Hi Aasif, you are welcome.
Here is the explanation I think is correct: BER is a value between 0 and 1, so putting the tolerance (which is the difference between the target and the value reached during iterations) at 0.5 does not make too much sense and probably causes the optimization to not converge. A very small value like the 1e-30 that I tried instead allows for the optimization to work.
Let me know if my explanation is clear enough.
Regards,
Alessandro