3

I’ve written a very simple PopART program using the C++ interface, but every time I try to compile it to run on an IPU device I get the following error:

terminate called after throwing an instance of ‘popart::error’ 
  what(): Could not find loss tensor ‘L1:0’ in main graph tensors

I’m defining the loss in my program like so:

auto loss = builder->aiGraphcoreOpset1().l1loss({outputs[0]}, 0.1f, popart::ReductionType::Sum, “l1LossVal”);

Is there something wrong with my loss definition that’s resulting in it being pruned out of the graph? I’ve followed the same structure as one of the Graphcore examples here.

Botje
  • 26,269
  • 3
  • 31
  • 41
Niels
  • 149
  • 8

1 Answers1

4

This error usually happens when the model protobuf you pass to the TrainingSession or InferenceSession objects doesn’t contain the loss tensor. A common reason for this is when you call builder->getModelProto() before you add the loss tensor to the graph. To ensure your loss tensor is part of the protobuf your calls should be in the following order:

... 
auto loss = builder->aiGraphcoreOpset1().l1loss(...); 
auto proto = builder->getModelProto(); 
auto session = popart::TrainingSession::createFromOnnxModel(...); 
...

The key point is that the getModelProto() call should be the last call from the builder interface before setting up the PopART session.

Manuel Lopez
  • 76
  • 5