COSMOMC - some chains do not progress at all.

Use of Cobaya. camb, CLASS, cosmomc, compilers, etc.
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Teeraparb Chantavat2
Posts: 8
Joined: May 03 2021
Affiliation: Naresuan University

COSMOMC - some chains do not progress at all.

Post by Teeraparb Chantavat2 » May 07 2022

Dear All,

I have been running CosmoMC with five chains for the same dataset for 4 days. I noticed that two of five chains last modification date was just on the first day while the other three get updated occasionally. However, one of the chains seems to progress must faster than the rest. Just to make sure you understand what I am talking about I will give you the number of steps for each chain:

chain 0 - 182
chain 1 - 207
chain 2 - 46786
chain 3 - 29340
chain 4 - 20480

Runtime 4 days 1 hour approx.

My questions are:
1) This is kind of chain progression normal?
2) If this is not normal, should I stop and rerun the chain again, possibly with some snapshot? How do I fix this in the ini file.

Best,

Antony Lewis
Posts: 1775
Joined: September 23 2004
Affiliation: University of Sussex
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Re: COSMOMC - some chains do not progress at all.

Post by Antony Lewis » May 09 2022

It is not normal, you can usually tell if chains are running OK within a couple of hours (and stop if not). You can certainly generate a covmat from that run and re-start. Check your propose and start ranges for each parameter.

Teeraparb Chantavat2
Posts: 8
Joined: May 03 2021
Affiliation: Naresuan University

Re: COSMOMC - some chains do not progress at all.

Post by Teeraparb Chantavat2 » May 16 2022

Thank Anthony,

I have checked it. There is nothing wrong with the parameter range and the initialization file. It is more to do with the server itself - probably with the MPI setting on the server. I run the same initialization file on another machine and it work fine.

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