URL:
<http://gna.org/bugs/?22210>
Summary: The 'LM63 3-site' relaxation dispersion model does
not work.
Project: relax
Submitted by: bugman
Submitted on: Tue 17 Jun 2014 12:01:08 PM UTC
Category: relax's source code
Specific analysis category: Relaxation dispersion
Priority: 5 - Normal
Severity: 4 - Important
Status: None
Assigned to: bugman
Originator Name:
Originator Email:
Open/Closed: Open
Release: 3.2.2
Discussion Lock: Any
Operating System: All systems
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Details:
The Luz and Meiboom 1963 3-site 'LM63 3-site' relaxation dispersion CPMG model
(http://wiki.nmr-relax.com/LM63_3-site) is buggy. This can be seen in the
source code directly:
http://www.nmr-relax.com/api/3.1/lib.dispersion.lm63_3site-pysrc.html
The formula is:
_3_
\ phi_ex_i / 4 * nu_cpmg / ki \ \
R2eff = R20 + > -------- * | 1 - ----------- * tanh | ----------- | |
.
/__ ki \ ki \ 4 * nu_cpmg / /
i=2
But the code implementing the tanh(ki/(4*nu_cpmg)) is:
back_calc[i] += rex_B * (1.0 - cpmg_frqs[i] * tanh(quart_kB *
cpmg_frqs[i]) / quart_kB)
Clearly the multiplication in the tanh function must be a division!
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