Re: Reference for the Skrynnikov derivation?Re: Reference for the Skrynnikov derivation?Hi Edward, I agree.However, in practice the assumption that R2A=R2B is one that I use always. Fitting two R2 for the two states is close to impossible, unless the data are really outstanding. Having the two different R2 in the matrices is nice from an intellectual and eductational point of view, but otherwise not of practical relevance. Likewise, all the things with R1 are practically not useful, as we anywas assume that longitudinal relaxation does not have any impact on the dispersions. Again, fitting the R1's is very difficult, and in practice not relevant. So, as you suggested in a previous message, you can ignore non-180deg pulses, ignore R2 differences between the states, and ignore R1.
paul Quoting Edward d'Auvergne <edward@xxxxxxxxxxxxx>:
Hi, There does appear to be one difference. It looks like this model uses the assumption that R20A = R20B = R20 (or in the original notation, R2G = R2E = R2). The R1G, R1E, and R2E values are not used in the code. So I assume that it should give the same result as the reduced models as I have now created in relax from the fitting_main_kex.py code rather than the full R20A != R20B models. So if the spin-spin relaxation rates for the two states are significantly different, then this model should not be able to reproduce the results of the other models in fitting_main_kex.py. Though maybe I have missed something? Cheers, Edward On 17 July 2013 15:35, Paul Schanda <paul.schanda@xxxxxx> wrote:Hi Edward, No, there is nothing published. Nikolai said that anyways it's trivial :-) He derived it basically by putting the Bloch-McConnell equations to Maple and simplifying it there. I guess there is something like a FullSimplify (that's Mathematica-style, but I guess Maple does it similarly). I guess the main advantage is speed, and in fact in all cases I have seen it does exactly the same as the explicit Bloch-McConnell treatment, so I see it as the treatment that one would like to use. I agree that having something undocumented there is not particularly nice, but in the end it's up to the user whether or not to use this faster treatment (and compare it to the slower Bloch-McConnell one if needed). paul On 17.07.13 15:14, Edward d'Auvergne wrote:Hello, I am now adding the numerical dispersion model derived by Nikolai Skrynnikov to relax. This is model 5 from the fitting_main_kex.py script (for reference attached to https://gna.org/task/?7712). I was wondering if there was a published reference for this that you know of? This would be useful for the model name and for the documentation. Cheers, Edward-- Paul Schanda, Ph.D. Biomolecular NMR group Institut de Biologie Structurale Jean-Pierre Ebel (IBS) 41, rue Jules Horowitz F-38027 Grenoble France +33 438 78 95 55 paul.schanda@xxxxxx http://www.ibs.fr/groups/biomolecular-nmr-spectroscopy?lang=en