Refine code and comments

1. Remove checking for num_neg_samples.
2. Fix dims of Output(Cost) and Input(Bias).
3. Renamed num_sampled_classes to num_neg_samples.
4. Add TODO for add more distribution sampler.
5. Init grad_data of bias by zero.
6. Refine comments.
7. Register a kernel for type double.

paddle/operators/nce_op.cc

 /* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
 
-   Licensed under the Apache License, Version 2.0 (the "License");
-   you may not use this file except in compliance with the License.
-   You may obtain a copy of the License at
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
 
-   http://www.apache.org/licenses/LICENSE-2.0
+    http://www.apache.org/licenses/LICENSE-2.0
 
-   Unless required by applicable law or agreed to in writing, software
-   distributed under the License is distributed on an "AS IS" BASIS,
-   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-   See the License for the specific language governing permissions and
-   limitations under the License. */
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License. */
 
 #include "paddle/operators/nce_op.h"
 
@@ -39,25 +39,25 @@ class NCEOp : public framework::OperatorWithKernel {
       PADDLE_ENFORCE_EQ(ctx->GetInputDim("Weight")[0],
                         ctx->GetInputDim("Bias")[0]);
     }
-    auto num_sampled_classes = ctx->Attrs().Get<int>("num_sampled_classes");
-    auto num_classes = ctx->Attrs().Get<int>("num_classes");
+    auto num_neg_samples = ctx->Attrs().Get<int>("num_neg_samples");
+    auto num_total_classes = ctx->Attrs().Get<int>("num_total_classes");
     std::vector<int> sampled_labels =
         ctx->Attrs().Get<std::vector<int>>("sampled_labels");
-    PADDLE_ENFORCE_EQ(num_classes, ctx->GetInputDim("Weight")[0]);
-    PADDLE_ENFORCE_LT(num_sampled_classes, num_classes);
+    PADDLE_ENFORCE_EQ(num_total_classes, ctx->GetInputDim("Weight")[0]);
     if (sampled_labels.size() > 0) {
       PADDLE_ENFORCE_EQ(sampled_labels.size(),
-                        static_cast<size_t>(num_sampled_classes));
+                        static_cast<size_t>(num_neg_samples));
     }
     // set dims of output(Out)
     std::vector<int64_t> out_dims;
     out_dims.push_back(x_dims[0]);
+    out_dims.push_back(1);
     ctx->SetOutputDim("Cost", framework::make_ddim(out_dims));
 
