CosmoCoffee Forum Index CosmoCoffee

 
 FAQFAQ   SearchSearch  MemberlistSmartFeed   MemberlistMemberlist    RegisterRegister 
   ProfileProfile   Log inLog in 
Arxiv New Filter | Bookmarks & clubs | Arxiv ref/author:

CAMB/CosmoMC: Matter Power Spectrum for w!=-1
 
Post new topic   Reply to topic    CosmoCoffee Forum Index -> Computers and software
View previous topic :: View next topic  
Author Message
Tijmen de Haan



Joined: 30 May 2013
Posts: 7
Affiliation: UC Berkeley

PostPosted: December 02 2015  Reply with quote

I'm finding significant differences between the matter power spectrum obtained through a direct CAMB call, and that available through the PK%PowerAt function in CosmoMC.

Here's the minimal way I was able to reproduce the issue:
1) I downloaded the latest version of CAMB (as of the time of this post), changed "get_transfer = T" in params.ini and plotted the contents of the resulting "test_matterpower.dat"
2) I downloaded the latest version of CosmoMC and added a print statement that prints a k array and the output of PK%PowerAt at those values of k and z=0. I compiled and ran CosmoMC with a minimal .ini file that sets the cosmological parameters to those printed out by CAMB in step 1). I copied the output and overplotted. I find that the resulting matter power spectra P(k,z=0) agree to roughly 1%.

3) I now changed only w=−1 to w=−1.5 in both the CAMB params.ini file and the CosmoMC .ini file and reran both. This results in a disagreement of nearly a factor of two around k~0.01, smoothly changing to percent level agreement at k~1.


A colleague of mine independently verified this problem. Thanks in advance for any help or insights you can offer.
Back to top
View user's profile [ Hidden ]
Antony Lewis



Joined: 23 Sep 2004
Posts: 1291
Affiliation: University of Sussex

PostPosted: December 02 2015  Reply with quote

Are you sure the parameters being used by CAMB are the same?

in Case (1) for example, CosmoMC will be setting transfer_high_precision =T (and the kmax is probably also different)

In Case(2), If you just changed the w input parameter in Cosmomc, that will change H0 at fixed theta (since theta is also another input parameter, which I assume you left unchanged?). In the CAMB .ini file, H0 is specified directly instead of theta, so you will be changing w at fixed H0 (and hence varying theta).
Back to top
View user's profile [ Hidden ] Visit poster's website
Tijmen de Haan



Joined: 30 May 2013
Posts: 7
Affiliation: UC Berkeley

PostPosted: December 03 2015  Reply with quote

After updating theta along with w in CosmoMC so as to get a consistent H0, I find the two agree at the percent level. Thanks for the help!
Back to top
View user's profile [ Hidden ]
Display posts from previous:   
Post new topic   Reply to topic    CosmoCoffee Forum Index -> Computers and software All times are GMT + 5 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group. Sponsored by WordWeb online dictionary and dictionary software.