CAMB

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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Josh Kable
Posts: 2
Joined: March 21 2018
Affiliation: Johns Hopkins University

CAMB

Post by Josh Kable » March 21 2018

I am attempting to calculate the parameter covariance matrix from a Fisher matrix generated by finite difference differentiation of the TT Cls generated by CAMB; however, I seem to be running into a problem with the accuracy of the final digit outputted into the text file. Namely, my derivative power spectrum seems to have a blocky structure, particularly near the peaks, which is consistent with CAMB generated Cls that are not sufficiently accurate for the step size of my derivative. I have tried a larger step size, and that problem goes away; however, the calculated covariance matrix becomes very sensitive to changes in the step size indicating that it is not very accurate. What accuracy settings should I edit in the params.ini file to increase the accuracy of the outputted Cls? Do I also need to edit CAMB?

Antony Lewis
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Joined: September 23 2004
Affiliation: University of Sussex
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Re: CAMB

Post by Antony Lewis » March 24 2018

If you use the python wrapper you can avoid the text files. There are three accuracy parameters you can change, either in the .ini file or in via the python wrapper.

Josh Kable
Posts: 2
Joined: March 21 2018
Affiliation: Johns Hopkins University

CAMB

Post by Josh Kable » March 26 2018

What are the three accuracy parameters that you mentioned? What do each of them do, and do you have any suggestions as to which ones I should change in this case?

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

CAMB

Post by Luke Hart » March 29 2018

Hey Josh,

The AccuracyBoost parameter is a generic accuracy parameter which affects a lot of stuff such as the k precision in the power spectra and the timestep precision when computing things like recombination and reionization.

The LAccuracyBoost parameter adds to the terms evaluated in the hierarchy and LSampleBoost increases the number of l values in the interpolation.

Readme for the CAMB Accuracy stuff

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