COSMOMC as a generic sampler

Use of Healpix, camb, CLASS, cosmomc, compilers, etc.
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Bruna Santos
Posts: 3
Joined: February 10 2009
Affiliation: Centro Astrofisica UP

COSMOMC as a generic sampler

Post by Bruna Santos » July 19 2009

Deal All,

I'm trying to use COSMOMC as a generic sampler, but I'm having some problems. As mentioned in http://cosmologist.info/cosmomc/readme.html, I've preformed the changes require, but I don't know how to change the GenericLikelihoodFunction and then running it. Could anyone help me with this, by giving me a specific example? I also downloaded Cosmologui, but I' don't know if this is produces the same results than using COSMOMC as a generic sampler. And I would like to know if in cosmologui it is possible to change the likelihood function and how to do it.

Could anyone help me with this question by giving me a specific example?

Thank you all,

Bruna Santos

Antony Lewis
Posts: 1503
Joined: September 23 2004
Affiliation: University of Sussex
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Re: COSMOMC as a generic sampler

Post by Antony Lewis » July 20 2009

Cosmologui is for looking at samples, not generating them.

GenericLikelihoodFunction is in CalcLike.f90.

Bruna Santos
Posts: 3
Joined: February 10 2009
Affiliation: Centro Astrofisica UP

COSMOMC as a generic sampler

Post by Bruna Santos » July 20 2009

Thank for your help, Antony.

Could anyone say to me how put the function and params in CalcLike.f90?

Could anyone help me with this question by giving me a specific example?

Thank you all,

Bruna Santos

Tess Jaffe
Posts: 7
Joined: March 11 2005
Affiliation: Centre d'Etude Spatiale des Rayonnements

COSMOMC as a generic sampler

Post by Tess Jaffe » July 21 2009

I'm not sure exactly what you're asking, but I just modified the GenericLikelihoodFunction function in calclike.f90 around line 35. You take out the lines

GenericLikelihoodFunction = LogZero
stop 'GenericLikelihoodFunction: need to write this function!'

and instead add lines like

call my_like(Params%P,num_hard,thisval)
GenericLikelihoodFunction = thisval

The function "my_like" should expect a pointer to float type (i.e. a list of floats) as the first parameter, an integer specifying how many parameters there are (hard-wired), and lastly a pointer to a float where it should return the value of -ln(likelihood).

I'm no Fortran programmer, so in my case, my_like is a C++ function. But it's the same in that you just then link in the corresponding object file when you compile cosmomc.

Does that answer your question?

Shaun Thomas
Posts: 3
Joined: October 26 2006
Affiliation: University College London (UCL)

COSMOMC as a generic sampler

Post by Shaun Thomas » July 22 2009

In calclike.f90 I have:


contains

function GenericLikelihoodFunction(Params)
type(ParamSet) Params
real :: GenericLikelihoodFunction

call lensing_likelihood(Params%P(1),Params%P(2),GenericLikelihoodFunction)
print *, 'genericlikelihood is:', GenericLikelihoodFunction

end function GenericLikelihoodFunction


This likelihood function is a C++ function of mine and so I'd define it:


extern "C" {

void lensing_likelihood_(float *omega_m, float *sigma_8, float *result){

double log_likelihood;
[do some stuff]

*result = (float)log_likelihood;
}
}

elsewhere in my code. In settings.f90 make sure you have something like:

logical, parameter :: generic_mcmc= .true.
integer, parameter :: num_hard = 2
integer, parameter :: num_initpower = 0
integer, parameter :: num_norm = 0

where 2 is the number of parameters (for example) you have in your function (Params%P(1),Params%P(2))

Remember to compile with Makefile_nowmap and you'll still need to compile camb. If you're still having issues try checking you have,

use_CMB = F
use_HST = F
use_mpk = F

in your params.ini. As stated above cosmoloGUI will just analyse your chains. It doesn't care what they are - wmap, crop circle distribution...

good luck - shaun

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