Reverted the logic, that the chi2 Jacobian should be used.
Instead, the direct Jacobian exponential is used instead.
When fitting with the estimated errors from the Direct Jacobian, the results are MUCH better, and comparable to 2000 Monte-Carlo simulations.
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 2014-08-28
Parent: [r25410]
Child: [r25412]
