激活函数汇总，包含公式、求导过程以及numpy实现，妥妥的万字干货

悠悠 2022-09-11 09:19 227阅读 0赞

### 文章目录 ###

*  1、激活函数的实现
 *   *  1.1 sigmoid
     *   *  1.1.1 函数
         *  1.1.2 导数
         *  1.1.3 代码实现
     *  1.2 softmax
     *   *  1.2.1 函数
         *  1.2.2 导数
         *  1.2.3 代码实现
     *  1.3 tanh
     *   *  1.3.1 函数
         *  1.3.2 导数
         *  1.3.3 代码实现
     *  1.4 relu
     *   *  1.4.1 函数
         *  1.4.2 导数
         *  1.4.3 代码实现
     *  1.5 leakyrelu
     *   *  1.5.1 函数
         *  1.5.2 导数
         *  1.5.3 代码实现
     *  1.6 ELU
     *   *  1.61 函数
         *  1.6.2 导数
         *  1.6.3 代码实现
     *  1.7 selu
     *   *  1.7.1 函数
         *  1.7.2 导数
         *  1.7.3 代码实现
     *  1.8 softplus
     *   *  1.81 函数
         *  1.8.2 导数
         *  1.8.3 代码实现
 *  1.9 Swish
 *   *   *  1.9.1 函数
         *  1.9.2 导数
         *  1.9.3 代码实现
     *  1.10 Mish
     *   *  1.10.1 函数
         *  1.10.2 导数
         *  1.10.3 代码实现
     *  1.11 SiLU
     *   *  1.11.1 函数
         *  1.11.2 导数
         *  1.11.3 代码实现
     *  1.12 完整代码

# 1、激活函数的实现 #

## 1.1 sigmoid ##

### 1.1.1 函数 ###

函数： f ( x ) = 1 1 + e − x f(x)=\\frac\{1\}\{1+e^\{-x\}\} f(x)=1\+e−x1

![img][]

### 1.1.2 导数 ###

求导过程：

根据： ( u v ) ′ = u ′ v − u v ′ v 2 \\left ( \\frac\{u\}\{v\} \\right )\{\}'=\\frac\{ \{u\}'v-u\{v\}'\}\{v^\{2\}\} (vu)′=v2u′v−uv′  
 f ( x ) ′ = ( 1 1 + e − x ) ′ = 1 ′ × ( 1 + e − x ) − 1 × ( 1 + e − x ) ′ ( 1 + e − x ) 2 = e − x ( 1 + e − x ) 2 = 1 + e − x − 1 ( 1 + e − x ) 2 = ( 1 1 + e − x ) ( 1 − 1 1 + e − x ) = f ( x ) ( 1 − f ( x ) ) \\begin\{aligned\} f(x)^\{\\prime\} &=\\left(\\frac\{1\}\{1+e^\{-x\}\}\\right)^\{\\prime\} \\\\ &=\\frac\{1^\{\\prime\} \\times\\left(1+e^\{-x\}\\right)-1 \\times\\left(1+e^\{-x\}\\right)^\{\\prime\}\}\{\\left(1+e^\{-x\}\\right)^\{2\}\} \\\\ &=\\frac\{e^\{-x\}\}\{\\left(1+e^\{-x\}\\right)^\{2\}\} \\\\ &=\\frac\{1+e^\{-x\}-1\}\{\\left(1+e^\{-x\}\\right)^\{2\}\} \\\\ &=\\left(\\frac\{1\}\{1+e^\{-x\}\}\\right)\\left(1-\\frac\{1\}\{1+e^\{-x\}\}\\right) \\\\ &=\\quad f(x)(1-f(x)) \\end\{aligned\} f(x)′=(1\+e−x1)′=(1\+e−x)21′×(1\+e−x)−1×(1\+e−x)′=(1\+e−x)2e−x=(1\+e−x)21\+e−x−1=(1\+e−x1)(1−1\+e−x1)=f(x)(1−f(x))

![img][img 1]

### 1.1.3 代码实现 ###

import numpy as np
    
    class Sigmoid():
        def __call__(self, x):
            return 1 / (1 + np.exp(-x))
    
        def gradient(self, x):
            return self.__call__(x) * (1 - self.__call__(x))

