Hello guys, I am new to this PyTorch environment

Here, I鈥檓 trying to construct a new loss balancing technique for my Forward problem with PINNs using *NVIDIA-modulus*- nvidia / Modulus / Modulus 路 GitLab.

I would like to alter the **losses during training step=0**. For e.g., I would like to initialize **each losses[key]=1 for step=0**

```
class Aggregator(nn.Module):
"""
Base class for loss aggregators
"""
def __init__(self, params, num_losses, weights):
super().__init__()
self.params: List[torch.Tensor] = list(params)
self.num_losses: int = num_losses
self.weights: Optional[Dict[str, float]] = weights
self.device: torch.device
self.device = list(set(p.device for p in self.params))[0]
self.init_loss: torch.Tensor = torch.tensor(0.0, device=self.device)
def weigh_losses_initialize(
weights: Optional[Dict[str, float]]
) -> Callable[
[Dict[str, torch.Tensor], Optional[Dict[str, float]]],
Dict[str, torch.Tensor],
]:
if weights is None:
def weigh_losses(
losses: Dict[str, torch.Tensor], weights: None
) -> Dict[str, torch.Tensor]:
return losses
else:
def weigh_losses(
losses: Dict[str, torch.Tensor], weights: Dict[str, float]
) -> Dict[str, torch.Tensor]:
for key in losses.keys():
if key not in weights.keys():
weights.update({key: 1.0})
losses = {key: weights[key] * losses[key] for key in losses.keys()}
return losses
return weigh_losses
self.weigh_losses = weigh_losses_initialize(self.weights)
class SoftAdapt(Aggregator):
"""
SoftAdapt for loss aggregation
Reference: "Heydari, A.A., Thompson, C.A. and Mehmood, A., 2019.
Softadapt: Techniques for adaptive loss weighting of neural networks with multi-part loss functions.
arXiv preprint arXiv: 1912.12355."
"""
def __init__(self, params, num_losses, eps=1e-8, weights=None):
super().__init__(params, num_losses, weights)
self.eps: float = eps
self.register_buffer(
"prev_losses", torch.zeros(self.num_losses, device=self.device)
)
self.register_buffer(
"lmbda_ema", torch.ones(self.num_losses, device=self.device)
)
def forward(self, losses: Dict[str, torch.Tensor], step: int) -> torch.Tensor:
"""
Weights and aggregates the losses using the original variant of the softadapt algorithm
Parameters
----------
losses : Dict[str, torch.Tensor]
A dictionary of losses.
step : int
Optimizer step.
Returns
-------
loss : torch.Tensor
Aggregated loss.
"""
# weigh losses
losses = self.weigh_losses(losses, self.weights)
# Initialize loss
loss: torch.Tensor = torch.zeros_like(self.init_loss)
# Aggregate losses by summation at step 0
if step == 0:
for i, key in enumerate(losses.keys()):
self.lmbda_ema[i] = 1/(losses[key]+ self.eps)
losses[key] = losses[key]* self.lmbda_ema[i]
loss += losses[key].clone().detach() # simply, initial losses[key] = 1
# Aggregate losses using SoftAdapt for step > 0
else:
lmbda: torch.Tensor = torch.ones_like(self.prev_losses)
lmbda_sum: torch.Tensor = torch.zeros_like(self.prev_loss)
losses_stacked: torch.Tensor = torch.stack(list(losses.values()))
normalizer: torch.Tensor = (losses_stacked / self.prev_losses).max()
for i, key in enumerate(losses.keys()):
with torch.no_grad():
lmbda[i] = torch.exp(
losses[key] / (self.prev_losses[i] + self.eps) - normalizer
)
lmbda_sum += lmbda[i]
loss += lmbda[i].clone() * losses[key]
self.prev_losses[i] = losses[key].clone().detach()
loss *= self.num_losses / (lmbda_sum + self.eps)
return loss
```

The error:

```
File "/opt/conda/lib/python3.8/site-packages/functorch/_src/monkey_patching.py", line 77, in _backward return _old_backward(*args, **kwargs)
File "/opt/conda/lib/python3.8/site-packages/torch/_tensor.py", line 402, in backward
torch.autograd.backward(self, gradient, retain_graph, create_graph, inputs=inputs)
File "/opt/conda/lib/python3.8/site-packages/torch/autograd/__init__.py", line 191, in backward
Variable._execution_engine.run_backward( # Calls into the C++ engine to run the backward pass
RuntimeError: element 0 of tensors does not require grad and does not have a grad_fn
```

Thanks in advance