fix a problem with python code having to do symbolic regression -- 2

Hi,

I have a "main.py" file that does symbolic regression and output the minimum fitness as it works.

there is a file called "regression.txt" that is the input of the application.

although the fitness is suppose to be monotonously decreasing there are times where the output fitness is increasing.

You need to:
1. find the bug.
2. fix the code so it wont happen.

note:
I use python 3.9
.