Fix to eksperimental class for fitting with different methods. After moving the funciont into class, 'self' should be added to the funcion.
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 2014-08-29
Parent: [r25468]
Child: [r25470]
