CosmoCoffee

Dear all,

In CAMB I can set re_use_optical_depth and re_optical_depth in ./CAMB/params.ini

re_use_optical_depth = T
re_optical_depth = 0.04

But When I use MCMC, I don't know how to set these two parameters.
And if I don't modify anything the default is

re_use_optical_depth = F
re_optical_depth = 0

Now I want to set these two parameters

re_use_optical_depth = T
re_optical_depth = 0.04

How to do this?

Thanks!

Jun-Qing Xia

Hi.

When you're running CosmoMC the 'params.ini' for CAMB, i.e., the one in /CAMB, is not used at all.
Instead, the values for the parameters are given in the 'params.ini' for CosmoMC.

In case of fixed optical depth, \tau=0.04, you just set 'param4' in 'params.ini' to 0.04 0.04 0.04 0 0.
Actually, the min and max values (2nd and 3rd number) can be anything, as long as 0.04 is
in that interval and the start and propose widths are zero so that \tau doesn't wander away from
its starting position. This of course works similarly for all the other parameters as well.

Hope this helps.

Vesa

Hi,

If I set the param4 like this

param4 = 0 0 0 0 0

will the parameter re_use_optical_depth be set as F automatically?

And when setting param4 = 0.17 0.01 0.8 0.07 0.04

re_use_optical_depth will be change to T automatically?

Thanks!

Jun-Qing Xia

In the first case it sets tau to zero (so more like use_optical_depth=F; z_re=tau=0).

The default CosmoMC parameterization always uses the optical depth, not reionization redshift (so internally it does set re_use_optical_depth=T, yes). See the alternative params_H download in the readme if you want to use z_re instead.