[Ifeffit] Mathematical expressions for the path parameters in Fitting

[sumitk at barc.gov.in]

Hello,
In EXAFS data modeling carried out by fitting excercise, we develop
mathematical expressions for  different path parametrs as functions of a
smaller set of fitting parameters that can be adjusted to achieve to best
fit to the data. I am carrying out EXAFS analysis of Eu(III) sorbed on
different environmentally relevent mineral oxides. In conection of this i
also analysed some reference standard compounds. In developing expression
for different path parameters, though i developed the expressions using my
own  understanding and taking help from one of Shelly's tutorial regarding
SnO2 case, i am not confident. Basically SS2, and deltaE expressions
puzzle me.
Could someone help me in understanding basic approach in developing their
expressions(for reference Eu2O3 structure could be taken).
Regards,
Sumit