How to minimise loss with constrain in PyTorch? - deep-learning

Question

How to put constrain while minimising loss?
I am trying to minimise the mse loss with constrain loss but constrain was increasing instead of decreasing.then i tried to only minimise constrain then it throw following error.
class Edge_Detector(nn.Module):
def __init__(self,kernel_size,padding):
torch.manual_seed(1)
super(Edge_Detector,self).__init__()
self.sobelx=nn.Conv2d(1,1,kernel_size=kernel_size,padding=padding,bias=False)
self.relu=nn.ReLU()
self.sobely=nn.Conv2d(1,1,kernel_size=kernel_size,padding=padding,bias=False)
def forward(self,x):
x1=self.sobelx(x)
x2=self.sobely(x)
x=self.relu(x1+x2)
return x
def loss(self,x,y):
x=x.view(x.size(0),-1)
y=y.view(y.size(0),-1).float()
sobelx=self.sobelx.weight.data.squeeze().squeeze()
sobely=self.sobely.weight.data.squeeze().squeeze()
loss_mse=nn.MSELoss()(x,y)
loss_constrain=torch.matmul(sobelx,sobely.transpose(0,1)).trace()
#print('mse_loss : ',loss_mse)
#print('constrain_loss : ',loss_constrain)
#total_loss=loss_mse+loss_constrain
return loss_constrain
#Error Message:
RuntimeError Traceback (most recent call last)
<ipython-input-67-28b5b5719682> in <module>()
----> 1 learn.fit_one_cycle(15, 5e-2) #training for 4 epochs with lr=1e-3
13 frames
/usr/local/lib/python3.6/dist-packages/torch/autograd/__init__.py in backward(tensors, grad_tensors, retain_graph, create_graph, grad_variables)
130 Variable._execution_engine.run_backward(
131 tensors, grad_tensors_, retain_graph, create_graph,
--> 132 allow_unreachable=True) # allow_unreachable flag
133
134
RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn

Answer 1

Since you did not post the whole stack trace I can't say for sure, but I am pretty certain what happends is that you call backward on loss_constrain which throws an error because it has requires_grad=False. This is because in you calculation of loss_constrain you call the data attribute of the Parameter class (self.sobelx.weight), the parameter itself has requires_grad set to True but after calling data it is set to False.
Just remove the .data part and see whether it works