## 1.2 softmax ##

### 1.2.1 函数 ###

softmax用于多分类过程中，它将多个神经元的输出，映射到（0,1）区间内，可以看成概率来理解，从而来进行多分类！

假设我们有一个数组，V，Vi表示V中的第i个元素，那么这个元素的softmax值就是:  
 S i = e i ∑ j e j S\_\{i\}=\\frac\{e^\{i\}\}\{\\sum \_\{j\}e^\{j\}\} Si=∑jejei  
更形象的如下图表示：

![1180120-20180520190635891-1537309048][]  
 y 1 = e z 1 e z 1 + e z 2 + e z 3 y 2 = e z 2 e z 1 + e z 2 + e z 3 y 3 = e z 3 e z 1 + e z 2 + e z 3 (1) y1=\\frac\{e^\{z\_\{1\}\}\}\{e^\{z\_\{1\}\}+e^\{z\_\{2\}\}+e^\{z\_\{3\}\}\}\\\\ y2=\\frac\{e^\{z\_\{2\}\}\}\{e^\{z\_\{1\}\}+e^\{z\_\{2\}\}+e^\{z\_\{3\}\}\}\\\\ y3=\\frac\{e^\{z\_\{3\}\}\}\{e^\{z\_\{1\}\}+e^\{z\_\{2\}\}+e^\{z\_\{3\}\}\}\\\\ \\tag\{1\} y1=ez1\+ez2\+ez3ez1y2=ez1\+ez2\+ez3ez2y3=ez1\+ez2\+ez3ez3(1)  
要使用梯度下降，就需要一个损失函数，一般使用交叉熵作为损失函数，交叉熵函数形式如下：  
 L o s s = − ∑ i y i l n a i (2) Loss = -\\sum\_\{i\}^\{\}\{y\_\{i\}lna\_\{i\} \} \\tag\{2\} Loss=−i∑yilnai(2)

### 1.2.2 导数 ###

求导分为两种情况。

第一种j=i：  
 S i = e i ∑ j e j = e i ∑ i e i S\_\{i\}=\\frac\{e^\{i\}\}\{\\sum \_\{j\}e^\{j\}\}=\\frac\{e^\{i\}\}\{\\sum \_\{i\}e^\{i\}\} Si=∑jejei=∑ieiei  
推导过程如下：  
 f ′ = ( e i ∑ i e i ) ′ = ( e i ) × ∑ i e i − e i × e i ( ∑ i e i ) 2 = e i ∑ i e i − e i ∑ i e i × e i ∑ i e i = e i ∑ i e i ( 1 − e i ∑ i e i ) = f ( 1 − f ) \\begin\{aligned\} f^\{\\prime\}&=\\left(\\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\}\\right)^\{\\prime\} & \\\\ &=\\frac\{\\left(e^\{i\}\\right) \\times \\sum\_\{i\} e^\{i\}-e^\{i\} \\times e^\{i\}\}\{\\left(\\sum\_\{i\} e^\{i\}\\right)^\{2\}\} \\\\ &=\\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\}-\\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\} \\times \\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\} \\\\ &= \\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\}\\left(1-\\frac\{e^\{i\}\}\{\\sum\_\{i\} e^\{i\}\}\\right) \\\\ &= f(1-f) \\end\{aligned\} f′=(∑ieiei)′=(∑iei)2(ei)×∑iei−ei×ei=∑ieiei−∑ieiei×∑ieiei=∑ieiei(1−∑ieiei)=f(1−f)

### 1.2.3 代码实现 ###

import numpy as np
    class Softmax():
        def __call__(self, x):
            e_x = np.exp(x - np.max(x, axis=-1, keepdims=True))
            return e_x / np.sum(e_x, axis=-1, keepdims=True)
    
        def gradient(self, x):
            p = self.__call__(x)
            return p * (1 - p)

## 1.3 tanh ##

### 1.3.1 函数 ###

t a n h ( x ) = e x − e − x e x + e − x tanh(x)=\\frac\{e^\{x\}-e^\{-x\}\}\{e^\{x\}+e^\{-x\}\} tanh(x)=ex\+e−xex−e−x

