ALBEF introduces a contrastive loss to align the image and text representations before fusing them through cross-modal attention. This enables more grounded vision and language representation learning. ALBEF also doesn't require bounding box annotations. The model consists of an image encode, a text encoder, and a multimodal encoder. The image-text contrastive loss helps to align the unimodal representations of an image-text pair before fusion. The image-text matching loss and a masked language modeling loss are applied to learn multimodal interactions between image and text. In addition, momentum distillation is used to generate pseudo-targets. This improves learning with noisy data.

ALBEF

Align before Fuse: Vision and Language Representation Learning with Momentum Distillation

Original paper : Integrating Constraints and Metric Learning in Semi-Supervised Clustering, Bilenko et al. 2004

MPCK-Means

**Go-Explore** is a family of algorithms aiming to tackle two challenges with effective exploration in reinforcement learning: algorithms forgetting how to reach previously visited states ("detachment") and from failing to first return to a state before exploring from it ("derailment").

To avoid detachment, Go-Explore builds an archive of the different states it has visited in the environment, thus ensuring that states cannot be forgotten. Starting with an archive beginning with the initial state, the archive is built iteratively. In Go-Explore we:

(a) Probabilistically select a state from the archive, preferring states associated with promising cells. 

(b) Return to the selected state, such as by restoring simulator state or by running a goal-conditioned policy. 

(c) Explore from that state by taking random actions or sampling from a trained policy. 

(d) Map every state encountered during returning and exploring to a low-dimensional cell representation. 

(e) Add states that map to new cells to the archive and update other archive entries.

Go-Explore

Go-Explore: a New Approach for Hard-Exploration Problems

**Vision-and-Language BERT** (**ViLBERT**) is a [BERT](https://paperswithcode.com/method/bert)-based model for learning task-agnostic joint representations of image content and natural language. ViLBERT extend the popular BERT architecture to a multi-modal two-stream model, processing both visual and textual inputs in separate streams that interact through co-attentional [transformer](https://paperswithcode.com/method/transformer) layers.

ViLBERT

ViLBERT: Pretraining Task-Agnostic Visiolinguistic Representations for Vision-and-Language Tasks

**BoundaryNet** is a resizing-free approach for layout annotation. The variable-sized user selected region of interest is first processed by an attention-guided skip network. The network optimization is guided via Fast Marching distance maps to obtain a good quality initial boundary estimate and an associated feature representation. These outputs are processed by a Residual Graph [Convolution](https://paperswithcode.com/method/convolution) Network optimized using Hausdorff loss to obtain the final region boundary.

BoundaryNet

BoundaryNet: An Attentive Deep Network with Fast Marching Distance Maps for Semi-automatic Layout Annotation

A **Gated Linear Network**, or **GLN**, is a type of backpropagation-free neural architecture. What distinguishes GLNs from contemporary neural networks is the distributed and local nature of their credit assignment mechanism; each neuron directly predicts the target, forgoing the ability to learn feature representations in favor of rapid online learning. Individual neurons can model nonlinear functions via the use of data-dependent gating in conjunction with online convex optimization. 

GLNs are feedforward networks composed of many layers of gated geometric mixing neurons as shown in the Figure . Each neuron in a given layer outputs a gated geometric mixture of the predictions from the previous layer, with the final layer consisting of just a single neuron. In a supervised learning setting, a $\mathrm{GLN}$ is trained on (side information, base predictions, label) triplets $\left(z\_{t}, p\_{t}, x\_{t}\right)_{t=1,2,3, \ldots}$ derived from input-label pairs $\left(z\_{t}, x\_{t}\right)$. There are two types of input to neurons in the network: the first is the side information $z\_{t}$, which can be thought of as the input features; the second is the input to the neuron, which will be the predictions output by the previous layer, or in the case of layer 0 , some (optionally) provided base predictions $p\_{t}$ that typically will be a function of $z\_{t} .$ Each neuron will also take in a constant bias prediction, which helps empirically and is essential for universality guarantees.

