@Kiriakos_Shiarli I implemented a CTC that computes gradients via pure autograd (it’s quite slow):

  
      
      GitHub
  
  
    

vadimkantorov/ctc 10

Primer on CTC implementation in pure Python PyTorch code - vadimkantorov/ctc


  
  
    
    
  
  


If you replace logadd by PyTorch logsumexp and use 1e-16 instead of float(’-inf’), double backward may just happen to work