![img][img 2]

### 1.3.2 导数 ###

求导过程：  
 tanh ⁡ ( x ) ′ = ( e x − e − x e x + e − x ) ′ = ( e x − e − x ) ′ ( e x + e − x ) − ( e x − e − x ) ( e x + e − x ) ′ ( e x + e − x ) 2 = ( e x + e − x ) 2 − ( e x ⋅ e − x ) 2 ( e x + e − x ) 2 = 1 − ( e x − e − x e x + e − x ) 2 = 1 − tanh ⁡ ( x ) 2 \\begin\{aligned\} \\tanh (x)^\{\\prime\} &=\\left(\\frac\{e^\{x\}-e^\{-x\}\}\{e^\{x\}+e^\{-x\}\}\\right)^\{\\prime\} \\\\ &=\\frac\{\\left(e^\{x\}-e^\{-x\}\\right)^\{\\prime\}\\left(e^\{x\}+e^\{-x\}\\right)-\\left(e^\{x\}-e^\{-x\}\\right)\\left(e^\{x\}+e^\{-x\}\\right)^\{\\prime\}\}\{\\left(e^\{x\}+e^\{-x\}\\right)^\{2\}\} \\\\ &=\\frac\{\\left(e^\{x\}+e^\{-x\}\\right)^\{2\}-\\left(e^\{x\} \\cdot e^\{-x\}\\right)^\{2\}\}\{\\left(e^\{x\}+e^\{-x\}\\right)^\{2\}\} \\\\ &=1-\\left(\\frac\{e^\{x\}-e^\{-x\}\}\{e^\{x\}+e^\{-x\}\}\\right)^\{2\} \\\\ &=1-\\tanh (x)^\{2\} \\end\{aligned\} tanh(x)′=(ex\+e−xex−e−x)′=(ex\+e−x)2(ex−e−x)′(ex\+e−x)−(ex−e−x)(ex\+e−x)′=(ex\+e−x)2(ex\+e−x)2−(ex⋅e−x)2=1−(ex\+e−xex−e−x)2=1−tanh(x)2

### 1.3.3 代码实现 ###

import numpy as np
    class TanH():
        def __call__(self, x):
            return 2 / (1 + np.exp(-2*x)) - 1
    
        def gradient(self, x):
            return 1 - np.power(self.__call__(x), 2)

## 1.4 relu ##

### 1.4.1 函数 ###

f ( x ) = max ⁡ ( 0 , x ) f(x)=\\max (0, x) f(x)=max(0,x)

### 1.4.2 导数 ###

f ′ ( x ) = \{ 1  if  ( x > 0 ) 0  if  ( x < = 0 ) f^\{\\prime\}(x)=\\left\\\{\\begin\{array\}\{cc\} 1 & \\text \{ if \} (x>0) \\\\ 0 & \\text \{ if \} (x<=0) \\end\{array\}\\right. f′(x)=\{ 10 if (x>0) if (x<=0)

### 1.4.3 代码实现 ###

import numpy as np
    class ReLU():
        def __call__(self, x):
            return np.where(x >= 0, x, 0)
    
        def gradient(self, x):
            return np.where(x >= 0, 1, 0)

## 1.5 leakyrelu ##

### 1.5.1 函数 ###

f ( x ) = max ⁡ ( a x , x ) f(x)=\\max (a x, x) f(x)=max(ax,x)

### 1.5.2 导数 ###

f ′ ( x ) = \{ 1  if  ( x > 0 ) a  if  ( x < = 0 ) f^\{\\prime\}(x)=\\left\\\{\\begin\{array\}\{cl\} 1 & \\text \{ if \} (x>0) \\\\ a & \\text \{ if \}(x<=0) \\end\{array\}\\right. f′(x)=\{ 1a if (x>0) if (x<=0)

### 1.5.3 代码实现 ###

import numpy as np
    class LeakyReLU():
        def __init__(self, alpha=0.2):
            self.alpha = alpha
    
        def __call__(self, x):
            return np.where(x >= 0, x, self.alpha * x)
    
        def gradient(self, x):
            return np.where(x >= 0, 1, self.alpha)

