Dmfit program - on line help pages
The "dmfit" program is is a versatile tool
designed for fitting NMR spectra, including solid state NMR. It
provides a variety of different models that account for :
-
Gaussian/Lorentzian lines,
- spinning
sidebands,
- Chemical Shift
Anisotropy (static and MAS),
- first and second
order Quadrupolar interaction (static and MAS)
- ...
Optimisation Algorithm :
The mismatch criterion that we use is a simple quadratic distance between the
experimental and modelled spectrum. This could of course be improved in some
cases but its advantage is to make no hypothesis upon the type of data that we
consider. The optimisation algorithm aims at minimizing the mismatch criterion
by varying the parameters of the different lines. As the computation of the
model includes non-linear dependencies to the different parameters and, in some
cases, no simple analytical form, we use an iterative algorithm. Starting with
an approximate solution we compute and add an increment to try to converge to a
local minimum. This does not ensure the unicity of the obtained solution that
will only be the closest to the starting point. The algorithm used in our
program is a constraint gradient protocol which involves computation of the
partial derivatives over each of the parameters for all variable parameters and
each point of the experimental spectrum. The resolution of the n-linear system
of equation yields an increment that is finally added to the starting parameter
set. This procedure is rather robust when close to a final well defined.
File format used by the program...