def physics_loss(pinn_output, mass, forces):

# Create a tensor of time values

time = torch.linspace(0, (len(pinn_output)-1)*0.01, len(pinn_output)).requires_grad_(True)

```
# Repeat the time tensor to match the dimensions of pinn_output
time = time.unsqueeze(1).repeat(1, pinn_output.shape[1])
# Compute velocity by differentiating position with respect to time
v_pred = torch.autograd.grad(pinn_output, time, grad_outputs=torch.ones_like(pinn_output), create_graph=True, allow_unused=True)[0]
# Compute acceleration by differentiating velocity with respect to time
a_pred = torch.autograd.grad(v_pred, time, grad_outputs=torch.ones_like(v_pred), create_graph=True, allow_unused=True)[0]
# Adjust for gravity in the y-direction
a_pred[:, 1] -= 9.81 # Subtract gravity from y-acceleration
# Compute the physics loss
return torch.mean((forces - mass * a_pred) ** 2)
```

I have this physics loss equation and I am trying to get v_pred and a_pred but I constantly get errors like “TypeError: ones_like(): argument ‘input’ (position 1) must be Tensor, not NoneType”