Activation Functions

# Gaussian Error Linear Units

Introduced by Hendrycks et al. in Gaussian Error Linear Units (GELUs)

The Gaussian Error Linear Unit, or GELU, is an activation function. The GELU activation function is $x\Phi(x)$, where $\Phi(x)$ the standard Gaussian cumulative distribution function. The GELU nonlinearity weights inputs by their percentile, rather than gates inputs by their sign as in ReLUs ($x\mathbf{1}_{x>0}$). Consequently the GELU can be thought of as a smoother ReLU.

$$\text{GELU}\left(x\right) = x{P}\left(X\leq{x}\right) = x\Phi\left(x\right) = x \cdot \frac{1}{2}\left[1 + \text{erf}(x/\sqrt{2})\right],$$ if $X\sim \mathcal{N}(0,1)$.

One can approximate the GELU with $0.5x\left(1+\tanh\left[\sqrt{2/\pi}\left(x + 0.044715x^{3}\right)\right]\right)$ or $x\sigma\left(1.702x\right),$ but PyTorch's exact implementation is sufficiently fast such that these approximations may be unnecessary. (See also the SiLU $x\sigma(x)$ which was also coined in the paper that introduced the GELU.)

GELUs are used in GPT-3, BERT, and most other Transformers.

#### Papers

Paper Code Results Date Stars

Retrieval 91 10.69%
Language Modelling 71 8.34%
Large Language Model 44 5.17%
Text Generation 25 2.94%
In-Context Learning 21 2.47%
Sentence 20 2.35%
Information Retrieval 16 1.88%
Few-Shot Learning 15 1.76%

#### Components

Component Type
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