Sqw = Sqw_Sab(Sqw, M, T)
Sqw_Sab: convert an S(alpha,beta) into a 2D S(q,w).
The S(alpha,beta) is a representation of the dynamic structure factor
using unitless momentum and energy variables defined as:
alpha= h2q2/2MkT = (Ei+Ef-2*mu*sqrt(Ei*Ef))/AkT
beta = -hw/kT = (Ef-Ei)/kT
A = M/m
mu = cos(theta) = (Ki.^2 + Kf.^2 - q.^2) ./ (2*Ki.*Kf)
input:
s: S(alpha,beta) data set e.g. 2D data set with alpha as 1st axis (rows), beta as 2nd axis.
M: molar weight of the atom/molecule in [g/mol].
when omitted or empty, it is searched as 'weight' or 'mass' is the object.
T: when given, Temperature to use. When not given or empty, the Temperature
is searched in the object. The temperature is in [K]. 1 meV=11.605 K.
output:
Sqw: S(q,w) 2D data set, classical/symmetric (iData)
conventions:
w = omega = Ei-Ef = energy lost by the neutron [meV]
omega > 0, neutron looses energy, can not be higher than Ei (Stokes)
omega < 0, neutron gains energy, anti-Stokes
references: M. Mattes and J. Keinert, IAEA INDC(NDS)-0470, 2005.
R. E. MacFarlane, LA-12639-MS (ENDF-356), 1994.
Example: Sqw = iData( fullfile(ifitpath,'Data','SQW_coh_lGe.nc') );
Sab = Sqw_Sab(Sqw,72.6,300);
plot(log(Sab)
(c) E.Farhi, ILL. License: EUPL.