[SciPy-User] curve_fit error: Optional parameters not found...

[Jeremy Conlin]

I downloaded scipy 0.8b1 yesterday; I was excited to try out the new
curve_fit function.  Today I have been playing with it and some of the
time it works.  Other times I get the error:

RuntimeError: Optimal parameters not found: Both actual and predicted
relative reductions in the sum of squares
  are at most 0.000000 and the relative error between two consecutive
iterates is at
  most 0.000000

I know this has been discussed before (see
http://mail.scipy.org/pipermail/scipy-user/2009-August/022088.html),
but apparently has not been fixed.

Can someone explain why I get this error and how I can avoid it?

Thanks,
Jeremy