错误：
RuntimeError: multi-target not supported at /pytorch/torch/lib/THCUNN/generic/ClassNLLCriterion.cu
错误反馈：
File "/users4/zsun/pytorch/paper_image_caption/sz-spatial5-chunk/model_msoft_gh.py", line 214, in forward
loss += F.cross_entropy( scores, captions.index_select(1, Variable(self.num_step_id+1)) )
File "/users4/zsun/anaconda3/lib/python3.6/site-packages/torch/nn/functional.py", line 1140, in cross_entropy
return nll_loss(log_softmax(input, 1), target, weight, size_average, ignore_index, reduce)
File "/users4/zsun/anaconda3/lib/python3.6/site-packages/torch/nn/functional.py", line 1049, in nll_loss
return torch._C._nn.nll_loss(input, target, weight, size_average, ignore_index, reduce)
RuntimeError: multi-target not supported at /pytorch/torch/lib/THCUNN/generic/ClassNLLCriterion.cu:16
出错代码：
loss += F.cross_entropy( scores, captions )
出错原因：
scores, captions的维度与F.cross_entropy()函数要求的维度不匹配，
例如出错的维度为scores=[batch, vocab_size], captions=[batch, 1]
解决：
loss += F.cross_entropy( scores, captions.squeeze() )