attempt to call field 'sigmoid' (a nil value)

[SeekPoint]

andy1028@andy1028-Envy:/media/andy1028/data1t/os_prj/github/dl-attention$ th rnn.lua
function: 0x4100c948
vocabulary size: 12
number of parameters in the model: 17420

Training Epoch #1
/home/andy1028/torch/install/bin/luajit: ...e/andy1028/torch/install/share/lua/5.1/autograd/util.lua:97: attempt to call field 'sigmoid' (a nil value)
stack traceback:
...e/andy1028/torch/install/share/lua/5.1/autograd/util.lua:97: in function 'sigmoid'
...ll/share/lua/5.1/autograd/model/RecurrentLSTMNetwork.lua:97: in function 'lstm1'
rnn.lua:55: in function 'fn'
...install/share/lua/5.1/autograd/runtime/codegen/Graph.lua:353: in function 'protectedFn'
...install/share/lua/5.1/autograd/runtime/codegen/Graph.lua:383: in function 'record'
.../install/share/lua/5.1/autograd/runtime/codegen/init.lua:44: in function 'generateFn'
.../install/share/lua/5.1/autograd/runtime/codegen/init.lua:140: in function 'df'
rnn.lua:137: in main chunk
[C]: in function 'dofile'
...1028/torch/install/lib/luarocks/rocks/trepl/scm-1/bin/th:145: in main chunk
[C]: at 0x00405ea0
andy1028@andy1028-Envy:/media/andy1028/data1t/os_prj/github/dl-attention$
andy1028@andy1028-Envy:/media/andy1028/data1t/os_prj/github/dl-attention$