CosmoCoffee

[ruchika kaushik]

I have installed CosmoMC successfully in an 8 core Xeon processor
workstation. When I use the command mpirun -np 4 ./cosmomc test.ini , my
8 cores are high with num_thread = 0 & action=0. Could you please tell why
cosmomc is utilizing full cores and not 4 as given in command line. And if I
try to use -n p 8, it throws error, no that much slots are available


How many chains are recommended for good statistics?

[Antony Lewis]

num_thread =0 will automatically set the number of threads, in your case you have two threads per chain to use all the cores. You can set num_threads=1 if you really only want one per chain.

Should be no space in "-n p"?

I usually run four chains till R−1 ~ 0.02 or 0.01 (0.05 is usually fine if you don't want to make 2D plots).

[ruchika kaushik]

Thank you very much for the post. CosomoMC is working fine in this case.

My processor is Intel® Xeon(R) CPU E3−1271 v3 @ 3.60GHz × 8

Now for action = 0,
If I use mpirun -np 4 ./cosmomc test.in with num_threads = 1, it uses exactly four cores. And with num_threads = 2, it uses 8 cores. So its fine here.

But. If I use mpirun -np 8 with num_threads=1, it gives this following error

[Antony Lewis]

That looks like an mpirun error, nothing to do with Cosmomc. Maybe other programs on your computer are using too much cpu to assing all to cosmomc (or maybe it's seeing the physical cores rather than hyperthreaded).

[ruchika kaushik]

Thank you. It is a hyperthreaded processor.

[Shouvik Roychoudhury]

Keep num_threads=0. It should work.