Pairwise cosine distance between two matrices.
    :param A: a matrix.
    :param B: a matrix.

    :returns: A tensor for the pairwise cosine between A and B.

def pairwise_cos_distance(A, B):
    """Pairwise cosine distance between two matrices.
    :param A: a matrix.
    :param B: a matrix.

    :returns: A tensor for the pairwise cosine between A and B.
    """
    normalized_A = tf.nn.l2_normalize(A, dim=1)
    normalized_B = tf.nn.l2_normalize(B, dim=1)
    prod = tf.matmul(normalized_A, normalized_B, adjoint_b=True)
    return 1 - prod