class nn.DistanceRatioCriterion has been already assigned a parent class

[Shahnawaz Grewal]

I am a newbie to torch and implementing a work from "Deep Learning Metric Using Triplet Network".  However I am not able to compile the code. I got the following error. 

class nn.DistanceRatioCriterion has been already assigned a parent class

stack traceback:

[C]: in function 'error'

/home/super/torch/install/share/lua/5.1/trepl/init.lua:389: in function 'require'

Main.lua:8: in main chunk

[C]: in function 'dofile'

...uper/torch/install/lib/luarocks/rocks/trepl/scm-1/bin/th:150: in main chunk

[C]: at 0x00405d50

Can someone help me to resolve this error.  

[Tasty Minerals]

Remove "nn" from "nn.DistanceRatioCriterion"

local mycustomClass, parent = torch.class('DistanceRatioCriterion', 'nn.someParentClass')

[Francesco App]

Thank you so much Tasty Minerals. After this error, others appeared running TripletNet code from elad. I have an error even in the forward pass (incorrect number of input). I tried to fix things like this:

optimizer file, function Optimizer:optimize(x,yt)

    local y1 = y[{{},{1}}]

    local y2 = y[{{},{2}}]

    local ytable = {y1,y2}

    local dE_dy = self.Loss:backward(ytable)

    self.Model:backward(x, {dE_dy[1][1],dE_dy[1][2]})

but without success. Is anyone able to run TripletNet code on a Sept-2017 torch7 environment? I've tried with cifar10 and cifar100 db. 

Thank you in advance

Francesco