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Name of parameters
 
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Jack Sparrow



Joined: 12 May 2016
Posts: 14
Affiliation: HK

PostPosted: May 15 2016  Reply with quote

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 At?

Thanks a lot.
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Antony Lewis



Joined: 23 Sep 2004
Posts: 1278
Affiliation: University of Sussex

PostPosted: May 15 2016  Reply with quote

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).
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Jack Sparrow



Joined: 12 May 2016
Posts: 14
Affiliation: HK

PostPosted: May 16 2016  Reply with quote

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.
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Jack Sparrow



Joined: 12 May 2016
Posts: 14
Affiliation: HK

PostPosted: May 17 2016  Reply with quote

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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