## 1.6 ELU ##

### 1.61 函数 ###

f ( x ) = \{ x ,  if  x ≥ 0 a ( e x − 1 ) ,  if  ( x < 0 ) f(x)=\\left\\\{\\begin\{array\}\{cll\} x, & \\text \{ if \} x \\geq 0 \\\\ a\\left(e^\{x\}-1\\right), & \\text \{ if \} (x<0) \\end\{array\}\\right. f(x)=\{ x,a(ex−1), if x≥0 if (x<0)

### 1.6.2 导数 ###

当x>=0时，导数为1。

当x<0时，导数的推导过程：  
 f ( x ) ′ = ( a ( e x − 1 ) ) ′ = a e x = a ( e x − 1 ) + a = f ( x ) + a = a e x \\begin\{aligned\} \\\\ f(x)^\{\\prime\} &=\\left(a\\left(e^\{x\}-1\\right)\\right)^\{\\prime\} \\\\ &=a e^\{x\} \\\\ &\\left.=a (e^\{x\}-1\\right)+a \\\\ &=f(x)+a=ae^\{x\} \\end\{aligned\} f(x)′=(a(ex−1))′=aex=a(ex−1)\+a=f(x)\+a=aex  
所以，完整的导数为：  
 f ′ = \{ 1  if  x ≥ 0 f ( x ) + a = a e x  if  x < 0 f^\{\\prime\}=\\left\\\{\\begin\{array\}\{cll\} 1 & \\text \{ if \} & x \\geq 0 \\\\ f(x)+a=ae^\{x\} & \\text \{ if \} & x<0 \\end\{array\}\\right. f′=\{ 1f(x)\+a=aex if  if x≥0x<0

### 1.6.3 代码实现 ###

import numpy as np
    class ELU():
        def __init__(self, alpha=0.1):
            self.alpha = alpha 
    
        def __call__(self, x):
            return np.where(x >= 0.0, x, self.alpha * (np.exp(x) - 1))
    
        def gradient(self, x):
            return np.where(x >= 0.0, 1, self.__call__(x) + self.alpha)

## 1.7 selu ##

### 1.7.1 函数 ###

selu ⁡ ( x ) = λ \{ x  if  ( x > 0 ) α e x − α  if  ( x ⩽ 0 ) \\operatorname\{selu\}(x)=\\lambda \\begin\{cases\}x & \\text \{ if \} (x>0) \\\\ \\alpha e^\{x\}-\\alpha & \\text \{ if \} (x \\leqslant 0)\\end\{cases\} selu(x)=λ\{ xαex−α if (x>0) if (x⩽0)

### 1.7.2 导数 ###

selu ⁡ ′ ( x ) = λ \{ 1 x > 0 α e x ⩽ 0 \\operatorname\{selu\}^\{\\prime\}(x)=\\lambda \\begin\{cases\}1 & x>0 \\\\ \\alpha e^\{x\} & \\leqslant 0\\end\{cases\} selu′(x)=λ\{ 1αexx>0⩽0

### 1.7.3 代码实现 ###

import numpy as np
    class SELU():
        # Reference : https://arxiv.org/abs/1706.02515,
        # https://github.com/bioinf-jku/SNNs/blob/master/SelfNormalizingNetworks_MLP_MNIST.ipynb
        def __init__(self):
            self.alpha = 1.6732632423543772848170429916717
            self.scale = 1.0507009873554804934193349852946 
    
        def __call__(self, x):
            return self.scale * np.where(x >= 0.0, x, self.alpha*(np.exp(x)-1))
    
        def gradient(self, x):
            return self.scale * np.where(x >= 0.0, 1, self.alpha * np.exp(x))

## 1.8 softplus ##

### 1.81 函数 ###

Softplus ⁡ ( x ) = log ⁡ ( 1 + e x ) \\operatorname\{Softplus\}(x)=\\log \\left(1+e^\{x\}\\right) Softplus(x)=log(1\+ex)

