MulConstant.lua

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

function MulConstant:__init(constant_scalar,ip)
  parent.__init(self)
  assert(type(constant_scalar) == 'number', 'input is not scalar!')
  self.constant_scalar = constant_scalar
    
  -- default for inplace is false
   self.inplace = ip or false
   if (ip and type(ip) ~= 'boolean') then
      error('in-place flag must be boolean')
   end
end

function MulConstant:updateOutput(input)
  if self.inplace then
    input:mul(self.constant_scalar)
    self.output = input
  else
    self.output:resizeAs(input)
    self.output:copy(input)
    self.output:mul(self.constant_scalar)
  end
  return self.output
end 

function MulConstant:updateGradInput(input, gradOutput)
  if self.inplace then
    gradOutput:mul(self.constant_scalar)
    self.gradInput = gradOutput
    -- restore previous input value
    input:div(self.constant_scalar)
  else
    self.gradInput:resizeAs(gradOutput)
    self.gradInput:copy(gradOutput)
    self.gradInput:mul(self.constant_scalar)
  end
  return self.gradInput
end