add Scheduled Sampling at training

Readme.md

@@ -1,6 +1,6 @@
 
 # char-rnn-chinese
-Based on https://github.com/karpathy/char-rnn. make the code work well with Chinese.
+Based on Andrej Karpathy's code https://github.com/karpathy/char-rnn and Samy Bengio's paper http://arxiv.org/abs/1506.03099 
 
 ## Chinese process
 Make the code can process both English and Chinese characters.
@@ -10,6 +10,20 @@ This is my first touch of Lua, so the string process seems silly, but it works w
 I also add an option called 'min_freq' because the vocab size in Chinese is very big, which makes the parameter num increase a lot.
 So delete some rare character may help.
 
+## Scheduled Sampling
+Samy Bengio's paper [Scheduled Sampling for Sequence Prediction with Recurrent Neural Networks](http://arxiv.org/abs/1506.03099) in NIPS15
+propose a simple but power method to implove RNN.
+In my experiment, I find it helps a lot to avoid overfitting and make the test loss go deeper. I only use linear decay.
+Use `-use_ss` to turn on or turn off scheduled sampling, default is on. `-start_ss` is the start aomunt of real data, I suggest to use 1 because our model should learn data without noise at the very begining. `-min_ss` is also very important as too much noise will hurt performance. Finally, `-decay_ss` is the linear decay rate.
+
+
+## Model conversion between cpu and gpu
+I add a script to convert a model file trained by gpu to cpu model.
+You can try it as follow:
+```bash
+$ th convert.lua gpu_model cpu_model
+```
+
 ## web interface
 A web demo is added for others to test model easily, based on sub/pub of redis.
 I use redis because i can't found some good RPC or WebServer work well integrated with Torch.
@@ -35,12 +49,6 @@ $ nohup th web_backend.lua &
 $ nohup python web_server.py & 
 ```
 
-## Model conversion between cpu and gpu
-I add a script to convert a model file trained by gpu to cpu model.
-You can try it as follow:
-```bash
-$ th convert.lua gpu_model cpu_model
-```
 
 -----------------------------------------------
 ## Karpathy's raw Readme

train.lua

@@ -60,11 +60,17 @@ cmd:option('-savefile','lstm','filename to autosave the checkpont to. Will be in
 -- GPU/CPU
 cmd:option('-gpuid',0,'which gpu to use. -1 = use CPU')
 cmd:option('-opencl',0,'use OpenCL (instead of CUDA)')
+-- Scheduled Sampling
+cmd:option('-use_ss', 1, 'whether use scheduled sampling during training')
+cmd:option('-start_ss', 1, 'start amount of truth to be github to the model when using ss')
+cmd:option('-decay_ss', 0.01666, 'ss amount decay rate of each epoch')
+cmd:option('-min_ss', 0.5, 'minimum amount of truth to be given to the model when using ss')
 cmd:text()
 
 -- parse input params
 opt = cmd:parse(arg)
 torch.manualSeed(opt.seed)
+math.randomseed(opt.seed)
 -- train / val / test split for data, in fractions
 local test_frac = math.max(0, 1 - (opt.train_frac + opt.val_frac))
 local split_sizes = {opt.train_frac, opt.val_frac, test_frac} 
@@ -238,7 +244,15 @@ function feval(x)
     local loss = 0
     for t=1,opt.seq_length do
         clones.rnn[t]:training() -- make sure we are in correct mode (this is cheap, sets flag)
-        local lst = clones.rnn[t]:forward{x[{{}, t}], unpack(rnn_state[t-1])}
+        -- flip a coin to decide weather use scheduled sampling
+        if opt.use_ss == 1 and t > 1 and math.random() > ss_current then
+            local probs = torch.exp(predictions[t-1]):squeeze()
+            _,samples = torch.max(probs,2)
+            xx = samples:view(samples:nElement())
+        else
+            xx = x[{{}, t}]
+        end
+        local lst = clones.rnn[t]:forward{xx, unpack(rnn_state[t-1])}
         rnn_state[t] = {}
         for i=1,#init_state do table.insert(rnn_state[t], lst[i]) end -- extract the state, without output
         predictions[t] = lst[#lst] -- last element is the prediction
@@ -277,6 +291,7 @@ local optim_state = {learningRate = opt.learning_rate, alpha = opt.decay_rate}
 local iterations = opt.max_epochs * loader.ntrain
 local iterations_per_epoch = loader.ntrain
 local loss0 = nil
+ss_current = opt.start_ss
 for i = 1, iterations do
     local epoch = i / loader.ntrain
 
@@ -296,6 +311,12 @@ for i = 1, iterations do
         end
     end
 
+    -- decay schedule sampling amount
+    if opt.use_ss == 1 and i % loader.ntrain == 0 and ss_current > opt.min_ss then
+        ss_current = opt.start_ss - opt.decay_ss * epoch
+        print('decay schedule sampling amount to ' .. ss_current)
+    end
+
     -- every now and then or on last iteration
     if i % opt.eval_val_every == 0 or i == iterations then
         -- evaluate loss on validation data