     // set dims of output(SampleOut)
     std::vector<int64_t> sample_out_dims;
     sample_out_dims.push_back(x_dims[0]);
-    sample_out_dims.push_back(num_sampled_classes + num_true_classes);
+    sample_out_dims.push_back(num_neg_samples + num_true_classes);
     ctx->SetOutputDim("SampleLogits", framework::make_ddim(sample_out_dims));
     ctx->SetOutputDim("SampleLabels", framework::make_ddim(sample_out_dims));
   }
@@ -76,34 +76,59 @@ class NCEOpMaker : public framework::OpProtoAndCheckerMaker {
   NCEOpMaker(framework::OpProto* proto, framework::OpAttrChecker* op_checker)
       : OpProtoAndCheckerMaker(proto, op_checker) {
     AddInput("Input", "(Tensor) A tensor of shape [batch_size, dim].");
-    AddInput("Label",
-             "(Tensor) A tensor of shape [batch_size, num_true_class]. "
-             "'num_true_class' is the number of target class in each sample.");
+    AddInput(
+        "Label",
+        "(Tensor) A tensor of shape [batch_size, num_true_class]. "
+        "'num_true_class' is the number of target classes in each sample."
+        "The number of target classes per sample should be same. "
+        "If you have a variable number of target classes, "
+        "you can pad them out to a constant number by either repeating them"
+        " or by padding with an otherwise unused class.)");
     AddInput("Weight",
              "(Tensor) A tensor of shape [num_class, dim]. 'num_class' is the "
              "total number of class.");
-    AddInput("Bias",
-             "(Tensor) A tensor of shape [num_class]. 'num_class' is the total "
-             "number of class. It is a dispensable input.")
+    AddInput(
+        "Bias",
+        "(Tensor) A tensor of shape [num_class, 1]. 'num_class' is the total "
+        "number of class. It is a dispensable input.")
         .AsDispensable();
     AddInput("SampleWeight",
-             "(Tensor) A tensor of shape [batch_size] storing a weight for "
+             "(Tensor) A tensor of shape [batch_size, 1] storing a weight for "
              "each sample. And it is a dispensable input. The default value of "
              "sample is 1.")
         .AsDispensable();
     AddOutput("Cost",
-              "(Tensor) A tensor of shape [batch_size]. Cost of samples.");
-    AddOutput("SampleLogits", "An intermediate tensor.").AsIntermediate();
-    AddOutput("SampleLabels", "An intermediate tensor.").AsIntermediate();
-    AddAttr<int>("num_classes", "Total number of classes.");
-    AddAttr<int>("num_sampled_classes", "The number of negative classes.")
+              "(Tensor) A tensor of shape [batch_size, 1]. Cost of samples.");
+    AddOutput("SampleLogits",
+              "An intermediate tensor of shape[batch_size, num_neg_samples + "
+              "num_pos_samples]."
+              "This tensor is output of forward kernel and used in backward "
+              "kernel to compute grads."
+              "Given X is  the dot product of input tensor and sampled labels' "
+              "weights."
+              "Then 'SampleLogits' is sigmoid(X).")
+        .AsIntermediate();
+    AddOutput("SampleLabels",
+              "An intermediate tensor of shape[batch_size, num_neg_samples + "
+              "num_pos_samples]."
+              "This tensor is output of forward kernel and used in backward "
+              "kernel to compute grads."
+              "")
+        .AsIntermediate();
+    AddAttr<int>("num_total_classes",
+                 "Total number of classes in all samples.");
+    AddAttr<int>("num_neg_samples",
+                 "The number of negative classes. The default value is 10.")
         .SetDefault(10);
-    AddAttr<std::vector<int>>("sampled_labels", "");
+    AddAttr<std::vector<int>>("custom_neg_classes",
+                              "This attribute only be used in unitest. Classes "
+                              "in this list wiil be used as negative classes "
+                              "for every samples. Under normal conditions, "
+                              "user should avoid setting this attribute.");
     AddComment(R"DOC(
-Computes and returns the noise-contrastive estimation training loss.
+Compute and return the noise-contrastive estimation training loss.
 See [Noise-contrastive estimation: A new estimation principle for unnormalized statistical models](http://www.jmlr.org/proceedings/papers/v9/gutmann10a/gutmann10a.pdf).
-By default this uses a uniform distribution for sampling.
-The number of target classes per example should be same. If you have a variable number of target classes, you can pad them out to a constant number by either repeating them or by padding with an otherwise unused class.
+By default this operator uses a uniform distribution for sampling.
 )DOC");
   }
 };
@@ -119,7 +144,7 @@ class NCEOpGrad : public framework::OperatorWithKernel {
     PADDLE_ENFORCE(ctx->HasInput("SampleLogits"));
     PADDLE_ENFORCE(ctx->HasInput("SampleLabels"));
     PADDLE_ENFORCE(ctx->HasInput(framework::GradVarName("Cost")),
-                   "The input(Out@GRAD) should not be null");
+                   "The input(Out@GRAD) should not be null.");
 
     auto x_dims = ctx->GetInputDim("Input");
     auto x_grad_name = framework::GradVarName("Input");
@@ -154,6 +179,8 @@ class NCEOpGrad : public framework::OperatorWithKernel {
 
 namespace ops = paddle::operators;
 REGISTER_OP(nce, ops::NCEOp, ops::NCEOpMaker, nce_grad, ops::NCEOpGrad);
-REGISTER_OP_CPU_KERNEL(nce, ops::NCEKernel<paddle::platform::CPUPlace, float>);
+REGISTER_OP_CPU_KERNEL(nce, ops::NCEKernel<paddle::platform::CPUPlace, float>,
+                       ops::NCEKernel<paddle::platform::CPUPlace, double>);
 REGISTER_OP_CPU_KERNEL(nce_grad,
-                       ops::NCEGradKernel<paddle::platform::CPUPlace, float>);
+                       ops::NCEGradKernel<paddle::platform::CPUPlace, float>,
+                       ops::NCEGradKernel<paddle::platform::CPUPlace, double>);

