3 things:
1: It's not an error, just a warning for guidance. It doesn't prevent the code from being run.
2: It's correct. ep and mu are assigned a value, and then the function exits. The values are never used, nor are any of the output arguments given a value. gather, tout, etc need to be assigned a value. I'm assuming that once this function is done being written, the values assigned to ep and mu will be used to calculate those output arguments. At that point, all the squiggly lines will be gone.
3: In the future, please just paste the code in a formatted block in your post. That way people can run it if they need to, or they can copy/paste sections of it for explanation.
