Predict frames of a video using 3 newly proposed and complementary methods:
1. Multi scale cnn
2. GAN
3. Image gradient difference loss


Datasets:
-----------
* UCF101
* Sports1M


GAN
------
Generator:
   * Input: several frames of video from dataset
   * output: next frame of video

Discriminator:
   * input: original and last frame
   * output: is the last frame from dataset or generated

Problem: Still blurry on edges on moving object.
Solution: Image gradient difference loss

Szegedy et al. were (to the best of my knowledge) the first to describe the phenomen of adversarial examples as researched today. Specifically, they described the main objective in order to obtain adversarial examples as

$\arg\min_r \|r\|_2$ s.t. $f(x+r)=l$ and $x+r$ being a valid image

where $f$ is the neural network and $l$ the target class (i.e. targeted adversarial example). In the paper, they originally headlined the section by “blind spots in neural networks”. While they give some explanation and provide experiments, also introducing the notion of transferability of adversarial examples and an idea of adversarial examples used as regularization during training, many questions are left open. The given conclusion, that these adversarial examples are highly unlikely and that these examples lie dense within regular training examples are controversial in the literature.

This article makes the argument for *interactive* language learning, motivated by some nice recent small-domain success. I can certainly agree with the motivation: if language is used in conversation, shouldn't we be building models which know how to behave in conversation?

The authors develop a standard multi-agent communication paradigm, where two agents learn communicate in a single-round reference game. (No references to e.g. Kirby or any [ILM][1] work, which is in the same space.) Agent `A1` examines a referent `R` and "transmits" a one-hot utterance representation to `A2`, who must successfully identify `R` given the utterance. The one-round conversations are a success when `A2` picks the correct referent `R`. The two agents are jointly trained to maximize this success metric via REINFORCE (policy gradient).

**This is mathematically equivalent to [the NVIL model (Mnih and Gregor, 2014)][2]**, an autoencoder with "hard" latent codes which is likewise trained by policy gradient methods.

They perform a nice thorough evaluation on both successful and "cheating" models. This will serve as a useful reference point / starting point for people interested in interactive language acquisition.

The way clear is forward, I think: let's develop agents in more complex environments, interacting in multi-round conversations, with more complex / longer utterances.

[1]: http://cocosci.berkeley.edu/tom/papers/IteratedLearningEvolutionLanguage.pdf
[2]: https://arxiv.org/abs/1402.0030

#### Introduction

* Introduces fastText, a simple and highly efficient approach for text classification.
* At par with deep learning models in terms of accuracy though an order of magnitude faster in performance. 
* [Link to the paper](http://arxiv.org/abs/1607.01759v3)
* [Link to code](https://github.com/facebookresearch/fastText)

#### Architecture

* Built on top of linear models with a rank constraint and a fast loss approximation.
* Start with word representations that are averaged into text representation and feed them to a linear classifier.
* Think of text representation as a hidden state that can be shared among features and classes.
* Softmax layer to obtain a probability distribution over pre-defined classes.
* High computational complexity $O(kh)$, $k$ is the number of classes and $h$ is dimension of text representation.

##### Hierarchial Softmax

* Based on Huffman Coding Tree
* Used to reduce complexity to $O(hlog(k))$
* Top T results (from the tree) can be computed efficiently $O(logT)$ using a binary heap.

##### N-gram Features

* Instead of explicitly using word order, uses a bag of n-grams to maintain efficiency without losing on accuracy.
* Uses [hashing trick](https://arxiv.org/pdf/0902.2206.pdf) to maintain fast and memory efficient mapping of the n-grams.

#### Experiments

##### Sentiment Analysis

* fastText benefits by using bigrams.
* Outperforms [char-CNN](http://arxiv.org/abs/1502.01710v5) and [char-CRNN](http://arxiv.org/abs/1602.00367v1) and performs a bit worse than [VDCNN](http://arxiv.org/abs/1606.01781v1).
* Order of magnitudes faster in terms of training time.
* Note: fastText does not use pre-trained word embeddings.

##### Tag Prediction

* fastText with bigrams outperforms [Tagspace](http://emnlp2014.org/papers/pdf/EMNLP2014194.pdf).
* fastText performs upto 600 times faster at test time.

Kurakin et al. present some larger scale experiments using adversarial training on ImageNet to increase robustness. In particular, they claim to be the first using adversarial training on ImageNet. Furthermore, they provide experiments underlining the following conclusions:
- Adversarial training can also be seen as regularizer. This, however, is not surprising as training on noisy training samples is also known to act as regularization.
- Label leaking describes the observation that an adversarially trained model is able to defend against (i.e. correctly classify) an adversarial example which has been computed by knowing to true label while not defending against adversarial examples that were crafted without knowing the true label. This means that crafting adversarial examples without guidance by the true label might be beneficial (in terms of a stronger attack).
- Model complexity seems to have an impact on robustness after adversarial training. However, from the experiments, it is hard to deduce how this connection might look exactly.

Also see this summary at [davidstutz.de](https://davidstutz.de/category/reading/).