Solved by ptrblck in post #4 
              
              
                I’m not sure I understand the use case correctly and what “feature” maps refer to in this case, but this might work: 
a = torch.zeros(2, 3, 4)
a[1] = 1.

b = torch.ones(2, 3, 4) * 2
b[1] = 3

c = torch.cat((a, b), dim=1)
print(c)
> tensor([[[0., 0., 0., 0.],
           [0., 0., 0., 0.],
           […