Up until now, Genfit is uniquely wrt "Conjugate Gradient".
Thus, very difficult to initialize. Sometimes quick optimize
sometimes needs lot of manual iterations. Not so magnificient
than Mathcad/Mathsoft "Minerr LM".
Many models [especially some that I designed] are very reactive,
no maths will do except the "piano maths" from the keyboard.
The residuals bar plot is gorgeous for deciding the fit.

Jean

Genfit Hysteresis.sm (37 KiB) downloaded 60 time(s).

... this one converges in 3 steps.

Genfit Hysteresis OTHER.sm (38 KiB) downloaded 62 time(s).