How to define two functions run simultaneously within a function?

[Alberto]

Alright, I may not be of help to the general solution, but I can give you some pointers which hopefully will prove useful:

• Value_2 is not set prior to be used by call1, as indicated in your OP, if that makes sense you can set an initial value prior to the loop being executed for the first time;
• dilution is set but never used
• Value_1 is used but never set
• Value_2 is calculated using Value_1 + call*M where call is list, not a scalar. Did you mean to use call1 ?
• If Value_1 and Value_2 are floats, it's possible that they may be close enough for your needs but that they will not equal 0. I would suggest storing the result without comparing to 0 so that you can observe yourself if one of the iterations is good enough for your needs.

Thank you! I changed the code the way you proposed, but the thing is that call1 and Value_2 are interdependent. So, I do not know how to deal with this. Once I run the code above I got constant diff_df and call_df since Value_2 is not changing. Any suggestions how can I make Value_2 be used for the first interation and all the rest should use new Value_2?