#!/usr/bin/env luajit

--[[

   Copyright (c) 2016 Idiap Research Institute, http://www.idiap.ch/
   Written by Francois Fleuret <francois.fleuret@idiap.ch>

   This file is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License version 3 as
   published by the Free Software Foundation.

   It is distributed in the hope that it will be useful, but WITHOUT
   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
   License for more details.

   You should have received a copy of the GNU General Public License
   along with this file.  If not, see <http://www.gnu.org/licenses/>.

]]--

require 'torch'
require 'nn'
require 'dagnn'

torch.setdefaulttensortype('torch.DoubleTensor')
torch.manualSeed(1)

function checkGrad(model, criterion, input, target)
   local params, gradParams = model:getParameters()

   local epsilon = 1e-5

   local output = model:forward(input)
   local loss = criterion:forward(output, target)
   local gradOutput = criterion:backward(output, target)
   gradParams:zero()
   model:backward(input, gradOutput)
   local analyticalGradParam = gradParams:clone()

   local err = 0

   for i = 1, params:size(1) do
      local x = params[i]

      params[i] = x - epsilon
      local output0 = model:forward(input)
      local loss0 = criterion:forward(output0, target)

      params[i] = x + epsilon
      local output1 = model:forward(input)
      local loss1 = criterion:forward(output1, target)

      params[i] = x

      local ana = analyticalGradParam[i]
      local num = (loss1 - loss0) / (2 * epsilon)

      if num ~= ana then
         err = math.max(err, torch.abs(num - ana) / torch.abs(num))
      end
   end

   return err
end

function printTensorTable(t)
   if torch.type(t) == 'table' then
      for i, t in pairs(t) do
         print('-- ELEMENT [' .. i .. '] --')
         printTensorTable(t)
      end
   else
      print(tostring(t))
   end
end

--               +-- Linear(10, 10) --> ReLU --> d --+
--              /                              /      \
--             /                              /        \
--  --> a --> b -----------> c --------------+          e -->
--                            \                        /
--                             \                      /
--                              +----- Mul(-1) ------+

model = nn.DAG()

a = nn.Linear(50, 10)
b = nn.ReLU()
c = nn.Linear(10, 15)
d = nn.CMulTable()
e = nn.CAddTable()

model:connect(a, b, c)
model:connect(b, nn.Linear(10, 15), nn.ReLU(), d)
model:connect(d, e)
model:connect(c, d)
model:connect(c, nn.Mul(-1), e)

model:setInput(a)
model:setOutput(e)

local input = torch.Tensor(30, 50):uniform()
local output = model:updateOutput(input):clone()

output:uniform()

print('Error = ' .. checkGrad(model, nn.MSECriterion(), input, output))

print('Writing /tmp/graph.dot')
model:saveDot('/tmp/graph.dot')