CosmoMC: Accuracy of post-process
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- Posts: 73
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CosmoMC: Accuracy of post-process
Dear all,
Has anyone test the accuracy of post-process? If some of the parameter space is not sampled by the original run but allowed by the latter constraint (pointed out by Hiranya Peiris), is the result still correct?
For example, are the following two results both correct?
I) Run MCMC with CMB+LSS+SN to generate *.data and then post process to give constrains of CMB+SN.
II) Run MCMC with CMB+SN to generate *.data and then post process to give constrains of CMB+SN+LSS.
I guess II) should be more accurate.
Am I right?
Thanks.
Cheers
Gong-Bo Zhao
Has anyone test the accuracy of post-process? If some of the parameter space is not sampled by the original run but allowed by the latter constraint (pointed out by Hiranya Peiris), is the result still correct?
For example, are the following two results both correct?
I) Run MCMC with CMB+LSS+SN to generate *.data and then post process to give constrains of CMB+SN.
II) Run MCMC with CMB+SN to generate *.data and then post process to give constrains of CMB+SN+LSS.
I guess II) should be more accurate.
Am I right?
Thanks.
Cheers
Gong-Bo Zhao
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- Posts: 1943
- Joined: September 23 2004
- Affiliation: University of Sussex
- Contact:
Re: CosmoMC: Accuracy of post-process
Post-processing is importance sampling. So the distributions need to be similar, or the new one a subset of the old. Hence only II is likely to be good (as long as the extra constraint doesn't shrink the parameter space volume too much).
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- Posts: 73
- Joined: January 04 2005
- Affiliation: NAOC
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CosmoMC: Accuracy of post-process
Hi,Antony,
So you mean it is better to use the least dataset to generate *.data. Importance sampling does a better job to "add" dataset rather than "substract". Am I Right?
Thanks again.
Best,
Gong-Bo Zhao
So you mean it is better to use the least dataset to generate *.data. Importance sampling does a better job to "add" dataset rather than "substract". Am I Right?
Thanks again.
Best,
Gong-Bo Zhao
-
- Posts: 1943
- Joined: September 23 2004
- Affiliation: University of Sussex
- Contact:
Re: CosmoMC: Accuracy of post-process
Yes, though the less data you use originally the worse the importance sampling will be (less distribution overlap).
Of course if the datasets are not consistent (overlapping well) then it won't work at all. This is usually obvious by looking at the 1D plots.
Of course if the datasets are not consistent (overlapping well) then it won't work at all. This is usually obvious by looking at the 1D plots.