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[sqw_Ei,sphiw]=Sqw_dynamic_range(s,Ei): crop the S(|q|,w) to the available dynamic range


function [s, sphi] = Sqw_dynamic_range(s, Ei, angles, options)


 [sqw_Ei,sphiw]=Sqw_dynamic_range(s,Ei): crop the S(|q|,w) to the available dynamic range
   for given incident neutron energy.

  The S(q,w) is a dynamic structure factor aka scattering function.

 The dynamic range is defined from the momwntum and energy conservation laws:
  Ef         = Ei - w                                is positive
  cos(theta) = (Ki.^2 + Kf.^2 - q.^2) ./ (2*Ki.*Kf)  is within [-1:1]

 The incident neutron energy can be computed using:
  Ei = 2.0721*Ki^2 = 81.8042/lambda^2 with Ki in [Angs-1] and lambda in [Angs]

 omega = Ei-Ef = energy lost by the neutron
    omega > 0, neutron looses energy, can not be higher than Ei (Stokes)
    omega < 0, neutron gains energy, anti-Stokes

 The scattering angle phi can be restricted to match a detection area
 with the syntax:
   sqw_Ei=Sqw_dynamic_range(s, Ei, [angles])

 The syntax:
   [sqw_Ei, sphiw] = Sqw_dynamic_range(s,...)
 also returns the S(phi,w) data set, which shows the detected signal vs scattering 
 angle and energy transfer.

   s:  Sqw data set, e.g. 2D data set with w as 1st axis (rows, meV), q as 2nd axis (Angs-1).
   Ei: incoming neutron energy [meV]
   angles: detection range in [deg] as a vector. Min and Max values are used.
   sqw:   S(q,w)   cropped to dynamic range for incident energy Ei.
   sphiw: S(phi,w) angular dynamic structure factor for incident energy Ei.

 Example: Sqw_dynamic_range(s, 14.8, [-20 135])

 See also: Sqw_Bosify, Sqw_deBosify, Sqw_symmetrize, Sqw_scatt_xs
 (c) E.Farhi, ILL. License: EUPL.


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