diff --git a/nn.lua b/nn.lua
index 3b5f94f..652f4c1 100644
--- a/nn.lua
+++ b/nn.lua
@@ -59,6 +59,12 @@ local function zeros(n, out)
     return out
 end
 
+local function arange(n, out)
+    out = out or {}
+    for i = 1, n do out[i] = i - 1 end
+    return out
+end
+
 local function allocate(t, out, init)
     out = out or {}
     local size = t
@@ -353,6 +359,10 @@ function Softmax:forward(X)
     return Y
 end
 
+--function Softmax:backward(dY)
+    --return (dY - np.sum(dY * self.sm, axis=-1, keepdims=True)) * self.cache
+--end
+
 function Model:init(nodes_in, nodes_out)
     assert(#nodes_in > 0, #nodes_in)
     assert(#nodes_out > 0, #nodes_out)
@@ -393,6 +403,14 @@ function Model:forward(inputs)
     return outputs
 end
 
+function Model:cleargrad()
+    error("TODO") -- TODO
+end
+
+function Model:print()
+    error("TODO") -- TODO
+end
+
 function Model:collect()
     -- return a flat array of all the weights in the graph.
     -- if Lua had slices, we wouldn't need this. future library idea?
@@ -468,6 +486,7 @@ return {
     prod = prod,
     normal = normal,
     zeros = zeros,
+    arange = arange,
     allocate = allocate,
     init_zeros = init_zeros,
     init_he_uniform = init_he_uniform,