[COSMOMC] : sigma_8

[Pierre Delsart]

Hello,
I just try to test my module in cosmomc without CMB, mpk and SN, just my module. I need sigma_8 free, thus I put : get_sigma8 = T in params.ini.
I launch a chain with 10 000 samples but the values of sigma8 are not that I expected.
I know that the value of -ln(L) is responsible of the move of the differents parameters. But in my case, I get the impression that the move of sigma8 don't depend on my value of -ln(L).
Could you explain me how operate sigma8 please?
Thanks a lot

[Antony Lewis]

sigma_8 is a derived parameter, but if get_sigma8 = T it should be written out correctly in the chain files.