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# numpy.ma.diag

`numpy.ma.``diag`(v, k=0)

  Extract a diagonal or construct a diagonal array.

  Parameters: | v : array_like If v is a 2-dimensional array, return a copy of its k-th diagonal. If v is a 1-dimensional array, return a 2-dimensional array with v on the k-th diagonal. k : int, optional Diagonal in question. The defaults is 0.

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

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