### 1.8.2 导数 ###

log默认的底数是 e e e  
 f ′ ( x ) = e x ( 1 + e x ) ln ⁡ e = 1 1 + e − x = σ ( x ) f^\{\\prime\}(x)=\\frac\{e^\{x\}\}\{(1+e^\{x\})\\ln e\}=\\frac\{1\}\{1+e^\{-x\}\}=\\sigma(x) f′(x)=(1\+ex)lneex=1\+e−x1=σ(x)

### 1.8.3 代码实现 ###

import numpy as np
    class SoftPlus():
        def __call__(self, x):
            return np.log(1 + np.exp(x))
    
        def gradient(self, x):
            return 1 / (1 + np.exp(-x))

# 1.9 Swish #

### 1.9.1 函数 ###

f ( x ) = x ⋅ sigmoid ⁡ ( β x ) f(x)=x \\cdot \\operatorname\{sigmoid\}(\\beta x) f(x)=x⋅sigmoid(βx)

### 1.9.2 导数 ###

f ′ ( x ) = σ ( β x ) + β x ⋅ σ ( β x ) ( 1 − σ ( β x ) ) = σ ( β x ) + β x ⋅ σ ( β x ) − β x ⋅ σ ( β x ) 2 = β x ⋅ σ ( x ) + σ ( β x ) ( 1 − β x ⋅ σ ( β x ) ) = β f ( x ) + σ ( β x ) ( 1 − β f ( x ) ) \\begin\{aligned\} f^\{\\prime\}(x) &=\\sigma(\\beta x)+\\beta x \\cdot \\sigma(\\beta x)(1-\\sigma(\\beta x)) \\\\ &=\\sigma(\\beta x)+\\beta x \\cdot \\sigma(\\beta x)-\\beta x \\cdot \\sigma(\\beta x)^\{2\} \\\\ &=\\beta x \\cdot \\sigma(x)+\\sigma(\\beta x)(1-\\beta x \\cdot \\sigma(\\beta x)) \\\\ &=\\beta f(x)+\\sigma(\\beta x)(1-\\beta f(x)) \\end\{aligned\} f′(x)=σ(βx)\+βx⋅σ(βx)(1−σ(βx))=σ(βx)\+βx⋅σ(βx)−βx⋅σ(βx)2=βx⋅σ(x)\+σ(βx)(1−βx⋅σ(βx))=βf(x)\+σ(βx)(1−βf(x))

### 1.9.3 代码实现 ###

import numpy as np
    
    
    class Swish(object):
        def __init__(self, b):
            self.b = b
    
        def __call__(self, x):
            return x * (np.exp(self.b * x) / (np.exp(self.b * x) + 1))
    
        def gradient(self, x):
            return self.b * x / (1 + np.exp(-self.b * x)) + (1 / (1 + np.exp(-self.b * x)))(
                1 - self.b * (x / (1 + np.exp(-self.b * x))))

## 1.10 Mish ##

### 1.10.1 函数 ###

f ( x ) = x ∗ tanh ⁡ ( ln ⁡ ( 1 + e x ) ) f(x)=x \* \\tanh \\left(\\ln \\left(1+e^\{x\}\\right)\\right) f(x)=x∗tanh(ln(1\+ex))

### 1.10.2 导数 ###

f ′ ( x ) = sech ⁡ 2 ( soft ⁡ plus ⁡ ( x ) ) x sigmoid ⁡ ( x ) + f ( x ) x = Δ ( x ) s w i sh ⁡ ( x ) + f ( x ) x \\begin\{gathered\} f^\{\\prime\}(x)=\\operatorname\{sech\}^\{2\}(\\operatorname\{soft\} \\operatorname\{plus\}(x)) x \\operatorname\{sigmoid\}(x)+\\frac\{f(x)\}\{x\} \\\\ =\\Delta(x) s w i \\operatorname\{sh\}(x)+\\frac\{f(x)\}\{x\} \\end\{gathered\} f′(x)=sech2(softplus(x))xsigmoid(x)\+xf(x)=Δ(x)swish(x)\+xf(x)  
where softplus  ( x ) = ln ⁡ ( 1 + e x ) (x)=\\ln \\left(1+e^\{x\}\\right) (x)=ln(1\+ex) and sigmoid  ( x ) = 1 / ( 1 + e − x ) (x)=1 /\\left(1+e^\{-x\}\\right) (x)=1/(1\+e−x).

