[CosmoMC/Planck likelihood] Precision

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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Luke Hart
Posts: 42
Joined: July 13 2015
Affiliation: University of Manchester

[CosmoMC/Planck likelihood] Precision

Post by Luke Hart » November 20 2018

Dear all,

Does anyone know how precise the Planck likelihood values that we get out of CosmoMC are? When looking at analysis with the likelihood values, it's really important to know what the actual precision is so we don't get dominated by noise in the numerical analysis. Does anyone know how accurate the likelihood values are (i.e. of the 6466.xxxxxx for the best fit value I have for a given parameter set, what is the number of d.p. one can go to before this becomes noise dominated)?

Thanks in advance for your help

Luke

Antony Lewis
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Affiliation: University of Sussex
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Re: [CosmoMC/Planck likelihood] Precision

Post by Antony Lewis » November 21 2018

The noise is the likelihood itself is small. However there will be numerical noise in the parameters of the best-fit point, which can be O(1).

Luke Hart
Posts: 42
Joined: July 13 2015
Affiliation: University of Manchester

Re: [CosmoMC/Planck likelihood] Precision

Post by Luke Hart » December 05 2018

Thanks Antony, but I just wanted to ask: what do you mean when you say 'O(1)' ??

Antony Lewis
Posts: 1394
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: [CosmoMC/Planck likelihood] Precision

Post by Antony Lewis » December 06 2018

I mean chi^2 can move around by O(1) depending on where exactly the minimizer ends up (though usually stable to somewhat below \pm 1).

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