请用keras编写一个全连接神经网络， 然后用遗传算法对神经网络的超参数进行优化，要优化的超参数包含每层的神经元个数，层数，学习率，激活函数，请写出代码

好的，这里是用Keras编写全连接神经网络并使用遗传算法对超参数进行优化的代码示例：

import numpy as np
import keras
from keras.models import Sequential
from keras.layers import Dense
from keras.optimizers import Adam
from keras.activations import relu, sigmoid, softmax
from keras.losses import binary_crossentropy, categorical_crossentropy
from keras.utils import to_categorical
from keras.callbacks import EarlyStopping

# Define the search space for hyperparameters
search_space = {
    'num_layers': [1, 2, 3],
    'num_neurons': [16, 32, 64],
    'learning_rate': [0.001, 0.01, 0.1],
    'activation': ['relu', 'sigmoid', 'softmax'],
}

# Define the fitness function for the genetic algorithm
def fitness_function(params):
    num_layers = params['num_layers']
    num_neurons = params['num_neurons']
    learning_rate = params['learning_rate']
    activation = params['activation']

    # Build the model
    model = Sequential()
    for i in range(num_layers):
        model.add(Dense(num_neurons, activation=activation))
    model.add(Dense(10, activation='softmax'))
    model.compile(optimizer=Adam(lr=learning_rate), loss=categorical_crossentropy, metrics=['accuracy'])

    # Train the model
    history = model.fit(X_train, y_train, validation_data=(X_val, y_val), epochs=100, batch_size=64, verbose=0,
                        callbacks=[EarlyStopping(patience=10, restore_best_weights=True)])

    # Evaluate the model on the test set
    score = model.evaluate(X_test, y_test, verbose=0)

    # Return the negative accuracy as the fitness value (since the genetic algorithm tries to minimize the fitness)
    return -score[1]

# Generate the initial population of solutions
population_size = 10
population = []
for i in range(population_size):
    params = {
        'num_layers': np.random.choice(search_space['num_layers']),
        'num_neurons': np.random.choice(search_space['num_neurons']),
        'learning_rate': np.random.choice(search_space['learning_rate']),
        'activation': np.random.choice(search_space['activation']),
    }
    population.append(params)

# Run the genetic algorithm for 10 generations
num_generations = 10
for i in range(num_generations):
    # Evaluate the fitness of the population
    fitness_values = [fitness_function(params) for params in population]

    # Select the parents for the next generation
    parent_indices = np.random.choice(population_size, size=2, replace=False, p=softmax(fitness_values))
    parents = [population[index] for index in parent_indices]

    # Generate the offspring using crossover and mutation
    offspring = []
    for j in range(population_size):
        child_params = {}
        for key in search_space.keys():
            parent_index = np.random.choice(len(parents))
            child_params[key] = parents[parent_index][key]
            if np.random.uniform() < 0.1:
                child_params[key] = np.random.choice(search_space[key])
        offspring.append(child_params)

    # Replace the population with the offspring
    population = offspring

# Evaluate the best solution found by the genetic algorithm
best_params = population[np.argmax(fitness_values)]
num_layers = best_params['num_layers']
num_neurons = best_params['num_neurons']
learning_rate = best_params['learning_rate']
activation = best_params['activation']

# Build and train the final model using the best hyperparameters
model = Sequential()
for i in range(num_layers):
    model.add(Dense(num_neurons, activation=activation))
model.add(Dense(10, activation='softmax'))
model.compile(optimizer=Adam(lr=learning_rate), loss=categorical_crossentropy, metrics=['accuracy'])
history = model.fit(X_train, y_train, validation_data=(X_val, y_val), epochs=100, batch_size=64)

这个代码示例首先定义了一个超参数搜索空间 `search_space`，包含了每层神经元个数、层数、学习率和激活函数等超参数。然后定义了一个适应度函数 `fitness_function`，它接受一个超参数字典作为输入，根据这些超参数构建一个全连接神经网络，训练并评估模型的性能，最后返回一个负的测试集准确率作为适应度值（因为遗传算法尝试最小化适应度）。

接着，代码生成了一个初始种群，大小为 `population_size`，每个个体都是一个超参数字典。然后运行了一个固定次数的遗传算法循环，每次循环中对种群中的个体进行评估、选择、交叉和变异，生成下一代种群。最终，代码返回了遗传算法搜索到的最优超参数，并使用这些超参数构建、训练和评估了一个最终的全连接神经网络模型。

需要注意的是，这个示例代码中的数据集和相关的代码实现并未给出，需要根据具体的任务和数据集进行修改。