minus '-' syntax not working

[Daniele Molinari]

Trying to execute the example with the '-' syntax presented in https://github.com/torch/nngraph#more-fun-with-graphs results in:
nn.Identity has no negation operator

Replacing input = - nn.Identity() with input = nn.Identity()() then leads to:
both nngraph.Node and nn.Linear have no substraction operator

[Soumith Chintala]

did you update your nngraph package?
luarocks install nngraph

[Daniele Molinari]

Apparently I had an older version.
Thank you very much.