I'm more or less familiar with procedures and methods to fit a curve to experimental data, and I have done this many times using Matlab. However this time I have a problem that I'm not sure how to solve and I'm stuck.
I have some experimental data which I have plotted in the figure below (blue curve).
The data seem to be lowerbounded by some kind of smooth logarithmic-like curve like the red line shown in the figure (I have plotted this red curve manually using Paint just to illustrate what I mean).
I have several mathematical expressions that could be good candidates to fit the red line, but I'm not sure how to fit them in the way shown in the figure. Standard data fitting procedures use the whole data set and provide a curve somewhere in the middle of the blue curve, but I need something like the red curve.
I work with Matlab and I have tried to use the envelope function (lower envelope), the absolute value of the Hilbert transform and the convex hull (convhull) but nothing works.
Any ideas or suggestions'