Identified here #53 MATLAB is 1 indexed so -index represents all indices EXCEPT for the one listed. However since python is 0 index -0 is the same as 0 so there is an ambiguity. One proposal is tensor.ttm(dims=None, exclude_dims=None). Would need to see if this ambiguity is the same throughout other tensor implementations and should be updated uniformly/checked in algorithms that use the tensors.