Hi Shelly, Scott,
I request that Athena reports the uncertainty in the basic EXAFS parameters and not just the fitted variables. For example, the uncertainty in the optimized debye temperature is reported, but the uncertainty in sigma2 value is not currently reported. I could see how this could be done by Athena or by including a new function in IFEFFIT.
While we're on the topic...
FEFFIT used to report the uncertainties in computed variables (what are now DEF's) in the feffit.prm file. As far as I've been able to tell, Artemis doesn't report that information anywhere, and I'm not clear if ifeffit still computes it. Is it in there somewhere, and am I just missing it? In any case, I would like it if uncertainties in def'd variables should be given everywhere that uncertainties in guessed variables are given.
Right now, Ifeffit does not do this estimation of uncertainties in any Path Parameters or "def"ined quantities. It would be possible to re-do what Feffit did for this, but I think it is slow enough that it wouldn't make sense to do this automatically for all Path Parameters and defined quantities for each fit. The approach used in Feffit calculated (by brute force) the derivative for each Parameter (either Path Parameter or defined value) P_i with respect to each fitting variable x_j and added the results in quadrature: delta_P_i = Sqrt(Sum_j,k dx_j * dx_k * dP/dx_j * dP/dx_k * Correl(x_j, x_k) ) Again, the derivatives dP_i/dx_j were calculated by brute force (change variable x_i to x_i +/- dx_i and see how the value of parameter P changes). It is worth questioning whether this approach is actually accurate enough, and whether it could be done better or faster. I would propose adding a command to do this for a specified defined parameter or path (in which case, it would generate the uncertainties for all Path Parameters). Obviously, This would take some time.... --Matt PS: as an aside for those of you who never used Feffit: Feffit is an older version of Ifeffit that _ONLY_ runs as a script in batch mode, can not do any graphics or interactive analysis, and is missing many of the features of Ifeffit. It does have the feature of being faster than Ifeffit for most fits, because it knows you won't be able to change the model and also optimizes how it does Fourier Transforms (because it knows you won't be looking at the fit as it is progressing). It did propogate uncertainties from variables to path parameters and defined quantities as above, but only had to do it once.