### 1.10.3 代码实现 ###

import numpy as np
    
    
    def sech(x):
        """sech函数"""
        return 2 / (np.exp(x) + np.exp(-x))
    
    
    def sigmoid(x):
        """sigmoid函数"""
        return 1 / (1 + np.exp(-x))
    
    
    def soft_plus(x):
        """softplus函数"""
        return np.log(1 + np.exp(x))
    
    
    def tan_h(x):
        """tanh函数"""
        return (np.exp(x) - np.exp(-x)) / (np.exp(x) + np.exp(-x))
    
    
    class Mish:
    
        def __call__(self, x):
            return x * tan_h(soft_plus(x))
    
        def gradient(self, x):
            return sech(soft_plus(x)) * sech(soft_plus(x)) * x * sigmoid(x) + tan_h(soft_plus(x))

## 1.11 SiLU ##

### 1.11.1 函数 ###

f ( x ) = x × s i g m o i d ( x ) f(x)=x \\times sigmoid (x) f(x)=x×sigmoid(x)

![img][img 3]

### 1.11.2 导数 ###

推导过程  
 f ( x ) ′ = ( x ⋅ s i g m o i d ( x ) ) ′ = s i g m o i d ( x ) + x ⋅ ( s i g m o i d ( x ) ( 1 − s i g m o i d ( x ) ) = s i g m o i d ( x ) + x ⋅ s i g m o i d ( x ) − x ⋅ s i g m o i d 2 ( x ) = f ( x ) + sigmoid ⁡ ( x ) ( 1 − f ( x ) ) \\begin\{aligned\} &f(x)^\{\\prime\}=(x \\cdot sigmoid(x))^\{\\prime\}\\\\ &=sigmoid(x)+x \\cdot(sigmoid(x)(1-sigmoid(x))\\\\ &=sigmoid(x)+x \\cdot sigmoid(x)-x \\cdot sigmoid^\{2\}(x)\\\\ &=f(x)+\\operatorname\{sigmoid\}(x)(1-f(x)) \\end\{aligned\} f(x)′=(x⋅sigmoid(x))′=sigmoid(x)\+x⋅(sigmoid(x)(1−sigmoid(x))=sigmoid(x)\+x⋅sigmoid(x)−x⋅sigmoid2(x)=f(x)\+sigmoid(x)(1−f(x))  
![img][img 4]

### 1.11.3 代码实现 ###

import numpy as np
    
    
    def sigmoid(x):
        """sigmoid函数"""
        return 1 / (1 + np.exp(-x))
    
    
    class SILU(object):
    
        def __call__(self, x):
            return x * sigmoid(x)
    
        def gradient(self, x):
            return self.__call__(x) + sigmoid(x) * (1 - self.__call__(x))

## 1.12 完整代码 ##

定义一个activation\_function.py,将下面的代码复制进去，到这里激活函数就完成了。

import numpy as np
    
    
    # Collection of activation functions
    # Reference: https://en.wikipedia.org/wiki/Activation_function
    
    class Sigmoid():
        def __call__(self, x):
            return 1 / (1 + np.exp(-x))
    
        def gradient(self, x):
            return self.__call__(x) * (1 - self.__call__(x))
    
    
    class Softmax():
        def __call__(self, x):
            e_x = np.exp(x - np.max(x, axis=-1, keepdims=True))
            return e_x / np.sum(e_x, axis=-1, keepdims=True)
    
        def gradient(self, x):
            p = self.__call__(x)
            return p * (1 - p)
    
    
    class TanH():
        def __call__(self, x):
            return 2 / (1 + np.exp(-2 * x)) - 1
    
        def gradient(self, x):
            return 1 - np.power(self.__call__(x), 2)
    
    
    class ReLU():
        def __call__(self, x):
            return np.where(x >= 0, x, 0)
    
