Cobaya minimizer question

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Helena Garcia
Posts: 17
Joined: October 05 2021
Affiliation: UCI

Cobaya minimizer question

Post by Helena Garcia » January 21 2022

I want to run minimization over the calculated chains using mcmc with cobaya and I don't know where you I write the path of the chains so that the program can use them to do a more precise minimazation? Thanks!

Antony Lewis
Posts: 1842
Joined: September 23 2004
Affiliation: University of Sussex
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Re: Cobaya minimizer question

Post by Antony Lewis » January 21 2022

You need to do a minimization run to find a minimum, you can't find a global minimum from chains since in high dimensions there are almost no samples near the posterior peak.

Helena Garcia
Posts: 17
Joined: October 05 2021
Affiliation: UCI

Re: Cobaya minimizer question

Post by Helena Garcia » January 21 2022

Thanks for your answer!
I am running nested models, for example, LCDM and the LCDM + w free, therefore, I'm expecting a better fit for the model that has more freedom (in this case LCDM+w. Nevertheless, when I run minimizer over this two models, I get a smaller minuslogpost (in absolute magnitude) for the LCDM than for the LCDM + w free, which is mathematically inconsistent. I have ran the full chains since I thought it was necessary in order to run the minimizer.

How I set up the minimizer run is by changing the last part in the .yaml file (instead of mcmc sampler):

Code: Select all

sampler:
  minimize:
    method: bobyqa
    ignore_prior: False
    max_evals: 1e6d
    best_of: 2
    confidence_for_unbounded: 0.9999995
Is this the way to proceed or am I doing something wrong? How should one set this run?

Thanks in advanced!

Antony Lewis
Posts: 1842
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

Re: Cobaya minimizer question

Post by Antony Lewis » January 21 2022

Looks OK. You can make use of your chains by setting the minimizer "covmat" to the covariance matrix from your chains. The minimizer may work much better with a sensible covmat.

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