I'm doing research about a model with nontanh reionization history. I already changed the function Reionization_xe in reionization.f90, but now I'm not sure about the value of ReionHist%tau_start. The comment says it's the time when xe is 'very small', how should I change it if the reionization history is not tanh anymore?
Another question is about the calculation of actual_opt_depth. I've read the subroutine inithermo but I don't understand how it's calculated. What is the theory behind this value? Any recommended readings?
CAMB: replacing reionization history

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Re: CAMB: replacing reionization history
Any value where your x_e is very small should be OK (e.g. 1e4).
The "actual" optical depth is the calculated optical depth due to reionization (which may differ from input value since that is mapped approximately onto a reionization redshift). It's the integral using the difference of the total x_e to the x_e there would be with no reionization (so is well defined, not depending on an arbitrary highz cutoff, and zero when no reionization even though there is finite scattering due to the ~2e4 ionization fraction left from recombination).
The "actual" optical depth is the calculated optical depth due to reionization (which may differ from input value since that is mapped approximately onto a reionization redshift). It's the integral using the difference of the total x_e to the x_e there would be with no reionization (so is well defined, not depending on an arbitrary highz cutoff, and zero when no reionization even though there is finite scattering due to the ~2e4 ionization fraction left from recombination).