### CAMB: question on extra evolution variable

Posted:

**June 13 2019**Hi Anthony,

I added a set of extra evolution variables for dark radiation, and I have some concerns about my practice here.

What I did was to add EV%dr_ix as the equation index of dark radiation, and add the same number of equations as massless neutrino in subroutine 'SetupScalarArrayIndices', then did adjustments to subroutine 'initial' and derivs. If my understanding is right, now when I'm doing GaugeInterface_EvolveScal(EV,tau,y,State%Transfer_Times(itf),tol1,ind,c,w), y variable has clx,q,pi for all components including my extension for dr, but since I did nothing to EV%OutputTransfer, I won't get the transfer data of dr in the end.

My question is, will this practice mess up the output of other transfer functions? Is not getting dr perturbation evolution the only aftermath that I didn't do OutputTransfer and only adapting 'y' structure in the code? Specifically, I was worried about that EV%OutputTransfer components mismatching the differential equation components would cause some transfer data to be put into wrong boxes.

Thanks,

Angela

I added a set of extra evolution variables for dark radiation, and I have some concerns about my practice here.

What I did was to add EV%dr_ix as the equation index of dark radiation, and add the same number of equations as massless neutrino in subroutine 'SetupScalarArrayIndices', then did adjustments to subroutine 'initial' and derivs. If my understanding is right, now when I'm doing GaugeInterface_EvolveScal(EV,tau,y,State%Transfer_Times(itf),tol1,ind,c,w), y variable has clx,q,pi for all components including my extension for dr, but since I did nothing to EV%OutputTransfer, I won't get the transfer data of dr in the end.

My question is, will this practice mess up the output of other transfer functions? Is not getting dr perturbation evolution the only aftermath that I didn't do OutputTransfer and only adapting 'y' structure in the code? Specifically, I was worried about that EV%OutputTransfer components mismatching the differential equation components would cause some transfer data to be put into wrong boxes.

Thanks,

Angela