, k=0)[source]#

Extract a diagonal or construct a diagonal array.

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:

varray_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.
kint, 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:

outndarray: The extracted diagonal or constructed diagonal array.

See also

diagonal: Return specified diagonals.
diagflat: Create a 2-D array with the flattened input as a diagonal.
trace: Sum along diagonals.
triu: Upper triangle of an array.
tril: Lower triangle of an 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)
array([0, 4, 8])
>>> np.diag(x, k=1)
array([1, 5])
>>> np.diag(x, k=-1)
array([3, 7])

>>> np.diag(np.diag(x))
array([[0, 0, 0],
       [0, 4, 0],
       [0, 0, 8]])