From f450325e81056bc209b2d38037c7d105a5efc813 Mon Sep 17 00:00:00 2001
From: Sean <seannaren>
Date: Sat, 2 Apr 2016 16:02:58 +0100
Subject: added base CTCCriterion

---
 CTCCriterion.lua | 85 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 85 insertions(+)
 create mode 100644 CTCCriterion.lua

diff --git a/CTCCriterion.lua b/CTCCriterion.lua
new file mode 100644
index 0000000..1449db0
--- /dev/null
+++ b/CTCCriterion.lua
@@ -0,0 +1,85 @@
+require 'warp_ctc'
+
+local CTCCriterion, parent = torch.class('nn.CTCCriterion', 'nn.Criterion')
+
+function CTCCriterion:__init()
+    parent.__init(self)
+    self.acts = torch.Tensor()
+    self.convertedGradients = torch.Tensor()
+end
+
+function CTCCriterion:updateOutput(output, labels)
+    local tensorSizes = output:size()
+    local acts = self:createCTCBatch(output, tensorSizes)
+    local sizes = {} -- For each batch we state the number of time steps.
+    for x = 1, tensorSizes[1] do
+        table.insert(sizes, tensorSizes[2])
+    end
+    if (output:type() == 'torch.CudaTensor') then
+        local grads = torch.CudaTensor()
+        self.output = sumCosts(gpu_ctc(acts, grads, labels, sizes))
+    else
+        local grads = torch.Tensor()
+        self.output = sumCosts(cpu_ctc(acts:float(), grads:float(), labels, sizes))
+    end
+
+    return self.output
+end
+
+function CTCCriterion:updateGradInput(output, labels)
+    local tensorSizes = output:size()
+    local acts = self:createCTCBatch(output, tensorSizes)
+    local sizes = {}
+    for x = 1, tensorSizes[1] do
+        table.insert(sizes, tensorSizes[2])
+    end
+    local grads = acts:clone():zero()
+    if (output:type() == 'torch.CudaTensor') then
+        gpu_ctc(acts, grads, labels, sizes)
+    else
+        cpu_ctc(acts:float(), grads:float(), labels, sizes)
+    end
+    self.gradInput = self:revertBatching(grads, tensorSizes):typeAs(output)
+    return self.gradInput
+end
+
+--If batching occurs multiple costs are returned. We sum the costs and return.
+function sumCosts(list)
+    local acc
+    for k, v in ipairs(list) do
+        if 1 == k then
+            acc = v
+        else
+            acc = acc + v
+        end
+    end
+    return acc
+end
+
+--[[
+-- Converts the outputs into batch warp-ctc format seen at the end of the README here:
+-- https://github.com/baidu-research/warp-ctc/blob/master/torch_binding/TUTORIAL.md
+ ]]
+function CTCCriterion:createCTCBatch(output, sizes)
+    self.acts:resize(sizes[1] * sizes[2], sizes[3]):zero()
+    local counter = 1
+    for i = 1, sizes[2] do
+        for j = 1, sizes[1] do
+            self.acts[counter] = output[j][i]
+            counter = counter + 1
+        end
+    end
+    return self.acts
+end
+
+function CTCCriterion:revertBatching(gradients, sizes)
+    self.convertedGradients:resize(sizes[1], sizes[2], sizes[3]):zero()
+    local counter = 1
+    for i = 1, sizes[2] do
+        for j = 1, sizes[1] do
+            self.convertedGradients[j][i] = gradients[counter]
+            counter = counter + 1
+        end
+    end
+    return self.convertedGradients
+end
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