Ah, for this problem, have a look at the math.atan2() function ;) I
have tried to avoid math.atan() as much as possible within relax, well
where sign is important:
$ grep -r atan . --exclude-dir=.svn
Hmmm, I can see that it is used in a few of the lib.dispersion
modules! I might have to fix this for relax 3.1.8 (if you haven't
seen the latest commit messages, relax 3.1.7 is in the process of
being released).
Cheers,
Edward
On 14 March 2014 15:58, Troels Emtekær Linnet <tlinnet@xxxxxxxxxxxxx> wrote:
Dear Edward.
I have wondered about the outcome of the theta values.
In the systemtest:
Relax_disp.test_value_write_calc_rotating_frame_params_auto_analysis
I have hardcoded the values of an output of theta values.
But many of them are negative.
If we take the article of:
3. Palmer, A.G. & Massi, F. (2006). Characterization of the
dynamics of biomacromolecules using rotating-frame spin relaxation NMR
spectroscopy. Chem. Rev. 106, 1700-1719 http://dx.doi.org/10.1021/cr04042875
And look at Figure 1.
We see that
tan(theta) = w_1 / Omega
If w_1 (Spin-lock offset) is always positive, but Omega can be
negative, then negative values
are to be expected for w_1 / Omega.
For the symmetry of atan, theta_calc = atan(-x) = - atan(x), the theta
angle describing the tilted rotating frame relative to the laboratory
frame should then be
theta = pi + atan(-x) = pi - atan(x) = pi - abs(atan(x))
Best
Troels
2014-03-13 19:51 GMT+01:00 Edward d'Auvergne <edward@xxxxxxxxxxxxx>:
Hi,
This is the standard way of calculating theta. Note that some of the
dispersion models in lib.dispersion do not use this code and actually
calculate a different theta value using the population averaged
spin-lock offset.
Regards,
Edward
On 13 March 2014 19:44, Troels E. Linnet
<NO-REPLY.INVALID-ADDRESS@xxxxxxx> wrote:
Follow-up Comment #34, sr #3124 (project relax):
The theta calculation in relax is:
# Calculate the tilt angle.
omega1 = point * 2.0 * pi
Delta_omega = shifts[ei][si][mi] - offsets[ei][si][mi][oi]
Domega[ei][si][mi][oi].append(Delta_omega)
if Delta_omega == 0.0:
theta[ei][si][mi][oi].append(pi / 2.0)
else:
theta[ei][si][mi][oi].append(atan(omega1 / Delta_omega))
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Re: [sr #3124] Grace graphs production for R1rho analysis with R2_eff as function of Omega_eff