Solved by Yaroslav_Bulatov in post #6 
              
              
                What if you use the same repeat trick for forward mode? IE, replicate x and v vector and do the same as in reverse mode? 
https://colab.research.google.com/drive/1tcm7Lvdv0krpPdaYHtWe7NA2bDbEQ0uj#scrollTo=-jwISHOycQ8x