Solved by a3VonG in post #2 
              
              
                In short: 
A = torch.tensor([1,0])
B = torch.tensor( [ [1,2,3] , [4, 5, 6] ] )
A = A.unsqueeze(1)
C = A * B
print(C)

Which gives as output: 
C = tensor([[1, 2, 3],
        [0, 0, 0]])

You can use broadcasting for these type of problems.