Solved by ptrblck in post #2 
              
              
                Not the values in the array/tensor are negative but the strides, which are used to access elements in the tensor via indexing. 
Negative strides are not supported in PyTorch, so you would have to create a copy first: 
x = torch.randn(10, 10)
x[:, ::-1]
# > ValueError: step must be greater than zero…