Filter padding properly in LabelSmoothedCrossEntropyCriterion (#229)

fairseq/criterions/label_smoothed_cross_entropy.py

@@ -7,7 +7,6 @@
 
 import math
 import torch
-from torch.autograd import Variable
 import torch.nn.functional as F
 
 from fairseq import utils
@@ -15,41 +14,6 @@ from fairseq import utils
 from . import FairseqCriterion, register_criterion
 
 
-class LabelSmoothedNLLLoss(torch.autograd.Function):
-
-    @staticmethod
-    def forward(ctx, input, target, eps, padding_idx, weights, reduce=True):
-        grad_input = input.new(input.size()).zero_()
-        target = target.view(target.size(0), 1)
-        grad_input = grad_input.scatter_(grad_input.dim() - 1, target, eps - 1)
-
-        norm = grad_input.size(-1)
-        if weights is not None:
-            if isinstance(grad_input, Variable) and not isinstance(weights, Variable):
-                weights = Variable(weights, requires_grad=False)
-            norm = weights.sum()
-            grad_input.mul(weights.view(1, weights.size(0)).expand_as(grad_input))
-
-        if padding_idx is not None:
-            norm -= 1 if weights is None else weights[padding_idx]
-            grad_input.select(grad_input.dim() - 1, padding_idx).fill_(0)
-
-        grad_input = grad_input.add(-eps / norm)
-
-        ctx.grad_input = grad_input
-        if reduce:
-            return grad_input.view(-1).dot(input.view(-1))
-        else:
-            return grad_input * input
-
-    @staticmethod
-    def backward(ctx, grad):
-        grad_input = ctx.grad_input
-        if not isinstance(grad_input, torch.autograd.Variable):
-            grad_input = utils.volatile_variable(grad_input)
-        return grad_input * grad, None, None, None, None, None
-
-
 @register_criterion('label_smoothed_cross_entropy')
 class LabelSmoothedCrossEntropyCriterion(FairseqCriterion):
 
@@ -73,10 +37,16 @@ class LabelSmoothedCrossEntropyCriterion(FairseqCriterion):
         """
         net_output = model(**sample['net_input'])
         lprobs = model.get_normalized_probs(net_output, log_probs=True)
-        lprobs = lprobs.view(-1, lprobs.size(-1))
-        target = sample['target'].view(-1)
-        loss = LabelSmoothedNLLLoss.apply(lprobs, target, self.eps, self.padding_idx, None, reduce)
-        nll_loss = F.nll_loss(lprobs, target, size_average=False, ignore_index=self.padding_idx, reduce=reduce)
+        target = sample['target'].unsqueeze(-1)
+        non_pad_mask = target.ne(self.padding_idx)
+        nll_loss = -lprobs.gather(dim=-1, index=target)[non_pad_mask]
+        smooth_loss = -lprobs.sum(dim=-1, keepdim=True)[non_pad_mask]
+        if reduce:
+            nll_loss = nll_loss.sum()
+            smooth_loss = smooth_loss.sum()
+        eps_i = self.eps / lprobs.size(-1)
+        loss = (1. - self.eps) * nll_loss + eps_i * smooth_loss
+
         sample_size = sample['target'].size(0) if self.args.sentence_avg else sample['ntokens']
         logging_output = {
             'loss': utils.item(loss.data) if reduce else loss.data,

tests/test_label_smoothing.py

@@ -4,31 +4,98 @@
 # This source code is licensed under the license found in the LICENSE file in
 # the root directory of this source tree. An additional grant of patent rights
 # can be found in the PATENTS file in the same directory.
-#
 
-import torch
+import argparse
+import copy
 import unittest
-from fairseq.criterions.label_smoothed_cross_entropy import LabelSmoothedNLLLoss
-from torch.autograd import Variable, gradcheck
 
+import torch
+from torch.autograd import Variable
+
+from fairseq import utils
+from fairseq.criterions.cross_entropy import CrossEntropyCriterion
+from fairseq.criterions.label_smoothed_cross_entropy import LabelSmoothedCrossEntropyCriterion
 
-torch.set_default_tensor_type('torch.DoubleTensor')
+import tests.utils as test_utils
 
 
 class TestLabelSmoothing(unittest.TestCase):
 
