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Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

Negative chi^2 from Commander
 
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Björn Sörgel



Joined: 05 Apr 2013
Posts: 13
Affiliation: Institute of Astronomy/Kavli Institute for Cosmology Cambridge

PostPosted: October 22 2013  Reply with quote

Dear all,
when I run with feedback=3, the following LnLike and Chi2 are printed for the individual datasets:

Code:

Calling CAMB
 CAMB done
 lowlike_v222.clik lnlike =    1007.28444991537     
 DR7 BAO likelihood =    1.91087739414207     
 6DF BAO likelihood =   1.449826393350034E-002
 DR9 BAO likelihood =   5.291717134685368E-002
 commander_v4.1_lm49.clik lnlike =   -3.74495218656174     
 CAMspec_v6.2TN_2013_02_26_dist.clik lnlike =    4192.16885357843     
   1007.284   2014.569   CMB: lowlike_v222.clik
      1.911      3.822   BAO: DR7
      0.014      0.029   BAO: 6DF
      0.053      0.106   BAO: DR9
     -3.745     -7.490   CMB: commander_v4.1_lm49.clik
   4192.169   8384.338   CMB: CAMspec_v6.2TN_2013_02_26_dist.clik


Why is there a negative chi2 from commander? And secondly, isn't the BAO chi2 very low?. I first discovered this in a modified Jun2013 version, but I could reproduce it with a vanilla Oct2013 one.

Cheers,
Björn
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Antony Lewis



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

PostPosted: October 22 2013  Reply with quote

The normalization of the likelihoods is arbitrary (constant offsets in the log like don't matter); they could have added a constant offset to the commander likelihood to make it look like a χ2 but didn't.
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Björn Sörgel



Joined: 05 Apr 2013
Posts: 13
Affiliation: Institute of Astronomy/Kavli Institute for Cosmology Cambridge

PostPosted: October 22 2013  Reply with quote

Dear Antony,
thanks for the quick reply. "Problem" solved.

Cheers,
Björn
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Luke Hart



Joined: 13 Jul 2015
Posts: 25
Affiliation: University of Manchester

PostPosted: August 02 2017  Reply with quote

Antony Lewis wrote:
The normalization of the likelihoods is arbitrary (constant offsets in the log like don't matter); they could have added a constant offset to the commander likelihood to make it look like a χ2 but didn't.


Antony, it seems that if you try and run GetDistGUI.py with this dataset, it won't let you view the .margestats or the Parameter tables due to the negative chi2 from commander? Anyway you can think of getting around this??

Luke
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Antony Lewis



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

PostPosted: August 02 2017  Reply with quote

You need to edit the .ranges file for the chain, and remove the 0 N range for chi2_xxx where xxx is the likelihood.
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Luke Hart



Joined: 13 Jul 2015
Posts: 25
Affiliation: University of Manchester

PostPosted: August 02 2017  Reply with quote

Fantastic thank you :)
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