        def gradient(self, x):
            return np.where(x >= 0, 1, 0)
    
    
    class LeakyReLU():
        def __init__(self, alpha=0.2):
            self.alpha = alpha
    
        def __call__(self, x):
            return np.where(x >= 0, x, self.alpha * x)
    
        def gradient(self, x):
            return np.where(x >= 0, 1, self.alpha)
    
    
    class ELU(object):
        def __init__(self, alpha=0.1):
            self.alpha = alpha
    
        def __call__(self, x):
            return np.where(x >= 0.0, x, self.alpha * (np.exp(x) - 1))
    
        def gradient(self, x):
            return np.where(x >= 0.0, 1, self.__call__(x) + self.alpha)
    
    
    class SELU():
        # Reference : https://arxiv.org/abs/1706.02515,
        # https://github.com/bioinf-jku/SNNs/blob/master/SelfNormalizingNetworks_MLP_MNIST.ipynb
        def __init__(self):
            self.alpha = 1.6732632423543772848170429916717
            self.scale = 1.0507009873554804934193349852946
    
        def __call__(self, x):
            return self.scale * np.where(x >= 0.0, x, self.alpha * (np.exp(x) - 1))
    
        def gradient(self, x):
            return self.scale * np.where(x >= 0.0, 1, self.alpha * np.exp(x))
    
    
    class SoftPlus(object):
        def __call__(self, x):
            return np.log(1 + np.exp(x))
    
        def gradient(self, x):
            return 1 / (1 + np.exp(-x))
    
    
    class Swish(object):
        def __init__(self, b):
            self.b = b
    
        def __call__(self, x):
            return x * (np.exp(self.b * x) / (np.exp(self.b * x) + 1))
    
        def gradient(self, x):
            return self.b * x / (1 + np.exp(-self.b * x)) + (1 / (1 + np.exp(-self.b * x)))(
                1 - self.b * (x / (1 + np.exp(-self.b * x))))
    
    
    def sech(x):
        """sech函数"""
        return 2 / (np.exp(x) + np.exp(-x))
    
    
    def sigmoid(x):
        """sigmoid函数"""
        return 1 / (1 + np.exp(-x))
    
    
    def soft_plus(x):
        """softplus函数"""
        return np.log(1 + np.exp(x))
    
    
    def tan_h(x):
        """tanh函数"""
        return (np.exp(x) - np.exp(-x)) / (np.exp(x) + np.exp(-x))
    
    
    class Mish:
    
        def __call__(self, x):
            return x * tan_h(soft_plus(x))
    
        def gradient(self, x):
            return sech(soft_plus(x)) * sech(soft_plus(x)) * x * sigmoid(x) + tan_h(soft_plus(x))
    
    class SILU(object):
    
        def __call__(self, x):
            return x * sigmoid(x)
    
        def gradient(self, x):
            return self.__call__(x) + sigmoid(x) * (1 - self.__call__(x))

