times_two_example.lua

require 'nn'

require 'TimesTwo'

local times_two = nn.TimesTwo()

local input = torch.randn(4, 5)
local output = times_two:forward(input)

print('here is input:')
print(input)

print('here is output:')
print(output)

local gradOutput = torch.randn(4, 5)
local gradInput = times_two:backward(input, gradOutput)

print('here is gradOutput:')
print(gradOutput)

print('here is gradInput')
print(gradInput)

TimesTwo.lua

require 'nn'

local times_two, parent = torch.class('nn.TimesTwo', 'nn.Module')


function times_two:__init()
  parent.__init(self)
end


function times_two:updateOutput(input)
  self.output:mul(input, 2)
  return self.output
end


function times_two:updateGradInput(input, gradOutput)
  self.gradInput:mul(gradOutput, 2)
  return self.gradInput
end