Hi
I am trying to integrate dice loss with my unet model, the dice is loss is borrowed from other task.This is what it looks like
    class GeneralizedDiceLoss(nn.Module):
        """Computes Generalized Dice Loss (GDL) as described in https://arxiv.org/pdf/1707.03237.pdf
        """

        def __init__(self, epsilon=1e-5, weight=None, ignore_index=None, sigmoid_normalization=True):
            super(GeneralizedDiceLoss, self).__init__()
            self.epsilon = epsilon
            self.register_buffer('weight', weight)
            self.ignore_index = ignore_index
            if sigmoid_normalization:
                self.normalization = nn.Sigmoid()
            else:
                self.normalization = nn.Softmax(dim=1)

        def forward(self, input, target):
            # get probabilities from logits
            input = input.float()
            input = self.normalization(input)

            assert input.size() == target.size(), "'input' and 'target' must have the same shape"

            # mask ignore_index if present
            if self.ignore_index is not None:
                mask = target.clone().ne_(self.ignore_index)
                mask.requires_grad = False

                input = input * mask
                target = target * mask

            input = flatten(input)
            target = flatten(target)

            target = target.float()
            target_sum = target.sum(-1)
            class_weights = Variable(1. / (target_sum * target_sum).clamp(min=self.epsilon), requires_grad=False)

            intersect = (input * target).sum(-1) * class_weights
            if self.weight is not None:
                weight = Variable(self.weight, requires_grad=False)
                intersect = weight * intersect
            intersect = intersect.sum()

            denominator = ((input + target).sum(-1) * class_weights).sum()

            return 1. - 2. * intersect / denominator.clamp(min=self.epsilon)

    def flatten(tensor):
        """Flattens a given tensor such that the channel axis is first.
        The shapes are transformed as follows:
           (N, C, D, H, W) -> (C, N * D * H * W)
        """
        C = tensor.size(1)
        # new axis order
        axis_order = (1, 0) + tuple(range(2, tensor.dim()))
        # Transpose: (N, C, D, H, W) -> (C, N, D, H, W)
        transposed = tensor.permute(axis_order)
        # Flatten: (C, N, D, H, W) -> (C, N * D * H * W)
        return transposed.view(C, -1)

and this is what my training code looks like
for index,(image, mask) in enumerate(train_loader):
            image = torch.unsqueeze(image,0).float().cuda()
            label = mask.cuda()
            # label = label.view(-1,)
            output_1, output_2 = model(image)
            max_output = torch.argmax(output_2, 1)
            loss = loss_function(max_output,label)#max output shape =torch.Size([1, 128, 128, 128]) and labe shape = torch.Size([1, 128, 128, 128])
            print(loss)
            losses.append(loss.item())
            optimizer = optim.Adam(model.parameters())
            optimizer.zero_grad()
            loss.backward()

but when i run this i get
    Traceback (most recent call last):
      File "train.py", line 89, in <module>
        loss.backward()
      File "/home/bubbles/.local/lib/python3.6/site-packages/torch/tensor.py", line 107, in backward
        torch.autograd.backward(self, gradient, retain_graph, create_graph)
      File "/home/bubbles/.local/lib/python3.6/site-packages/torch/autograd/__init__.py", line 93, in backward
        allow_unreachable=True)  # allow_unreachable flag
    RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn

I am not sure how to move forward, any suggestions would be really helpful .
Thanks in advance