参考公式  
 ( C ) ′ = 0 (C)^\{\\prime\}=0 (C)′=0  
 ( a x ) ′ = a x ln ⁡ a \\left(a^\{x\}\\right)^\{\\prime\}=a^\{x\} \\ln a (ax)′=axlna  
 ( x μ ) ′ = μ x μ − 1 \\left(x^\{\\mu\}\\right)^\{\\prime\}=\\mu x^\{\\mu-1\} (xμ)′=μxμ−1  
 ( e x ) ′ = e x \\left(e^\{x\}\\right)^\{\\prime\}=e^\{x\} (ex)′=ex  
 ( sin ⁡ x ) ′ = cos ⁡ x (\\sin x)^\{\\prime\}=\\cos x (sinx)′=cosx  
 ( log ⁡ a x ) ′ = 1 x ln ⁡ a \\left(\\log \_\{a\} x\\right)^\{\\prime\}=\\frac\{1\}\{x \\ln a\} (logax)′=xlna1  
 ( cos ⁡ x ) ′ = − sin ⁡ x (\\cos x)^\{\\prime\}=-\\sin x (cosx)′=−sinx  
 ( ln ⁡ x ) ′ = 1 x (\\ln x)^\{\\prime\}=\\frac\{1\}\{x\} (lnx)′=x1  
 ( tan ⁡ x ) ′ = sec ⁡ 2 x (\\tan x)^\{\\prime\}=\\sec ^\{2\} x (tanx)′=sec2x  
 ( arcsin ⁡ x ) ′ = 1 1 − x 2 (\\arcsin x)^\{\\prime\}=\\frac\{1\}\{\\sqrt\{1-x^\{2\}\}\} (arcsinx)′=1−x21  
 ( cot ⁡ x ) ′ = − csc ⁡ 2 x (\\cot x)^\{\\prime\}=-\\csc ^\{2\} x (cotx)′=−csc2x  
 ( arccos ⁡ x ) ′ = − 1 1 − x 2 (\\arccos x)^\{\\prime\}=-\\frac\{1\}\{\\sqrt\{1-x^\{2\}\}\} (arccosx)′=−1−x21  
 ( sec ⁡ x ) ′ = sec ⁡ x ⋅ tan ⁡ x (\\sec x)^\{\\prime\}=\\sec x \\cdot \\tan x (secx)′=secx⋅tanx  
 ( arctan ⁡ x ) ′ = 1 1 + x 2 (\\arctan x)^\{\\prime\}=\\frac\{1\}\{1+x^\{2\}\} (arctanx)′=1\+x21  
 ( csc ⁡ x ) ′ = − csc ⁡ x ⋅ cot ⁡ x (\\csc x)^\{\\prime\}=-\\csc x \\cdot \\cot x (cscx)′=−cscx⋅cotx  
 ( arccot ⁡ x ) ′ = − 1 1 + x 2 (\\operatorname\{arccot\} x)^\{\\prime\}=-\\frac\{1\}\{1+x^\{2\}\} (arccotx)′=−1\+x21

双曲正弦:  sinh ⁡ x = e x − e − x 2 \\sinh x=\\frac\{e^\{x\}-e^\{-x\}\}\{2\} sinhx=2ex−e−x  
双曲余弦:  cosh ⁡ x = e x + e − x 2 \\cosh x=\\frac\{e^\{x\}+e^\{-x\}\}\{2\} coshx=2ex\+e−x  
双曲正切:  tanh ⁡ x = sinh ⁡ x cosh ⁡ x = e x − e − x e x + e − x \\tanh x=\\frac\{\\sinh x\}\{\\cosh x\}=\\frac\{e^\{x\}-e^\{-x\}\}\{e^\{x\}+e^\{-x\}\} tanhx=coshxsinhx=ex\+e−xex−e−x  
双曲余切:  coth ⁡ x = 1 tanh ⁡ x = e x + e − x e x − e − x \\operatorname\{coth\} x=\\frac\{1\}\{\\tanh x\}=\\frac\{e^\{x\}+e^\{-x\}\}\{e^\{x\}-e^\{-x\}\} cothx=tanhx1=ex−e−xex\+e−x  
双曲正割：  sech ⁡ x = 1 cosh ⁡ x = 2 e x + e − x \\operatorname\{sech\} x=\\frac\{1\}\{\\cosh x\}=\\frac\{2\}\{e^\{x\}+e^\{-x\}\} sechx=coshx1=ex\+e−x2  
双曲余割：  csch ⁡ x = 1 sinh ⁡ x = 2 e x − e − x \\operatorname\{csch\} x=\\frac\{1\}\{\\sinh x\}=\\frac\{2\}\{e^\{x\}-e^\{-x\}\} cschx=sinhx1=ex−e−x2

[img]: /images/20220828/19d2305c602b47efba771857da1e7bc1.png
[img 1]: /images/20220828/b135ac2a5e5e48d692c038f8c4bcc8cd.png
[1180120-20180520190635891-1537309048]: /images/20220828/db3c6e5cc38541cfb3cd177f9373320c.png
[img 2]: /images/20220828/8c789e14f1f74fb68423323209409886.png
[img 3]: /images/20220828/764c14a1703c4fb9a8c3520e8f458275.png
[img 4]: /images/20220828/a6d5d86590994eb3b61d79b599591a7f.png