Warn for possibility of 3-state exchange if fit is too poor (χ2 is too high)

Issue: some NMR probes undergo exchange between 3 states, but GUARDD only fits 
to the 2-state exchange model, and the user should not be misled to the 
erroneous assumption that 2-state exchange is the only reasonable explanation.

Solution 1
Warn for 3 site exchange if χ2 is too high (not sure how high is too high 
though)

Solution 2
Fit 3-state exchange (very difficult to program into GUARDD, due to the data 
structures which are currently implemented).

Reference for study on 3-state exchange
Neudecker, P., Korzhnev, D. M. & Kay, L.E. (2006). Assessment of the effects of 
increased relaxation dispersion data on the extraction of 3-site exchange 
parameters characterizing the unfolding of an SH3 domain. Journal of 
Biomolecular NMR, 34, 129-35. http://view.ncbi.nlm.nih.gov/pubmed/16604422

Original issue reported on code.google.com by ian.klec...@gmail.com on 11 Sep 2011 at 10:12

rachitshah86 / guardd

Warn for possibility of 3-state exchange if fit is too poor (χ2 is too high) #18