def shear(angle):
    """ Construct a homogeneous 2D shear matrix.
    Args
        angle: the shear angle in radians
    Returns
        the shear matrix as 3 by 3 numpy array
    """
    return np.array([
        [1, -np.sin(angle), 0],
        [0,  np.cos(angle), 0],
        [0, 0, 1]
    ])
 Construct a homogeneous 2D shear matrix.
    Args
        angle: the shear angle in radians
    Returns
        the shear matrix as 3 by 3 numpy array
    
keras_retinanet/utils/transform.py