[src] nnet1: fixing issue in multi-task training (kaldi-asr#1491)

src/nnet/nnet-loss.cc

@@ -367,17 +367,41 @@ void MultiTaskLoss::Eval(const VectorBase<BaseFloat> &frame_weights,
   // allocate diff matrix,
   diff->Resize(num_frames, num_output);
 
+  /// One vector of frame_weights per loss-function,
+  /// The original frame weights are multiplied with
+  /// a mask of `defined targets' according to the 'Posterior'.
+  std::vector<Vector<BaseFloat> > frmwei_have_tgt;
+  for (int32 l = 0; l < loss_vec_.size(); l++) {
+    // copy original weights,
+    frmwei_have_tgt.push_back(Vector<BaseFloat>(frame_weights));
+    // We need to mask-out the frames for which the 'posterior' is not defined (= is empty):
+    int32 loss_beg = loss_dim_offset_[l];   // first column of loss target,
+    int32 loss_end = loss_dim_offset_[l+1]; // (last+1) column of loss target,
+    for (int32 f = 0; f < num_frames; f++) {
+      bool tgt_defined = false;
+      for (int32 p = 0; p < post[f].size(); p++) {
+        if (post[f][p].first >= loss_beg && post[f][p].first < loss_end) {
+          tgt_defined = true;
+          break;
+        }
+      }
+      if (!tgt_defined) {
+        frmwei_have_tgt[l](f) = 0.0; // set zero_weight for the frame with no targets!
+      }
+    }
+  }
+
   // call the vector of loss functions,
   CuMatrix<BaseFloat> diff_aux;
-  for (int32 i = 0; i < loss_vec_.size(); i++) {
-    loss_vec_[i]->Eval(frame_weights,
-      net_out.ColRange(loss_dim_offset_[i], loss_dim_[i]),
-      tgt_mat_.ColRange(loss_dim_offset_[i], loss_dim_[i]),
+  for (int32 l = 0; l < loss_vec_.size(); l++) {
+    loss_vec_[l]->Eval(frmwei_have_tgt[l],
+      net_out.ColRange(loss_dim_offset_[l], loss_dim_[l]),
+      tgt_mat_.ColRange(loss_dim_offset_[l], loss_dim_[l]),
       &diff_aux);
     // Scale the gradients,
-    diff_aux.Scale(loss_weights_[i]);
+    diff_aux.Scale(loss_weights_[l]);
     // Copy to diff,
-    diff->ColRange(loss_dim_offset_[i], loss_dim_[i]).CopyFromMat(diff_aux);
+    diff->ColRange(loss_dim_offset_[l], loss_dim_[l]).CopyFromMat(diff_aux);
   }
 }
 

src/nnet/nnet-loss.h

@@ -90,6 +90,7 @@ class Xent : public LossItf {
 
   /// Get loss value (frame average),
   BaseFloat AvgLoss() {
+    if (frames_.Sum() == 0) return 0.0;
     return (xentropy_.Sum() - entropy_.Sum()) / frames_.Sum();
   }
 
@@ -151,6 +152,7 @@ class Mse : public LossItf {
 
   /// Get loss value (frame average),
   BaseFloat AvgLoss() {
+    if (frames_ == 0) return 0.0;
     return loss_ / frames_;
   }