PweFarField

 Calculates far-field properties (scattered field only) for PWE.

 Parameters:
 - stM:    structure with results of the Mie computation
           can be obtained by calling PweSolveSingleSphere
           of MulPweSolveMultiSphere with sCoeff='coeff'
 - nNbTheta: integer scalar
             number of theta points used for computations
 - stPinTaun: structure (optional)
              with functions of theta pi_n and tau_n
              if omitted, then the functions are computed from scrath
              it is faster to pass this structure as argument if these
              functions have already been calculated 
 
 Returns: structure stEfarSca with fields
 stEfarSca.x: [L x 1]
 stEfarSca.theta: [1 x T]
 stEfarSca.lambda: [L x 1]
 stEfarSca.S1: [L x T] S1 scattering amplitudes (see supplementary
               information)
 stEfarSca.S2: [L x T] S2 scattering amplitudes (see supplementary
               information)
 stEfarSca.Qsca: [L x 1] scattering coefficients computed from integrals
                 over theta. Should be the same as obtained from PweQcoeff
                 for consistency

 This file is part of the SPlaC v1.0 package (copyright 2008)
 Check the README file for further information

0001 % get theta dependence if not provided
0002 if nargin < 3
0003     theta=linspace(0,pi,nNbTheta); % row [1 x T]
0004     stPinTaun=PwePinTaun(stM.nNmax,transpose(theta)); % fields are [T x nNmax]
0005 end
0006 
0007 % stM already contains fields cn1 and dn1
0008 stEsurf=PweEsurf(stM.lambda,stM.epsilonM,stM,Inf,nNbTheta,'scattering',stPinTaun);
0009 
0010 stEfarSca.x=stM.x;
0011 stEfarSca.theta=stEsurf.theta;
0012 stEfarSca.lambda=stEsurf.lambda;
0013 stEfarSca.S1=-stEsurf.Esf;
0014 stEfarSca.S2=stEsurf.Ect;
0015 stEfarSca.Qsca=4*stEsurf.MLocParaAve./(stM.x).^2; % check Qsca from far-field average
0016 
0017