A weird kink in CLASS matter power spectrum

[yicizhong98]

Hi! I'm currently using CLASS to generate matter power spectrum, but it appears a weird kink at low \ell (please see the figure attached below ), which is not within our expectation...I'm kind of wondering if you have any idea of where it comes from, and how to resolve it?

Thanks in advance, Yici

P.S., Here is my python code to generate this matter power spectrum:

OmegaB = 0.0486 OmegaM = 0.2603 h=0.6774 ombh2 = OmegaB*h*2 omch2 = OmegaMh**2 sigma8 = 0.8159 n_s = 0.9667

z1 = 0.11111111111111116 z2 = 0.09890109890109877 z_s = (z1 + z2)/2 lmax = 12288

LambdaCDM = Class() LambdaCDM.set({'omega_b':ombh2,'omega_cdm':omch2,'h':h,'sigma8':sigma8,'n_s':n_s})

LambdaCDM.set({'output':'mPk,nCl', 'lensing':'no', 'P_k_max_1/Mpc':100.0, 'z_pk':0.0, 'reio_parametrization':'reio_camb', 'selection':'tophat', 'selection_mean':z_s, 'selection_width': (z1-z2)/2, 'l_max_lss':lmax, 'non linear':'halofit' }) LambdaCDM.compute() cls2=LambdaCDM.density_cl(lmax) ell_th=cls2['ell'][2:] cldd_th=cls2['dd'][0][2:] plt.loglog(ell_th,cldd_th,label='Classy theory') plt.xlabel('$\ell$') plt.ylabel('cldd') plt.legend()

[schoeneberg]

Dear @yicizhong98 , this is expected. This is simply the limber approximation that is applied at too low L. Set also LambdaCDM.set({'l_switch_limber_for_nc_local_over_z':1000, 'l_switch_limber_for_nc_los_over_z':1000}) and it works (at least for me)

[kcroker]

If this fixed your issue @yicizhong98 , could you please Close it?

[yicizhong98]

Thanks!! That fixed everything. Sorry that I forgot to close it.