eros((5, 3), int)
    >>> np.fill_diagonal(a, 4, wrap=True)
    >>> a
    array([[4, 0, 0],
           [0, 4, 0],
           [0, 0, 4],
           [0, 0, 0],
           [4, 0, 0]])

    >>> # wide matrices
    >>> a = np.zeros((3, 5), int)
    >>> np.fill_diagonal(a, 4, wrap=True)
    >>> a
    array([[4, 0, 0, 0, 0],
           [0, 4, 0, 0, 0],
           [0, 0, 4, 0, 0]])

    The anti-diagonal can be filled by reversing the order of elements
    using either `numpy.flipud` or `numpy.fliplr`.

    >>> a = np.zeros((3, 3), int);
    >>> np.fill_diagonal(np.fliplr(a), [1,2,3])  # Horizontal flip
    >>> a
    array([[0, 0, 1],
           [0, 2, 0],
           [3, 0, 0]])
    >>> np.fill_diagonal(np.flipud(a), [1,2,3])  # Vertical flip
    >>> a
    array([[0, 0, 3],
           [0, 2, 0],
           [1, 0, 0]])

    Note that the order in which the diagonal is filled varies depending
    on the flip function.
    r