Mesh size large the results is incorrect, while the size small, the results is nan

Please read Read before posting: How do I get my question answered?

I’ve edited your post because the code was incorrectly formatted, to the point of being unreadable. Please edit it back making sure that the code is within “```” so that it typesets nicely as

def my_function(a,b):
   return a + b

Furthermore, give more context of what you are trying to do. One sentence is not enough.