def sg_log(tensor, opt):
    r"""Log transform a dense tensor

    See `tf.log()` in tensorflow.

    Args:
      tensor: A `Tensor` ( automatically given by chain )
      opt:
        name: If provided, replace current tensor's name.

    Returns:
        A `Tensor`.
    """
    return tf.log(tensor + tf.sg_eps, name=opt.name)