On Tue, Mar 10, 2009 at 6:23 PM, Sébastien Morin
<sebastien.morin.1@xxxxxxxxx> wrote:
Hi Ed,
PY is next to me and we discussed this issue together.
This seems very strange since values of the AICc criterion (extracted
during model selection) are not equal for models with or without these
10e-19 Rex... If this is in s-1, then the criterion should be almost
equal as a Rex of 10e-19 s-1 would be negligible.
For this value, see below. If Rex really is zero between 2 nested
models where the Rex parameter is the only difference, the AIC values
should be different by 2! The reason is because as:
AIC = chi^2 + 2k,
if Rex = 0, then the other parameters must be the same (unless of a
model or optimisation failure) and the chi-squared values equal.
Hence as the parameter number difference k_diff = 1, then AIC_diff =
2.
Moreover, if using the latex_mf_table.py script, the Rex values are
reported and associated to the 800 MHz field strength with values in s-1
between 1 and 6... These values correspond to those we would obtain by
multiplying the Rex values in the xml results file by (2 pi frq)**2...
Hence, I would think values extracted in the xml file, that is values
one gets with the command "value.display('Rex')", are in the field
independent format obtained from Rex/omega**2.
Are we wrong ?
I just checked the code in the math_fns package, and the chemical
exchange is handled internally as Rex/omega**2. Looking at the XML
dumping code, this just dumps the contents of the spin container
directly to file, hence the value is Rex/omega**2. Therefore the
comment in the XML results file is incorrect. Would you be able to
file a bug report for this? Then the fixes can be tracked. It would
be better to have two reports, one for the latex_mf_table.py script
and one for the XML results file.
Cheers,
Edward
Re: Rex value