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External power spectrum in cosmomc
 
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Jack Sparrow



Joined: 12 May 2016
Posts: 9
Affiliation: HK

PostPosted: May 12 2016  Reply with quote

Recently, I am trying to work out some parameter constraints on my model. I need to input the power spectrum into cosmomc. The power spectrum has some parameters which can determine the shape. I don’t know how to input the function of power spectrum and then constrain the value of parameters. I know in monte python, there is a file external_Pk which can do this. So, how about cosmomc?

Another question is how to fix the value of parameters in cosmomc,especially the nuisance parameters?

Thanks!
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1224
Affiliation: University of Sussex

PostPosted: May 13 2016  Reply with quote

You need to write your own power spectrum module to replace power_tilt.f90 in CAMB. If it has the same numbers of parameters as the standard model, you can probably just reinterpret ns, nrun, etc as your new parameters and just use them from CosmoMC as normal. Otherwise you'll need to modify Cosmomc to propagate your parameters in the same way that ns, nrun etc are at the moment.

You can use

Code:
param[name]= x

in the .ini file to fix parameter named name to the value x.
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Jack Sparrow



Joined: 12 May 2016
Posts: 9
Affiliation: HK

PostPosted: May 13 2016  Reply with quote

Thank you very much!

Since I am new to cosmomc and also fortran, could you please tell me more details on how to make relevant changes in cosmomc?

Thanks a lot!
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1224
Affiliation: University of Sussex

PostPosted: May 13 2016  Reply with quote

It's partly covered in the FAQ
http://cosmologist.info/cosmomc/readme.html#FAQ
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