activations
时间: 2023-08-12 15:08:24 浏览: 55
在深度学习中,激活函数用于引入非线性性质,以增加模型的表达能力。目前最流行的激活函数是ReLU,它在正数范围内保持线性增长,而在负数范围内输出为零。[1]除了ReLU,还有一些新推出的激活函数,如swish、GELU和Mish,据称它们在某些情况下效果优于ReLU。[1][2][3]
Sigmoid是一种常用的激活函数,它将实数压缩到0到1之间,主要用于二分类的最后输出层。然而,Sigmoid存在梯度消失问题,计算复杂度较高,并且输出不以0为中心。[1]
Swish是由谷歌提出的自门控激活函数,相关研究表明,用Swish替代ReLU可以获得轻微的效果提升。[2]
GELU是一种高斯误差线性单元激活函数,在Transformer中表现最好。它能够避免梯度消失问题,并在tf-nightly包中得到支持。[2]
Mish是在YOLO v4中使用的激活函数,YOLO v4中还提到了其他激活函数,如Leaky ReLU、PReLU、ReLU6、SELU和Swish。其中,Leaky ReLU和PReLU在训练过程中可能较难优化,ReLU6则用于量化网络设计。[3]
相关问题
matlab activations
Matlab provides various functions to compute and analyze activations in neural networks. The most commonly used function is `activations()`, which calculates the output of a specific layer for a given input.
The syntax for `activations()` is as follows:
```matlab
output = activations(net, input, layer)
```
- `net` is the trained neural network model.
- `input` is the input data for which you want to calculate the activations.
- `layer` is the name or index of the specific layer whose activations you want to compute.
Here's an example that illustrates the usage of `activations()`:
```matlab
% Load a pretrained network (e.g., AlexNet)
net = alexnet;
% Generate a random input
input = randn(227, 227, 3);
% Compute activations for the 8th layer
layer = 'fc7';
output = activations(net, input, layer);
```
In this example, `output` will contain the activations of the 'fc7' layer for the given random input.
You can explore more functions provided by Matlab's Deep Learning Toolbox for activation analysis, such as `activationsGradient()`, `deepDreamImage()`, and `deepDreamVisualization()`. These functions allow you to analyze and visualize activations in greater detail.
activations.py代码
以下是一个简单的 activations.py 代码示例,其中包含了几个常见的激活函数(ReLU、sigmoid、tanh)的实现:
```
import numpy as np
def relu(Z):
"""
ReLU 激活函数
"""
return np.maximum(0, Z)
def sigmoid(Z):
"""
sigmoid 激活函数
"""
return 1 / (1 + np.exp(-Z))
def tanh(Z):
"""
tanh 激活函数
"""
return np.tanh(Z)
```
在这个示例中,我们使用 numpy 库实现了这些激活函数。在实际使用中,我们可以将这个文件导入到我们的神经网络实现中,并在定义层时指定激活函数。例如,如果我们想在某一层使用 ReLU 激活函数,我们可以这样写:
```
class DenseLayer:
def __init__(self, input_size, output_size, activation='relu'):
self.weights = ...
self.bias = ...
if activation == 'relu':
self.activation_function = relu
elif activation == 'sigmoid':
self.activation_function = sigmoid
elif activation == 'tanh':
self.activation_function = tanh
else:
raise ValueError("Invalid activation function: {}".format(activation))
...
```
这样,我们就可以在定义每一层时选择不同的激活函数了。