Weights are learnt in a Gated Linear Network using Online Gradient Descent (OGD) locally at each neuron. They key observation is that as each neuron $(i, k)$ in layers $i>0$ is itself a gated geometric mixture, all of these neurons can be thought of as individually predicting the target. Given side information $z$ , each neuron $(i, k)$ suffers a loss convex in its active weights $u:=w\_{i k c\_{i k}(z)}$ of
$$
\ell\_{t}(u):=-\log \left(\operatorname{GEO}\_{u}\left(x_{t} ; p\_{i-1}\right)\right)
$$

Gated Linear Networks

**WordPiece** is a subword segmentation algorithm used in natural language processing.  The vocabulary is initialized with individual characters in the language, then the most frequent combinations of symbols in the vocabulary are iteratively added to the vocabulary. The process is:

1. Initialize the word unit inventory with all the characters in the text.
2. Build a language model on the training data using the inventory from 1.
3. Generate a new word unit by combining two units out of the current word inventory to increment the word unit inventory by one. Choose the new word unit out of all the possible ones that increases the likelihood on the training data the most when added to the model.
4. Goto 2 until a predefined limit of word units is reached or the likelihood increase falls below a certain threshold.

Text: [Source](https://stackoverflow.com/questions/55382596/how-is-wordpiece-tokenization-helpful-to-effectively-deal-with-rare-words-proble/55416944#55416944)

Image: WordPiece as used in [BERT](https://paperswithcode.com/method/bert)

WordPiece

Google's Neural Machine Translation System: Bridging the Gap between Human and Machine Translation

**Gradient Sparsification** is a technique for distributed training that sparsifies stochastic gradients to reduce the communication cost, with minor increase in the number of iterations. The key idea behind our sparsification technique is to drop some coordinates of the stochastic gradient and appropriately amplify the remaining coordinates to ensure the unbiasedness of the sparsified stochastic gradient. The sparsification approach can significantly reduce the coding length of the stochastic gradient and only slightly increase the variance of the stochastic gradient.

Gradient Sparsification

Gradient Sparsification for Communication-Efficient Distributed Optimization

**PanGu-$α$** is an autoregressive language model (ALM) with up to 200 billion parameters pretrained on a large corpus of text, mostly in Chinese language. The architecture of PanGu-$α$ is based on Transformer, which has been extensively used as the backbone of a variety of pretrained language models such as [BERT](https://paperswithcode.com/method/bert) and [GPT](https://paperswithcode.com/method/gpt). Different from them, there's an additional query layer developed on top of Transformer layers which aims to explicitly induce the expected output.

PanGu-$α$

PanGu-$α$: Large-scale Autoregressive Pretrained Chinese Language Models with Auto-parallel Computation

**Low-Rank Factorization-based Multi-head Attention Mechanism**, or **LAMA**, is a type of attention module that uses low-rank factorization to reduce computational complexity. It uses low-rank bilinear pooling to construct a structured sentence representation that attends to multiple aspects of a sentence.

LAMA

Low Rank Factorization for Compact Multi-Head Self-Attention

**CBHG** is a building block used in the [Tacotron](https://paperswithcode.com/method/tacotron) text-to-speech model. It consists of a bank of 1-D convolutional filters, followed by highway networks and a bidirectional gated recurrent unit ([BiGRU](https://paperswithcode.com/method/bigru)). 

The module is used to extract representations from sequences. The input sequence is first
convolved with $K$ sets of 1-D convolutional filters, where the $k$-th set contains $C\_{k}$ filters of width $k$ (i.e. $k = 1, 2, \dots , K$). These filters explicitly model local and contextual information (akin to modeling unigrams, bigrams, up to K-grams). The [convolution](https://paperswithcode.com/method/convolution) outputs are stacked together and further max pooled along time to increase local invariances. A stride of 1 is used to  preserve the original time resolution. The processed sequence is further passed to a few fixed-width 1-D convolutions, whose outputs are added with the original input sequence via residual connections. [Batch normalization](https://paperswithcode.com/method/batch-normalization) is used for all convolutional layers. The convolution outputs are fed into a multi-layer [highway network](https://paperswithcode.com/method/highway-network) to extract high-level features. Finally, a bidirectional [GRU](https://paperswithcode.com/method/gru) RNN is stacked on top to extract sequential features from both forward and backward context.

