def add_activation_summary(x, types=None, name=None, collections=None):
    """
    Call :func:`add_tensor_summary` under a reused 'activation-summary' name scope.
    This function is a no-op if not calling from main training tower.

    Args:
        x (tf.Tensor): the tensor to summary.
        types (list[str]): summary types, defaults to ``['sparsity', 'rms', 'histogram']``.
        name (str): if is None, use x.name.
        collections (list[str]): collections of the summary ops.
    """
    ndim = x.get_shape().ndims
    if ndim < 2:
        logger.warn("Cannot summarize scalar activation {}".format(x.name))
        return
    if types is None:
        types = ['sparsity', 'rms', 'histogram']
    with cached_name_scope('activation-summary'):
        add_tensor_summary(x, types, name=name, collections=collections)