Hi Bhargava!
Without seeing you code, I’m only guessing.  However …



 Bhargava:

In PyTorch nn.NLLLoss() function, when we apply it directly to calculate loss value wrt input and Target value, we get a error mentioning “bool value of Tensor with more than one value is ambiguous”.


NLLLoss is a class, instances of which are callable function objects.
(nll_loss is a function.)
My guess is that you are calling the constructor of NLLLoss with your
input and Target tensors.  The second argument, size_average to
NLLLoss's constructor is a bool, hence your error.
nn.NLLLoss (input, Target)   # bad -- calling constructor incorrectly
nn.NLLLoss() (input, Target)   # good -- calling a default-constructed function object correctly
nn.functional.nll_loss (input, Target)   # good -- calling ordinary function

Good luck!
K. Frank