CBHG

Tacotron: Towards End-to-End Speech Synthesis

**GAN-TTS** is a generative adversarial network for text-to-speech synthesis. The architecture is composed of a conditional feed-forward generator producing raw speech audio, and an ensemble of discriminators which operate on random windows of different sizes. The discriminators analyze the audio both in terms of general realism, as well as how well the audio corresponds to the utterance that should be pronounced.

The generator architecture consists of several GBlocks, which are residual based (dilated) [convolution](https://paperswithcode.com/method/convolution) blocks. GBlocks 3–7 gradually upsample the temporal dimension of hidden representations by factors of 2, 2, 2, 3, 5, while the number of channels is reduced by GBlocks 3, 6 and 7 (by a factor of 2 each). The final convolutional layer with [Tanh activation](https://paperswithcode.com/method/tanh-activation) produces a single-channel audio waveform.

Instead of a single discriminator, GAN-TTS uses an ensemble of Random Window Discriminators (RWDs) which operate on randomly sub-sampled fragments of the real or generated samples. The ensemble allows for the evaluation of audio in different complementary ways.

GAN-TTS

High Fidelity Speech Synthesis with Adversarial Networks

The NA method can be divided into two steps: (i) Training a neural network approximation of f , and (ii) inference of xˆ. Step (i) is conventional and involves training a generic neural network on a dataset
ˆ
of input/output pairs from the simulator, denoted D, resulting in f, an approximation of the forward ˆ
model. This is illustrated in the left inset of Fig 1. In step (ii), our goal is to use ∂f/∂x to help us gradually adjust x so that we achieve a desired output of the forward model, y. This is similar to many classical inverse modeling approaches, such as the popular Adjoint method [8, 9]. For many practical
ˆ
expression for the simulator, from which it is trivial to compute ∂f/∂x, and furthermore, we can use modern deep learning software packages to efficiently estimate gradients, given a loss function L.
More formally, let y be our target output, and let xˆi be our current estimate of the solution, where i indexes each solution we obtain in an iterative gradient-based estimation procedure. Then we compute xˆi+1 with
inverse problems, however, obtaining ∂f/∂x requires significant expertise and/or effort, making these approaches challenging. Crucially, fˆ from step (i) provides us with a closed-form differentiable

Neural adjoint

Benchmarking deep inverse models over time, and the neural-adjoint method

**BiDet** is a binarized neural network learning method for efficient object detection. Conventional network binarization methods directly quantize the weights and activations in one-stage or two-stage detectors with constrained representational capacity, so that the information redundancy in the networks causes numerous false positives and degrades the performance significantly. On the contrary, BiDet fully utilizes the representational capacity of the binary neural networks for object detection by redundancy removal, through which the detection precision is enhanced with alleviated false positives. Specifically, the information bottleneck (IB) principle is generalized to object detection, where the amount of information in the high-level feature maps is constrained and the mutual information between the feature maps and object detection is maximized.

BiDet

BiDet: An Efficient Binarized Object Detector

**Relative Position Encodings** are a type of position embeddings for [Transformer-based models](https://paperswithcode.com/methods/category/transformers) that attempts to exploit pairwise, relative positional information. Relative positional information is supplied to the model on two levels: values and keys. This becomes apparent in the two modified self-attention equations shown below. First, relative positional information is supplied to the model as an additional component to the keys

$$ e\_{ij} = \frac{x\_{i}W^{Q}\left(x\_{j}W^{K} + a^{K}\_{ij}\right)^{T}}{\sqrt{d\_{z}}} $$

Here $a$ is an edge representation for the inputs $x\_{i}$ and $x\_{j}$. The [softmax](https://paperswithcode.com/method/softmax) operation remains unchanged from vanilla self-attention. Then relative positional information is supplied again as a sub-component of the values matrix:

$$ z\_{i} = \sum^{n}\_{j=1}\alpha\_{ij}\left(x\_{j}W^{V} + a\_{ij}^{V}\right)$$

In other words, instead of simply combining semantic embeddings with absolute positional ones, relative positional information is added to keys and values on the fly during attention calculation.

