Tried algorithms:
newton Newton-CG Steepest descent Fletcher-Reeves
None of them work.
task #7822(https://gna.org/task/index.php?7822): Implement user function to estimate R2eff and associated errors for exponential curve fitting.
Authored by: tlinnet 2014-08-25
Parent: [r25254]
Child: [r25256]