paddle/operators/nce_op.h

@@ -22,7 +22,7 @@
 namespace paddle {
 namespace operators {
 
-using Tensor = framework::Tensor;
+using framework::Tensor;
 
 template <typename T, int MajorType = Eigen::RowMajor,
           typename IndexType = Eigen::DenseIndex>
@@ -35,8 +35,8 @@ void PrepareSamples(const framework::ExecutionContext& context) {
   auto label_dims = label->dims();
   int num_classes = context.Attr<int>("num_classes");
   // for unitest
-  std::vector<int> sampled_labels =
-      context.Attr<std::vector<int>>("sampled_labels");
+  std::vector<int> custom_neg_classes =
+      context.Attr<std::vector<int>>("custom_neg_classes");
   // random machine
   std::random_device rd;
   std::mt19937 rng(rd());
@@ -54,12 +54,13 @@ void PrepareSamples(const framework::ExecutionContext& context) {
     for (; j < num_label; ++j) {
       sample_labels_data[index++] = label_data[i * num_label + j];
     }
-    if (sampled_labels.size() > 0) {
-      for (auto label : sampled_labels) {
+    if (custom_neg_classes.size() > 0) {
+      for (auto label : custom_neg_classes) {
         sample_labels_data[index++] = label;
       }
     } else {
       for (; j < sample_labels_dims[1]; ++j) {
+        // TODO: support more distribution sampling
         sample_labels_data[index++] = rand(rng);
       }
     }
@@ -176,6 +177,7 @@ class NCEGradKernel : public framework::OpKernel<T> {
     auto d_bias = context.Output<Tensor>(framework::GradVarName("Bias"));
     if (d_bias != nullptr) {
       T* d_bias_data = d_bias->mutable_data<T>(context.GetPlace());
+      std::fill(d_bias_data, d_bias_data + d_bias->numel(), 0.0);
       for (size_t i = 0; i < sample_labels->numel(); ++i) {
         d_bias_data[sample_labels_data[i]] += sample_grad_data[i];
       }
@@ -183,7 +185,8 @@ class NCEGradKernel : public framework::OpKernel<T> {
     // get d_w
     auto d_w = context.Output<Tensor>(framework::GradVarName("Weight"));
     if (d_w != nullptr) {
-      d_w->mutable_data<T>(context.GetPlace());
+      auto d_w_data = d_w->mutable_data<T>(context.GetPlace());
+      std::fill(d_w_data, d_w_data + d_w->numel(), 0.0);
       auto d_w_matrix = EigenMatrix<T>::From(*d_w);
       auto x_matrix = EigenMatrix<T>::From(*(context.Input<Tensor>("Input")));
       for (size_t i = 0; i < sample_labels->numel(); ++i) {

python/paddle/v2/fluid/tests/test_nce.py

@@ -18,25 +18,25 @@ def nce(input, weight, bias, sample_weight, labels, num_classes,
             samples.append((i, num, False, w))
             sample_labels.append(num)
     # forward bias
-    sampleOut = np.zeros(len(samples)).astype(np.float32)
+    sample_out = np.zeros(len(samples)).astype(np.float32)
     if bias is not None:
         for i in range(len(samples)):
-            sampleOut[i] = bias[samples[i][1]]
+            sample_out[i] = bias[samples[i][1]]
     # forward weight
     for i in range(len(samples)):
-        sampleOut[i] += np.dot(input[samples[i][0]], weight[samples[i][1]])
+        sample_out[i] += np.dot(input[samples[i][0]], weight[samples[i][1]])
 
     # forward activation
-    sampleOut = 1.0 / (1.0 + np.exp(-sampleOut))
+    sample_out = 1.0 / (1.0 + np.exp(-sample_out))
     # forward cost
     out = np.zeros(batch_size).astype(np.float32)
     b = 1.0 / num_classes * num_sample_class
     for i in range(len(samples)):
-        o = sampleOut[i]
+        o = sample_out[i]
         cost = -np.log(o / (o + b)) if samples[i][2] else -np.log(b / (o + b))
         out[samples[i][0]] += cost * samples[i][3]
-    return (out, np.array(sampleOut).reshape(batch_size,
-                                             num_sample_class + num_true_class),
+    return (out, np.array(sample_out).reshape(
+        batch_size, num_sample_class + num_true_class),
             np.array(sample_labels).reshape(batch_size,
                                             num_sample_class + num_true_class))