Source: [Jake Tae](https://jaketae.github.io/study/relative-positional-encoding/)

Image Source: [Relative Positional Encoding for Transformers with Linear Complexity](https://www.youtube.com/watch?v=qajudaEHuq8

Relative Position Encodings

Self-Attention with Relative Position Representations

**CodeBERT** is a bimodal pre-trained model for programming language (PL) and natural language (NL). CodeBERT learns general-purpose representations that support downstream NL-PL applications such as natural language code search, code documentation generation, etc. CodeBERT is developed with a [Transformer](https://paperswithcode.com/method/transformer)-based neural architecture, and is trained with a hybrid objective function that incorporates the pre-training task of replaced token detection, which is to detect plausible alternatives sampled from generators. This enables the utilization of both bimodal data of NL-PL pairs and unimodal data, where the former provides input tokens for model training while the latter helps to learn better generators.

CodeBERT

CodeBERT: A Pre-Trained Model for Programming and Natural Languages

**Peer-attention** is a network component which dynamically learns the attention weights using another block or input modality. This is unlike AssembleNet which partially relies on exponential mutations to explore connections. Once the attention weights are found, we can either prune the connections by only leaving the argmax over $h$ or leave them with [softmax](https://paperswithcode.com/method/softmax).

Peer-attention

AssembleNet++: Assembling Modality Representations via Attention Connections

**Strided Attention** is a factorized attention pattern that has one head attend to the previous
$l$ locations, and the other head attend to every $l$th location, where $l$ is the stride and chosen to be close to $\sqrt{n}$. It was proposed as part of the [Sparse Transformer](https://paperswithcode.com/method/sparse-transformer) architecture.

A self-attention layer maps a matrix of input embeddings $X$ to an output matrix and is parameterized by a connectivity pattern $S = \text{set}\left(S\_{1}, \dots, S\_{n}\right)$, where $S\_{i}$ denotes the set of indices of the input vectors to which the $i$th output vector attends. The output vector is a weighted sum of transformations of the input vectors:

$$ \text{Attend}\left(X, S\right) = \left(a\left(\mathbf{x}\_{i}, S\_{i}\right)\right)\_{i\in\text{set}\left(1,\dots,n\right)}$$

$$ a\left(\mathbf{x}\_{i}, S\_{i}\right) = \text{softmax}\left(\frac{\left(W\_{q}\mathbf{x}\_{i}\right)K^{T}\_{S\_{i}}}{\sqrt{d}}\right)V\_{S\_{i}} $$

$$ K\_{Si} = \left(W\_{k}\mathbf{x}\_{j}\right)\_{j\in{S\_{i}}} $$

$$ V\_{Si} = \left(W\_{v}\mathbf{x}\_{j}\right)\_{j\in{S\_{i}}} $$

Here $W\_{q}$, $W\_{k}$, and $W\_{v}$ represent the weight matrices which transform a given $x\_{i}$ into a query, key, or value, and $d$ is the inner dimension of the queries and keys. The output at each position is a sum of the values weighted by the scaled dot-product similarity of the keys and queries.

Full self-attention for autoregressive models defines $S\_{i} = \text{set}\left(j : j \leq i\right)$, allowing every element to attend to all previous positions and its own position.

Factorized self-attention instead has $p$ separate attention heads, where the $m$th head defines a subset of the indices $A\_{i}^{(m)} ⊂ \text{set}\left(j : j \leq i\right)$ and lets $S\_{i} = A\_{i}^{(m)}$. The goal with the Sparse [Transformer](https://paperswithcode.com/method/transformer) was to find efficient choices for the subset $A$.

Formally for Strided Attention, $A^{(1)}\_{i} = ${$t, t + 1, ..., i$} for $t = \max\left(0, i − l\right)$, and $A^{(2)}\_{i} = ${$j : (i − j) \mod l = 0$}. The $i$-th output vector of the attention head attends to all input vectors either from $A^{(1)}\_{i}$ or $A^{(2)}\_{i}$. This pattern can be visualized in the figure to the right.

This formulation is convenient if the data naturally has a structure that aligns with the stride, like images or some types of music. For data without a periodic structure, like text, however, the authors find that the network can fail to properly route information with the strided pattern, as spatial coordinates for an element do not necessarily correlate with the positions where the element may be most relevant in the future.

Viet-Anh on Software

AI Glossary

Tech Terminology

ALBEF

Metric Pairwise Constrained KMeans