Hi,
Unfortunately, there is no ability to fix one of the model-free
parameters during optimisation in relax yet. This is something that
has been requested one or two times over the years. This is
complicated as the gradients and Hessians (first and second partial
derivates) need to be modified with this in mind, as the curvature of
the space changes. The fixed parameter is not part of the gradient or
Hessian, and has to be removed. This really complicates the target
function, gradient, and Hessian and, due to the low demand, has not
been implemented.
Are you able to optimise this parameter and see if you get 0.111? And
are you able to extract the timescale of this process (the methyl
group rotamer jumps)? From memory, someone has optimsed these models
using a grid search. This coarse optimisation can be performed in
relax as you are able to specify the fine details of the grid search.
It is slower, but will do the job. You could even implement a zooming
grid search if your scripting skills are up to it to be able to
relatively quickly find the parameters to high precision. Anyway, I
hope this info helps.
Regards,
Edward
On 6 April 2011 17:39, Tiago Pais <tpais@xxxxxxxxxxx> wrote:
Hi,
I would like to make an analysis of side-chain relaxation data with the S2f
parameter (in model 5) set to 0.111.
Is it possible to do this with RELAX? How?
Thanks in advance.
Cheers
Tiago P
**************************************
Tiago Pais, PhD. student
Cell Physiology & NMR
Instituto de Tecnologia Química e Biológica-Oeiras
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Re: How to set S2f to 0.111?