```python
import numpy as np
import tensorflow as tf
# 定义数据集
data = "hello world"
# 建立字符映射表
char_set = list(set(data))
char_dic = {w: i for i, w in enumerate(char_set)}
# 定义超参数
data_dim = len(char_set)
hidden_size = len(char_set)
num_classes = len(char_set)
sequence_length = len(data) - 1 # 序列长度为待预测字符数量
# 将数据转换为数字,以便于输入到神经网络
dataX = []
dataY = []
for i in range(0, len(data) - sequence_length):
x_str = data[i:i + sequence_length]
y_str = data[i + 1:i + sequence_length + 1]
x = [char_dic[c] for c in x_str]
y = [char_dic[c] for c in y_str]
dataX.append(x)
dataY.append(y)
# 转化为张量
batch_size = len(dataX)
input_batch = tf.convert_to_tensor(dataX)
output_batch = tf.one_hot(tf.convert_to_tensor(dataY), num_classes)
# 定义 RNN 模型
model = tf.keras.Sequential([
tf.keras.layers.Embedding(input_dim=data_dim, output_dim=hidden_size),
tf.keras.layers.LSTM(units=hidden_size, return_sequences=True),
tf.keras.layers.Dense(units=num_classes, activation='softmax')
])
# 定义优化器和损失函数
optimizer = tf.keras.optimizers.Adam()
loss = tf.keras.losses.CategoricalCrossentropy()
# 定义训练过程
@tf.function
def train_step(x, y):
with tf.GradientTape() as tape:
predictions = model(x)
cost = loss(y, predictions)
grads = tape.gradient(cost, model.trainable_variables)
optimizer.apply_gradients(zip(grads, model.trainable_variables))
return cost
# 训练模型
epochs = 100
for epoch in range(epochs):
total_cost = 0
for i in range(batch_size):
cost = train_step(input_batch[i:i+1], output_batch[i:i+1])
total_cost += cost
print('Epoch:', '%04d' % (epoch + 1), 'Avg. cost =', '{:.6f}'.format(total_cost / batch_size))
# 使用模型生成预测序列
def generate_text(model, char_dic, start_string):
num_generate = 10 # 预测字符数目
input_eval = [char_dic[s] for s in start_string]
input_eval = tf.expand_dims(input_eval, 0)
text_generated = []
model.reset_states()
for i in range(num_generate):
predictions = model(input_eval)
predictions = tf.squeeze(predictions, 0)
predicted_id = tf.random.categorical(predictions, num_samples=1)[-1,0].numpy()
input_eval = tf.expand_dims([predicted_id], 0)
text_generated.append(char_set[predicted_id])
return start_string + ''.join(text_generated)
print(generate_text(model, char_dic, start_string="h"))
```
以上代码中,我们建立了一个基于字符级别的自回归语言模型,其中 RNN 使用 LSTM 单元,并使用 CategoricalCrossentropy 损失函数进行训练。在训练完成后,我们可以使用该模型生成新的序列,例如从 "h" 开始,生成包含 10 个字符的序列。”