# Diagonal Hessian wrt parameters when using mini-batches

I am interested in computing the diagonal values of the Hessian of the loss function with respect to the parameters of an `nn.Module` to use for statistical inference (standard errors depend on the Hessian). The complication is that the model is estimated using mini-batches, because the full data doesn’t fit into memory, and existing solutions I’ve come across only give you the Hessian for the loss evaluated on a single batch of data.

Does anyone have ideas for how to compute the Hessian evaluated on the full dataset? For a single batch, a (not safe) method like the code below works. My current thinking is that I can just compute the Hessian for a loss function with `sum’ reduction on each batch separately and then sum across all batches, but I haven’t yet convinced myself this is valid so figured I’d see if someone else had thoughts

``````_input=torch.randn(32,3)
layer = nn.Linear(3,4)
criterion=nn.CrossEntropyLoss()

weight = layer.weight

def func(weight):
del layer.weight
layer.weight=weight
return criterion(layer(_input), torch.zeros(len(_input),dtype=torch.long))

``````