## Cobaya: how to raise a CAMBParamRangeError or CAMBError in CAMB python scritp

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
Diogo Souza
Posts: 3
Joined: July 01 2022
Affiliation: IFT UNESP

### Cobaya: how to raise a CAMBParamRangeError or CAMBError in CAMB python scritp

Dear all,

According to the section "Modifying CAMB" (https://cobaya.readthedocs.io/en/latest/theory_camb.html?#modifying-camb) in cobaya.readthedocs we can use CAMBParamRangeError, or simply CAMBError to assign a zero likelihood when the computation of any observable would fail. In my case the observable is omega_de and the fail is omega_de<0 and the MCMC chain stop when this occurs. Therefore, to use this Cobaya functionality, what I did was to put CAMBError in the function set_params in the python module results.py. The modified results.py is

Code: Select all

    def set_params(self, params):
"""
Set parameters from params. Note that this does not recompute anything;
you will need to call :meth:calc_transfers if you change any parameters affecting the
background cosmology or the transfer function settings.

:param params: a :class:~.model.CAMBparams instance
"""
self.Params = params
if (self.omega_de < 0):
raise CAMBError('omega dark energy is negative, assigning 0 likelihood')

However, that did not work and the chain stopped due to omega_de<0. I am using CAMBError at the right place?. If yes, why this is not working? If no, where is the right place to use CAMBError in order to assign a zero likelihood for omega_de<0?

Thank you very much.

Antony Lewis
Posts: 1852
Joined: September 23 2004
Affiliation: University of Sussex
Contact:

### Re: Cobaya: how to raise a CAMBParamRangeError or CAMBError in CAMB python scritp

You seem to be checked before any parameters are actually set in that function