**Dropout** is a regularization technique for neural networks that drops a unit (along with connections) at training time with a specified probability $p$ (a common value is $p=0.5$). At test time, all units are present, but with weights scaled by $p$ (i.e. $w$ becomes $pw$).

The idea is to prevent co-adaptation, where the neural network becomes too reliant on particular connections, as this could be symptomatic of overfitting. Intuitively, dropout can be thought of as creating an implicit ensemble of neural networks.

A **Wide Residual Block** is a type of [residual block](https://paperswithcode.com/method/residual-block) that utilises two conv 3x3 layers (with [dropout](https://paperswithcode.com/method/dropout)). This is wider than other variants of residual blocks (for instance [bottleneck residual blocks](https://paperswithcode.com/method/bottleneck-residual-block)). It was proposed as part of the [WideResNet](https://paperswithcode.com/method/wideresnet) CNN architecture.

Wide Residual Block

Wide Residual Networks

Dropout

Dropout: A Simple Way to Prevent Neural Networks from Overfitting

**TayPO**, or **Taylor Expansion Policy Optimization**, refers to a set of algorithms that apply the $k$-th order Taylor expansions for policy optimization. This generalizes prior work, including [TRPO](https://paperswithcode.com/method/trpo) as a special case. It can be thought of unifying ideas from trust-region policy optimization and off-policy corrections. Taylor expansions share high-level similarities with both trust region policy search and off-policy corrections. To get high-level intuitions of such similarities, consider a simple 1D example of Taylor expansions. Given a sufficiently smooth real-valued function on the real line $f : \mathbb{R} \rightarrow \mathbb{R}$, the $k$-th order Taylor expansion of $f\left(x\right)$ at $x\_{0}$ is 

$$f\_{k}\left(x\right) = f\left(x\_{0}\right)+\sum^{k}\_{i=1}\left[f^{(i)}\left(x\_{0}\right)/i!\right]\left(x−x\_{0}\right)^{i}$$

where $f^{(i)}\left(x\_{0}\right)$ are the $i$-th order derivatives at $x\_{0}$. First, a common feature shared by Taylor expansions and trust-region policy search is the inherent notion of a trust region constraint. Indeed, in order for convergence to take place, a trust-region constraint is required $|x − x\_{0}| < R\left(f, x\_{0}\right)^{1}$. Second, when using the truncation as an approximation to the original function $f\_{K}\left(x\right) \approx f\left(x\right)$, Taylor expansions satisfy the requirement of off-policy evaluations: evaluate target policy with behavior data. Indeed, to evaluate the truncation $f\_{K}\left(x\right)$ at any $x$ (target policy), we only require the behavior policy "data" at $x\_{0}$ (i.e., derivatives $f^{(i)}\left(x\_{0}\right)$).

Source	Dropout: A Simple Way to Prevent Neural Networks from Overfitting
Year	2000
Data Source	CC BY-SA - https://paperswithcode.com