Solved by KFrank in post #3 
              
              
                Hiiiii Sakuraiiiii! 

The short answer is that Softmax isn’t the right way to enforce your 
constraint. 
The medium-short answer is that you’re getting almost the right 
answer, but for the wrong reason. 
The somewhat longer short answer is that Softmax isn’t the right 
way to enforce your constrain…