python的pso优化bp神经网络
时间: 2023-09-11 14:06:25 浏览: 105
使用PSO算法优化BP神经网络的一般步骤如下:
1. 定义适应度函数:适应度函数可以使用BP神经网络的误差作为适应度函数,也可以使用其他的适应度函数。
2. 初始化粒子群:粒子群的每个粒子表示一组BP神经网络的参数。
3. 粒子位置更新:根据PSO算法公式,更新粒子位置,即更新BP神经网络的参数。
4. 计算适应度:计算每个粒子的适应度,即计算每组BP神经网络参数的误差。
5. 更新个体最优解和全局最优解:根据每个粒子的适应度,更新每个粒子的个体最优解和全局最优解。
6. 判断停止条件:如果满足停止条件,则输出最终的BP神经网络参数。
7. 回到第3步,继续更新粒子位置,直到满足停止条件。
下面是一个使用PSO算法优化BP神经网络的Python代码示例:
```python
import numpy as np
import random
#定义BP神经网络的类
class BPNet:
def __init__(self):
self.input_n = 0
self.hidden_n = 0
self.output_n = 0
self.input_weights = None
self.output_weights = None
#sigmoid函数
def sigmoid(self, x):
return 1.0 / (1.0 + np.exp(-x))
#初始化BP神经网络
def init(self, input_n, hidden_n, output_n):
self.input_n = input_n
self.hidden_n = hidden_n
self.output_n = output_n
self.input_weights = np.random.uniform(-0.5, 0.5, (self.input_n, self.hidden_n))
self.output_weights = np.random.uniform(-0.5, 0.5, (self.hidden_n, self.output_n))
#前向传播
def forward(self, inputs):
hidden_inputs = np.dot(inputs, self.input_weights)
hidden_outputs = self.sigmoid(hidden_inputs)
output_inputs = np.dot(hidden_outputs, self.output_weights)
output_outputs = self.sigmoid(output_inputs)
return output_outputs
#定义PSO算法的类
class PSO:
def __init__(self, fitness_func, dim, swarm_size, max_iter, x_min, x_max, v_min, v_max, c1, c2, w):
self.fitness_func = fitness_func
self.dim = dim
self.swarm_size = swarm_size
self.max_iter = max_iter
self.x_min = x_min
self.x_max = x_max
self.v_min = v_min
self.v_max = v_max
self.c1 = c1
self.c2 = c2
self.w = w
self.swarm = []
self.best_swarm_pos = None
self.best_swarm_fitness = float("inf")
self.init_swarm()
#初始化粒子群
def init_swarm(self):
for i in range(self.swarm_size):
pos = np.random.uniform(self.x_min, self.x_max, self.dim)
vel = np.random.uniform(self.v_min, self.v_max, self.dim)
fitness = self.fitness_func(pos)
self.swarm.append((pos, vel, fitness))
if fitness < self.best_swarm_fitness:
self.best_swarm_pos = pos
self.best_swarm_fitness = fitness
#更新粒子位置
def update_pos(self, i):
pos, vel, fitness = self.swarm[i]
new_vel = self.w * vel + self.c1 * random.random() * (self.best_swarm_pos - pos) + self.c2 * random.random() * (self.swarm[i][2] - pos)
new_vel = np.maximum(np.minimum(new_vel, self.v_max), self.v_min)
new_pos = pos + new_vel
new_pos = np.maximum(np.minimum(new_pos, self.x_max), self.x_min)
fitness = self.fitness_func(new_pos)
self.swarm[i] = (new_pos, new_vel, fitness)
if fitness < self.best_swarm_fitness:
self.best_swarm_pos = new_pos
self.best_swarm_fitness = fitness
#运行PSO算法
def run(self):
for i in range(self.max_iter):
for j in range(self.swarm_size):
self.update_pos(j)
print("Iteration: %d, Best Fitness: %f" % (i+1, self.best_swarm_fitness))
#定义适应度函数
def fitness_func(params):
input_n = 2
hidden_n = 4
output_n = 1
bpnet = BPNet()
bpnet.init(input_n, hidden_n, output_n)
bpnet.input_weights = np.reshape(params[:input_n*hidden_n], (input_n, hidden_n))
bpnet.output_weights = np.reshape(params[input_n*hidden_n:], (hidden_n, output_n))
inputs = np.array([[0, 0], [0, 1], [1, 0], [1, 1]])
targets = np.array([[0], [1], [1], [0]])
outputs = bpnet.forward(inputs)
error = np.sum((outputs - targets) ** 2)
return error
#运行PSO算法
swarm_size = 20
max_iter = 100
dim = (2+1)*4 + (4+1)*1
x_min = -1
x_max = 1
v_min = -0.1
v_max = 0.1
c1 = 2
c2 = 2
w = 0.5
pso = PSO(fitness_func, dim, swarm_size, max_iter, x_min, x_max, v_min, v_max, c1, c2, w)
pso.run()
```
在上述代码中,我们定义了一个BPNet类来实现BP神经网络,定义了一个PSO类来实现PSO算法,定义了fitness_func函数作为适应度函数,然后使用PSO算法来优化BP神经网络的参数。
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