def apply_R(R, A):
    """
    Apply the rotation on the set of vectors A.

    Args:
      R (numpy.matrix): a rotation matrix.
      A (numpy.matrix): the set of vectors to rotate.

    Returns:
      (numpy.matrix): the set of vectors, rotated by the matrix.
    """
    A2 = R*A.T
    A2 = A2.T
    return A2