On Tue, Mar 10, 2009 at 6:23 PM, Sébastien Morin
<[email protected]> 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
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