Hello everyone,
I'm working on a project where I need to modify CAMB to account for a model in which the Omegas are factored differently (adding more parameters), but only in the context of background dynamics. That is, I want to modify the form of the Hubble parameter without affecting the actual fluid densities.
After some initial research, it seems that the `equation.f90` file might be relevant to this modification. However, I'm unsure about where I need to change this file and whether there are other parts of the code that should also be adjusted.
I would greatly appreciate any guidance or suggestions.
Thank you very much for your help!
CAMB: Modifications for Altered Background Dynamics

 Posts: 12
 Joined: June 02 2024
 Affiliation: Weizmann Institute of Science

 Posts: 1980
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 Affiliation: University of Sussex
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Re: CAMB: Modifications for Altered Background Dynamics
The help assistant can answer this one (help_assist.php)
Modify dtauda Subroutine: The subroutine dtauda(a) in equations.f90 returns dt/da and is used wherever the background evolution is needed. You can modify this subroutine to implement your new model for the Hubble parameter【4:0†source】.

 Posts: 12
 Joined: June 02 2024
 Affiliation: Weizmann Institute of Science
Re: CAMB: Modifications for Altered Background Dynamics
Thank you very much! :)

 Posts: 12
 Joined: June 02 2024
 Affiliation: Weizmann Institute of Science
Re: CAMB: Modifications for Altered Background Dynamics
Hi Antony,
I hope you're doing well.
I've been exploring the `dtauda(a)` subroutine in `equations.f90`, and I’m having some trouble understanding how to proceed with my modifications. Specifically, I’m looking to define effective densities for radiation and matter, relevant only to background dynamics.
From what I can gather, it seems like I might need to adjust `grhoa2` by modifying `this%grho_no_de(a)`. However, I’m unclear on the exact meaning of `this%grho_no_de(a)`, and I couldn’t find where `grho_no_de(a)` is defined.
If you could provide any guidance or point me in the right direction, I would be very grateful. To make it easier, I’ve included the part of `equations.f90` where the `dtauda(a)` subroutine is defined:
Thank you so much for your time and assistance.
Best regards,
Dror
P.S. The comment before `dtauda(a)` in `equations.f90` says:
Is `dtauda(a)` calculates dt/da or d[math]/da?
I hope you're doing well.
I've been exploring the `dtauda(a)` subroutine in `equations.f90`, and I’m having some trouble understanding how to proceed with my modifications. Specifically, I’m looking to define effective densities for radiation and matter, relevant only to background dynamics.
From what I can gather, it seems like I might need to adjust `grhoa2` by modifying `this%grho_no_de(a)`. However, I’m unclear on the exact meaning of `this%grho_no_de(a)`, and I couldn’t find where `grho_no_de(a)` is defined.
If you could provide any guidance or point me in the right direction, I would be very grateful. To make it easier, I’ve included the part of `equations.f90` where the `dtauda(a)` subroutine is defined:
Code: Select all
function dtauda(this,a)
use results
use DarkEnergyInterface
implicit none
class(CAMBdata) :: this
real(dl), intent(in) :: a
real(dl) :: dtauda, grhoa2, grhov_t
call this%CP%DarkEnergy%BackgroundDensityAndPressure(this%grhov, a, grhov_t)
! 8*pi*G*rho*a**4.
grhoa2 = this%grho_no_de(a) + grhov_t * a**2
if (grhoa2 <= 0) then
call GlobalError('Universe stops expanding before today (recollapse not supported)', error_unsupported_params)
dtauda = 0
else
dtauda = sqrt(3 / grhoa2)
end if
end function dtauda
Best regards,
Dror
P.S. The comment before `dtauda(a)` in `equations.f90` says:
Code: Select all
! Background evolution, return d tau/ d a, where tau is the conformal time

 Posts: 1980
 Joined: September 23 2004
 Affiliation: University of Sussex
 Contact:
Re: CAMB: Modifications for Altered Background Dynamics
it is $d\tau/d a$. The grho_no_de function definition is commented in the source to describe what it is.