Solved by CesMak in post #4 
              
              
                I think I now found the solution: 
Sequential is automatically doing the job for you if you have a 2d input matrix 
whereas torch.cat has to be adopted! 
minimal working code 
import torch
import torch.nn as nn
class ActorMod(nn.Module):
    def __init__(self, state_dim, action_dim, n_latent_var):
 …