mie_ab.m

来自「MieMatlabMaetzler.zip 非常全功能的Mie散射程序 ma」· M 代码 · 共 34 行

function result = Mie_ab(m,x)

% Computes a matrix of Mie Coefficients, an, bn, 
% of orders n=1 to nmax, for given complex refractive-index
% ratio m=m'+im" and size parameter x=k0*a where k0= wave number in ambient 
% medium for spheres of radius a;
% Eq. (4.88) of Bohren and Huffman (1983), BEWI:TDD122
% using the recurrence relation (4.89) for Dn on p. 127 and 
% starting conditions as described in Appendix A.
% C. M鋞zler, July 2002

z=m.*x;
nmax=round(2+x+4*x.^(1/3));
nmx=round(max(nmax,abs(z))+16);
n=(1:nmax); nu = (n+0.5); 

sx=sqrt(0.5*pi*x);
px=sx.*besselj(nu,x);
p1x=[sin(x), px(1:nmax-1)];
chx=-sx.*bessely(nu,x);
ch1x=[cos(x), chx(1:nmax-1)];
gsx=px-i*chx; gs1x=p1x-i*ch1x;
dnx(nmx)=0+0i;
for j=nmx:-1:2      % Computation of Dn(z) according to (4.89) of B+H (1983)
    dnx(j-1)=j./z-1/(dnx(j)+j./z);
end;
dn=dnx(n);          % Dn(z), n=1 to nmax
da=dn./m+n./x; 
db=m.*dn+n./x;

an=(da.*px-p1x)./(da.*gsx-gs1x);
bn=(db.*px-p1x)./(db.*gsx-gs1x);

result=[an; bn];