question about the dimension

[lrrll]

Traceback (most recent call last):
File "Train_PFNet.py", line 221, in
fake_center1,fake_center2,fake =point_netG(input_cropped)
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/modules/module.py", line 489, in call
result = self.forward(*input, **kwargs)
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/parallel/data_parallel.py", line 143, in forward
outputs = self.parallel_apply(replicas, inputs, kwargs)
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/parallel/data_parallel.py", line 153, in parallel_apply
return parallel_apply(replicas, inputs, kwargs, self.device_ids[:len(replicas)])
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/parallel/parallel_apply.py", line 83, in parallel_apply
raise output
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/parallel/parallel_apply.py", line 59, in _worker
output = module(*input, **kwargs)
File "/home/ouc/.conda/envs/PF-Net/lib/python3.7/site-packages/torch/nn/modules/module.py", line 489, in call
result = self.forward(*input, **kwargs)
File "/home/ouc/l-dataset/PF-Net-Point-Fractal-Network-master/model_PFNet.py", line 161, in forward
pc3_xyz = pc2_xyz_expand+pc3_xyz
RuntimeError: The size of tensor a (12) must match the size of tensor b (20) at non-singleton dimension 0

when i run the Tranin_PFNet.py it meet this problem,but i only change the epoch,could you please find the problem?