I want to realize VAR by pytorch, where for time shot t, Y[t]=W1Y[t-1]+W2Y[t-3]. The general part of my pytorch code is just like the below one：

```
f1=torch.nn.Linear(input_dim,output_dim)
f2=torch.nn.Linear(input_dim,output_dim)
for i in range(3,Y.shape[0]):
Y[i]=Y[i]+f1(Y[i-1])+f2(Y[i-3])
```

However, when I backward the loss function of Y, there became an error:

```
RuntimeError: one of the variables needed for gradient computation has been modified by an inplace operation: [torch.FloatTensor [1, 100]], which is output 0 of UnsqueezeBackward0, is at version 5040; expected version 5039 instead. Hint: the backtrace further above shows the operation that failed to compute its gradient. The variable in question was changed in there or anywhere later. Good luck!
```

Is there an easy way to realize VAR by pytorch? Thank you!