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### Omega_k and COSMOMC

Posted: **April 25 2005**

by **David Parkinson**

In the routine in cosmomc that calculates the likelihood, there is a prior on the curvature, such that Omega_k(min) =-0.3 and Omega_k(max) = +0.3. I am interested in running over a much larger prior range (-0.9 up to +1.0). Does anyone know if this prior can be extended safely, or if major modifications need to be made to the routine?

### Omega_k and COSMOMC

Posted: **April 25 2005**

by **Anze Slosar**

I think that for a very closed universe, camb will barf:

chi >= pi in closed model not supported

and give up.

### Re: Omega_k and COSMOMC

Posted: **April 25 2005**

by **Antony Lewis**

This is true. On the other hand \chi=\pi corresponds to the acoustic peak being at l=0, so with any data it is unlikely to go anywhere near there. So it will probably work for a significantly wider range of \Omega_K if you want to just edit that prior. (of course the curvature may then be implicitly bounded by the prior on H_0 and the age, so you may need to change them too).

On the other hand I haven't actually tested it on large |\Omega_K| models for years.

### Re: Omega_k and COSMOMC

Posted: **April 27 2005**

by **Anze Slosar**

Antony Lewis wrote:This is true. On the other hand \chi=\pi corresponds to the acoustic peak being at l=0, so with any data it is unlikely to go anywhere near there.

Yes, but it is enough to propose to such place for camb to stop, even though the sample would have been rejected. I remember that with pre-WMAP data this was stopping my chains even though it was clear at the time that there is no peak at l=0... So with big enough proposal width it might happen.