CosmoCoffee

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

Dear all,
I was trying to generate the weak lensing convergence power spectra $C_l^{\kappa\kappa}$ given some window functions. I got a 8-column output Cl file by choosing 1 redshift bin and setting

get_scalar_cls = T
get_transfer = F
get_vector_cls = F
get_tensor_cls = F
want_CMB = T

To my understanding, the 8 output columns should be
l, $Cl^{TT,TE,EE},Cl^{\phi\phi}, Cl^{T\phi}, C_l^{\kappa\kappa}, Cl^{T\kappa}$
there's no

C l B B

. Am I right?
BTW, there's a returned 'bus error' when setting nonlinear=2 (I compiled with g95).

Thanks,
Gongbo

Antony Lewis · Posted: March 08 2008

Yes, no BB for scalars.

Let me know if you find a fix for the bus error.

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

Thanks, Antony! I will let you know once I fix the problem.
BTW, the lensing source implemented in output is −2*phi*W%win_lens(j), can you provide the main reference for this issue? or some maple files.

Cheers
Gongbo

Antony Lewis · Posted: March 09 2008

−2

φ

is the standard source for the lensing potential. win_lens should be calculated consistently from your supplied source window function (Gaussian by default). Sorry I don't have any documentation.

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

Dear all,

Has anyone succeeded in reproducing some convergence power results in the literature (such as fig 2 in astro-ph/0106399) using CAMB sources? I tried but failed.

Thanks,
Gong-Bo

Antony Lewis · Posted: March 24 2008

I've checked things look consistent, though not a detailed comparison as no alternative codes to hand.

Note can set evolve_delta_xe = F to speed things up, and check stability to increasing k_eta_max_scalar. Obviously need to include non-linear corrections on small scales.

Also note limber_windows = T currently doesn't work, set limber_windows = F (any fixed welcome!)

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

Thanks Antony!
But if my window function peaks at low redshift, 0.1 for example, I have to set a huge max_eta_k, which greatly slows down the computation and might give rise to memory leaks if I have multi-bins. (I tested and found max_eta_k should be larger than 1500000 for the window peaking at z~0.1 to avoid the numerical instability).

So is it a simple solution to this problem? For example, increasing the stepsize for k integration at small scales?

Thanks,
Gong-Bo

Antony Lewis · Posted: March 30 2008

Probably need to use Limber approximation. If you get it to work please let me know.

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

But I need the cross-correlations. I tried modifying the k intervals for integration at small scales (using log-spacing rather than linear), something like that

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

After some tests, I found a fix of the Limber approximation part for lensing. The problem is the missing of a factor of l(l+1)/2 in the limber source. To get it work, do the following,
in the innermost loop in subroutine GetLimberTransfers in cmbmain.f90,
add

gongbo zhao · Joined: 04 Jan 2005 Posts: 47 Affiliation: ICG, Portsmouth

Update: The above modification only works for single lensing bin. For multi-bins, replace subroutine CalcLimberScalCls in cmbmain.f90 with the following,

Steven Pediani · Posted: October 06 2008

I'm guessing that the code has been updated since, as those subroutines don't exist in my copy of CAMB. I'm trying to generate the convergence power spectrum (like the one shown in the link posted by Gongbo Zhao), where the user is able to choose their window function, and one can work out other quantities like aperture mass and shear variance. I have done this for cmbfast, and decided it'd be useful to do the same to CAMB. I was under the impression that there was a simple relation between the convergence and the lensing potential power spectra, C

l

(κ κ)

= $\frac{1}{4}$

l 4

C

l

(φ φ)

, and so the output in the scalar file, l

4

C

l

(φ φ)

, is the convergence? I ask as I can't get it to agree with any of my other work, and so am wondering if this is not the case, or is there a subtitle change needed in one of the starting parameters.

[EDIT] Never mind, got it working now.

Lukas Hollenstein · Posted: March 31 2009

Hi,

Im also interested in the convergence power spectrum. Thanks to Gongbo Zhao for pointing out how to get the Limber approximation right. Now I think I get the right answer in the linear case.

As Gongbo already pointed out, there is a problem with the non-linear lensing. When I switch to do_nonlinear=2, I get a bus error, no matter if compiled with gfortran, g95 or ifort.

Did anybody find the problem here? Thanks!

Antony Lewis · Posted: March 31 2009

There seem to be several bugs that stop this working.

In cmbmain.f90 try changing CalcScalarSources to have some traps for j < TimeSteps%npoints:

Lukas Hollenstein · Posted: April 01 2009

Thanks Antony,

however these fixes don't help with the bus error. After digging a bit I found out that there is a problem with deallocating Pk_data in MatterPowerdata_Free (modules.f90). Commenting a few lines seems to help: