Strange result for ion drift velocity in low pressure propane, missing long. diffusion coefficient

Hi,
I made a few changes trying to improve the interpolation/extrapolation of the ion velocity:

I will run a few checks and then merge to the master branch.

Using this branch, and the following script/options I got a (somewhat) more reasonable shape for the ion velocity.

import ROOT
import Garfield

gas = ROOT.Garfield.MediumMagboltz()
gas.LoadGasFile('C3H8_1Torr_313K_0.1_to_1800.gas')
gas.SetExtrapolationMethodIonMobility("constant", "exponential")
gas.LoadIonMobility('IonMobility_C3H8+_C3H8.txt')
gas.PrintGas()

view = ROOT.Garfield.ViewMedium(gas)
cV = ROOT.TCanvas('cV', '', 600, 600)
view.SetCanvas(cV)
view.PlotIonVelocity()

Not an ideal solution, but perhaps a work-around…

Thank you very much!