How to fit to part of plot and extrapolate, all on the same plot

I would like to fit an exponential curve to a part of my data, and then extrapolate it on the same data plot, to find where it levels out. To visualise my question see this figure - the dashed V-extrapolated is an exponential fit to part of the data, plotted on the same figure, this is exactly what I want.

The only way I know how to do this, is by creating a separate dataset, which includes the portion of data I want to fit, and then apply fit(xtoFit,ytoFit, expFit). This works, but shows only the fitted part of data, without extrapolation and I do not know how to plot this on my original plot:

 How to I combine the two steps to show full data, exponential fit, and its extrapolation, all on single graph?
Any help would be appreciated!

[Kuifeng]

 %try this function: 
help plotyy, %'Graph with Multiple x-Axes and y-Axes'

[IJ]

Hi, I tried that, thanks.

The problem is, the fitted data only show at the exact points of fitting. I would like to see the extrapolated rest of this fitted curve on my plot.

Answer 1

[Star Strider]

An single exponential function will ‘level out’ at infinity.

The paper refers you to the model in ‘A unified model of CA1/3 pyramidal cells: an investigation into excitability’ Prog Biophys Mol Biol. 2011 Mar;105(1-2):34-48. It’s behind a paywall (as is essentially everything Elsevier publishes), so I can’t look at it. I would use and fit that model if you want to fit your data and find its characteristics.