Name of parameters

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Jack Sparrow
Posts: 14
Joined: May 12 2016
Affiliation: HK

Name of parameters

Post by Jack Sparrow » May 15 2016

I want to ask a very naive question about cosmomc. There are different parameters in camb and cosmomc. But the name seems to be different. For example, in camb, spectral index is tensor_spectral_index(1) (actually I also don't know the meaning of 1 in bracket)and in cosmoc it is nt. So, what is the difference?

Besides, I want to vary the tensor amplitude in cosmomc. What should I do and what is the name for it, tensor_amp or A_t?

Thanks a lot.

Antony Lewis
Posts: 1941
Joined: September 23 2004
Affiliation: University of Sussex
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Re: Name of parameters

Post by Antony Lewis » May 15 2016

No difference, just different names. CosmoMC supports a generic mapping between cosmological parameters and cosmology code, so names can be different (and you don't have to use CAMB, e.g. can use PICO).

Jack Sparrow
Posts: 14
Joined: May 12 2016
Affiliation: HK

Name of parameters

Post by Jack Sparrow » May 16 2016

Thanks a lot.

But I have another question. How can I vary the tensor amplitude? Can I use parameter param[AT] directly? It seems that this doesn't work since AT is a derived parameter. So, I use the param[r], but it is still not correct. In the power_tilt.f90 file, I print the value P%TensorPowerAmp(ix), the result is 1. I don't know why? There seems to be different parameterization methods. Did I configure it incorrectly?

Thanks.

Jack Sparrow
Posts: 14
Joined: May 12 2016
Affiliation: HK

Name of parameters

Post by Jack Sparrow » May 17 2016

Thanks a lot, Antony Lewis!

Actually, I have another question now. I have a test run of my model. My model is about the tensor power spectrum. The result of chains is a little strange, because the amplitude of tensor power spectrum has some preferred non-zero value and the preferred region is not around zero. So, it implies we see gravitational waves? Of course, this is not reasonable. So, what is the problem? BTW, my test only have 15000 steps. Is this caused by my limited steps or are there some other reasons?

Thanks a lot.

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