(单选题, 2.0 分)
关于 PyTorch 中 TransformerEncoder 的使用,以下代码执行后,output 的形状是?import torch
from torch.nn import TransformerEncoder, TransformerEncoderLayer
d_model = 64
nhead = 4
num_layers = 2
batch_size = 16
seq_len = 20
# 定义编码器层
encoder_layer = TransformerEncoderLayer(d_model=d_model, nhead=nhead, batch_first=True)
encoder = TransformerEncoder(encoder_layer, num_layers=num_layers)
# 输入张量 (batch_size, seq_len, d_model)
src = torch.randn(batch_size, seq_len, d_model)
output = encoder(src)
print(output.shape)