Oh, the text 2^(-3/2) is the most compact for the documentation, and it separates it from the 1/nu_cpmg part. So I'd prefer to present it that way for compactness and cleanliness. That can also allow us to pre-calculate it when the target function is initialised and and send the value of 0.35355339059327373 into the function instead. That would remove one exponential operation, again squeezing out a little speed. As nu_CPMG is fixed, even faster would be to pre-calculate an array of 2**(-3/2) / nu_CPMG and sent that in instead. That would really be the maximal optimisation for this part!
Cheers, Edward On 3 May 2014 13:45, Edward d'Auvergne <[email protected]> wrote: > Hi, > > The origin of this was exactly what Andy Baldwin said at > http://thread.gmane.org/gmane.science.nmr.relax.devel/5410/focus=5448 > - that there are many different tau_CPMG definitions and there is an > error in one of the equations in the original paper. The code in > relax is however correct. The eta_scale value should be > 0.35355339059327373. Feel free to fix the equations in the > documentation of the wiki, manual and lib.dispersion.cr72 docstring. > I wrote these before the code was fully tested and hence there is now > a mismatch. As for using 2.0**(-3.0/2.0) in the code, this is for the > fastest operation, avoiding the square root. But now that I look at > it, one mathematical operation can be dropped for speed and the factor > changed to 2.0**(-1.5). > > Cheers, > > Edward > > > On 3 May 2014 12:28, Troels Emtekær Linnet <[email protected]> wrote: >> Dear Edward. >> >> I was inspecting the code of model CR72. >> >> http://svn.gna.org/viewcvs/*checkout*/relax/trunk/lib/dispersion/cr72.py?revision=HEAD >> >> This is calculated as: >> >> eta_scale = 2.0**(-3.0/2.0) = 0.35 >> which is: 1 / sqrt(2**3). >> >> This differs from the definition in: >> http://wiki.nmr-relax.com/CR72_full#Equation >> http://www.nmr-relax.com/manual/full_CR72_2_site_CPMG_model.html >> http://www.nmr-relax.com/api/3.1/lib.dispersion.cr72-module.html >> >> where: >> eta_scale = 2.0**(2/3) = 1.58 >> which is {3}sqrt(2**2). >> >> If I compare to: >> http://wiki.nmr-relax.com/B14#Equation_compared_to_Carver_Richards_72 >> (DOI: 10.1016/j.jmr.2014.02.023 , eq 70,) >> >> And to, (DOI: 10.1016/S0076-6879(01)39315-1 , eq 25, with the twist >> that "tcp_Pa is the delay between 180 pulses in the CPMG pulse train", >> "delay/180/delay/delay/180/delay " so that tcp_Pa = 2xdelay >> >> Then really the manual should use: >> eta_scale = 2.0**(-3/2) >> or >> 1 / 2 sqrt(2) >> >> _______________________________________________ >> relax (http://www.nmr-relax.com) >> >> This is the relax-devel mailing list >> [email protected] >> >> 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 _______________________________________________ relax (http://www.nmr-relax.com) This is the relax-devel mailing list [email protected] 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
