Hi, That looks interesting. I've CC'ed a few others who might also find this paper interesting. Though Andrew Baldwin's words are very strong - probably stronger than needed to justify the creation of a new dispersion model. Note that reference 37 is: Tollinger, M., Skrynnikov, N. R., Mulder, F. A., Forman-Kay, J. D. & Kay, L. E. Slow dynamics in folded and unfolded states of an SH3 domain. J Am Chem Soc 123, 11341-11352, (2001). This is what he is referring to with the text "As described in Supplementary Section 8, while exact, this algorithm can lead to significant errors...". This is the 'NS CPMG 2-site expanded' model used as the default numeric model in relax (http://wiki.nmr-relax.com/NS_CPMG_2-site_expanded) and the Maple code was donated by Martin Tollinger and Nikolai Shrynnikov. It was translated to Python code by Mathilde Lescanne, Paul Schanda, and Dominique Marion. I then reformatted it to fit into the relax library (http://www.nmr-relax.com/api/3.1/lib.dispersion.ns_cpmg_2site_expanded-module.html). Anyway, if this is really an exact analytic solution for all timescales and populations, and is numerically stable in the fast exchange regime, then this would be very useful. It obviously won't handle off-resonance effects like CATIA can, and which relax might in the future. But it would replace the LM63 (http://wiki.nmr-relax.com/LM63), CR72 (http://wiki.nmr-relax.com/CR72), IT99 (http://wiki.nmr-relax.com/IT99) and TSMFK01 (http://wiki.nmr-relax.com/TSMFK01) models. And it would give identical results to the numeric models, but would be orders of magnitude faster. It would be interesting to test against. Note those quotes you gave, if the previous is true then such statements are not necessary and are just aggressive hyperbole. What does "significant errors when evaluated at double floating point precision" even mean? There's no citation or figure demonstrating this, and this goes against what people would have seen in the field. I have not seen parameter errors that are not justified by the experimental errors. Anyway, an exact 2-site analytic solution for CPMG-type experiments for all situations requires no justification for its significance. Would you be interested in adding a new dispersion model to relax? If yes, then you know what to do - http://wiki.nmr-relax.com/Tutorial_for_adding_relaxation_dispersion_models_to_relax ;) Adding dispersion models to relax is a rather easy process, especially if you are already a developer. Going by the current naming in relax, it would have the name of 'B14'. It's a bit too late to include in the relax relaxation dispersion paper though (http://dx.doi.org/10.1093/bioinformatics/btu166). Regards, Edward On 22 April 2014 11:32, Troels Emtekær Linnet <tlinnet@xxxxxxxxxxxxx> wrote:
Hi Edward. An interesting paper I just found in the alerts. http://dx.doi.org/10.1016/j.jmr.2014.02.023 An exact solution for R2,eff in CPMG experiments in the case of two site chemical exchange By Andrew J. Baldwin Specifically these lines in the introduction took my attention: - http://wiki.nmr-relax.com/CR72 " When the population of the minor state exceeds approximately 1%, calculation errors that are larger than the experimental uncertainty can accumulate when the Carver-Richards equation is used (Figure 1), which can lead to errors in the extracted parameters." - http://wiki.nmr-relax.com/NS_CPMG_2-site_expanded "As described in Supplementary Section 8, while exact, this algorithm can lead to significant errors when evaluated at double floating point precision, as used by software such as MATLAB". "an exact solution for the effective transverse relaxation rate in a CPMG experiment, R2,eff, in the commonly encountered scenario of two-site exchange of in-phase magnetisation (Equation (50)) is derived. The result is expressed as a linear correction to the Carver Richards equation (summarised in Appendix 1), and algorithms based on this have significant advantages in both precision and speed over existing formulaic approaches." Best Troels _______________________________________________ relax (http://www.nmr-relax.com) This is the relax-devel mailing list relax-devel@xxxxxxx To unsubscribe from this list, get a password reminder, or change your subscription options, visit the list information page at https://mail.gna.org/listinfo/relax-devel