Solved by I3aer in post #4 
              
              
                Hi, 
I have solved the problem. I have changed the name of the updated laplacian in the network. I named both that tensor and the input tensor with the same name ‘laplacians’. In addition, I’ve changed the addition-assignment to addition, i.e., 
laplacians += res_laplacians  → u_laplacians = laplaci…