-    def test_label_smoothing(self):
-        input = Variable(torch.randn(3, 5), requires_grad=True)
-        idx = torch.rand(3) * 4
-        target = Variable(idx.long())
-        criterion = LabelSmoothedNLLLoss()
-        self.assertTrue(gradcheck(
-            lambda x, y: criterion.apply(x, y, 0.1, 2, None), (input, target)
-        ))
-        weights = torch.ones(5)
-        weights[2] = 0
-        self.assertTrue(gradcheck(lambda x, y: criterion.apply(x, y, 0.1, None, weights), (input, target)))
-        self.assertTrue(gradcheck(lambda x, y: criterion.apply(x, y, 0.1, None, None), (input, target)))
+    def setUp(self):
+        # build dictionary
+        self.d = test_utils.dummy_dictionary(3)
+        vocab = len(self.d)
+        self.assertEqual(vocab, 4 + 3)  # 4 special + 3 tokens
+        self.assertEqual(self.d.pad(), 1)
+        self.assertEqual(self.d.eos(), 2)
+        self.assertEqual(self.d.unk(), 3)
+        pad, eos, unk, w1, w2, w3 = 1, 2, 3, 4, 5, 6
+
+        # build dataset
+        self.data = [
+            # the first batch item has padding
+            {'source': torch.LongTensor([w1, eos]), 'target': torch.LongTensor([w1, eos])},
+            {'source': torch.LongTensor([w1, eos]), 'target': torch.LongTensor([w1, w1, eos])},
+        ]
+        self.sample = next(test_utils.dummy_dataloader(self.data))
+
+        # build model
+        self.args = argparse.Namespace()
+        self.args.sentence_avg = False
+        self.args.probs = torch.FloatTensor([
+            #      pad   eos  unk   w1   w2   w3
+            [0.05, 0.05, 0.1, 0.05, 0.3, 0.4, 0.05],
+            [0.05, 0.10, 0.2, 0.05, 0.2, 0.3, 0.10],
+            [0.05, 0.15, 0.3, 0.05, 0.1, 0.2, 0.15],
+        ]).unsqueeze(0).expand(2, 3, 7)  # add batch dimension
+        self.model = test_utils.TestModel.build_model(self.args, self.d, self.d)
+
+    def test_nll_loss(self):
+        self.args.label_smoothing = 0.1
+        nll_crit = CrossEntropyCriterion(self.args, self.d, self.d)
+        smooth_crit = LabelSmoothedCrossEntropyCriterion(self.args, self.d, self.d)
+        nll_loss, nll_sample_size, nll_logging_output = nll_crit(self.model, self.sample)
+        smooth_loss, smooth_sample_size, smooth_logging_output = smooth_crit(self.model, self.sample)
+        self.assertLess(abs(nll_loss - nll_logging_output['loss']), 1e-6)
+        self.assertLess(abs(nll_loss - smooth_logging_output['nll_loss']), 1e-6)
+
+    def test_padding(self):
+        self.args.label_smoothing = 0.1
+        crit = LabelSmoothedCrossEntropyCriterion(self.args, self.d, self.d)
+        loss, _, logging_output = crit(self.model, self.sample)
+
+        def get_one_no_padding(idx):
+            # create a new sample with just a single batch item so that there's
+            # no padding
+            sample1 = next(test_utils.dummy_dataloader([self.data[idx]]))
+            args1 = copy.copy(self.args)
+            args1.probs = args1.probs[idx, :, :].unsqueeze(0)
+            model1 = test_utils.TestModel.build_model(args1, self.d, self.d)
+            loss1, _, _ = crit(model1, sample1)
+            return loss1
+
+        loss1 = get_one_no_padding(0)
+        loss2 = get_one_no_padding(1)
+        self.assertAlmostEqual(loss, loss1 + loss2)
+
+    def test_reduction(self):
+        self.args.label_smoothing = 0.1
+        crit = LabelSmoothedCrossEntropyCriterion(self.args, self.d, self.d)
+        loss, _, logging_output = crit(self.model, self.sample, reduce=True)
+        unreduced_loss, _, _ = crit(self.model, self.sample, reduce=False)
+        self.assertAlmostEqual(loss, unreduced_loss.sum())
+
+    def test_zero_eps(self):
+        self.args.label_smoothing = 0.0
+        nll_crit = CrossEntropyCriterion(self.args, self.d, self.d)
+        smooth_crit = LabelSmoothedCrossEntropyCriterion(self.args, self.d, self.d)
+        nll_loss, nll_sample_size, nll_logging_output = nll_crit(self.model, self.sample)
+        smooth_loss, smooth_sample_size, smooth_logging_output = smooth_crit(self.model, self.sample)
+        self.assertAlmostEqual(nll_loss, smooth_loss)
+
+    def assertAlmostEqual(self, t1, t2):
+        self.assertEqual(t1.size(), t2.size(), "size mismatch")
+        self.assertLess((t1 - t2).abs().max(), 1e-6)
 
 
 if __name__ == '__main__':

tests/utils.py

@@ -92,7 +92,7 @@ class TestEncoder(FairseqEncoder):
 class TestIncrementalDecoder(FairseqIncrementalDecoder):
     def __init__(self, args, dictionary):
         super().__init__(dictionary)
-        assert hasattr(args, 'beam_probs')
+        assert hasattr(args, 'beam_probs') or hasattr(args, 'probs')
         args.max_decoder_positions = getattr(args, 'max_decoder_positions', 100)
         self.args = args
 
@@ -116,6 +116,11 @@ class TestIncrementalDecoder(FairseqIncrementalDecoder):
             steps = list(range(tgt_len))
 
         # define output in terms of raw probs
+        if hasattr(self.args, 'probs'):
+            assert self.args.probs.dim() == 3, \
+                'expected probs to have size bsz*steps*vocab'
+            probs = self.args.probs.index_select(1, torch.LongTensor(steps))
+        else:
             probs = torch.FloatTensor(bbsz, len(steps), vocab).zero_()
             for i, step in enumerate(steps):
                 # args.beam_probs gives the probability for every vocab element,