Hi there, I know this is a common error and there are many responses but I’ve read through them and I can’t find a fix. I’m trying to create what really should be a simple siamese network. I’ve successfully made them before. But I just can’t get around this error. I’ve gotten this error before and it usually means I tried to turn something into a numpy array in the middle of the network, but I can’t find where that’s happening here.

```
class ShearNet(nn.Module):
def __init__(self):
super(ShearNet, self).__init__()
self.fc = nn.Linear(100,10)
nn.Sequential(
nn.Linear(100, 10),
nn.Linear(10, 10),
nn.Linear(10, 2),
nn.Linear(2,1)
)
def forward(self, x):
output = self.fc(x)
return output
```

Before, I had this return the 2 outputs and it worked just fine. It’s only since asking the forward to find the cosine similarity that it won’t work. I think using functional inside a forward function shouldn’t cause any problems.

```
def __init__(self):
super(ShearShell, self).__init__()
self.shear_net = shear_net
def forward(self, x1, x2):
output1 = self.shear_net(x1)
output2 = self.shear_net(x2)
cosbt = F.cosine_similarity(x1,x2, dim=2)
output = torch.acos(cosbt)
return output
```

```
iteration_number = 0
for epoch in range(10):
for i, data in enumerate(train_data_loader,0):
embed0, embed1 = trainin
output = net(embed0, embed1)
#loss = lossfunc(output1, output2, trainout)
loss = criterion(output, trainout)
#loss.requires_grad = True
optimizer.zero_grad()
loss.backward()
optimizer.step()
```

```
RuntimeError Traceback (most recent call last)
<ipython-input-46-bfbbfb6b84c4> in <module>()
10 #loss.requires_grad = True
11 optimizer.zero_grad()
---> 12 loss.backward()
13 optimizer.step()
14 if (i %10 == 0 ):
1 frames
/usr/local/lib/python3.6/dist-packages/torch/autograd/__init__.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
97 Variable._execution_engine.run_backward(
98 tensors, grad_tensors, retain_graph, create_graph,
---> 99 allow_unreachable=True) # allow_unreachable flag
100
101
RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn
```

What am I missing??? Thank you!