numpy.diag — NumPy v1.13 Manual (original) (raw)
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: | 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. |
See also
Return specified diagonals.
Create a 2-D array with the flattened input as a diagonal.
Sum along diagonals.
Upper triangle of an array.
Lower triangle of an array.
Examples
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]])