During training a RNN-based model, there is a RuntimeError in loss.backward().
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File “/usr/local/lib/python2.7/dist-packages/torch/tensor.py”, line 102, in backward
torch.autograd.backward(self, gradient, retain_graph, create_graph)
File “/usr/local/lib/python2.7/dist-packages/torch/autograd/init.py”, line 90, in backward
allow_unreachable=True)  # allow_unreachable flag
RuntimeError: select(): index 10 out of range for tensor of size [10, 8, 12020] at dimension 0
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I wonder why such error appears at loss.backward().
The data flow is convinced to be correct because of the right forward().
How to debug such an error?