function ltr=rbgetltr(cfg,wavelength)
%
% ltr=rbgetltr(cfg,wavelength)
%
% Compute the transport mean free path (l_tr=1/mu_tr) in mm in a medium 
% where mu_tr=mua+musp is the transport coefficient, mua is the absorption 
% coeff and musp=mus*(1-g) is the reduced scattering coeff, mus is the 
% scattering coeff and g is the anisotropy
%
% author: Qianqian Fang (q.fang <at> neu.edu)
%
% input:
%     cfg: the forward simulation data structure
%     wavelength (optional): if cfg.prop is a containers.Map for
%          multispectral simulations, wavelength specifies which
%          wavelength, it can be a string or an integer.
%
% output:
%     ltr: transport mean free path in mm
%
% license:
%     GPL version 3, see LICENSE_GPLv3.txt files for details 
%
% -- this function is part of Redbird-m toolbox
%

bkprop=rbgetbulk(cfg);
if(isa(bkprop,'containers.Map'))
    if(nargin==1)
        wavelength=bkprop.keys;
        wavelength=wavelength{1};
    end
    bkprop=bkprop(wavelength);
end
ltr=1/(bkprop(1)+bkprop(2)*(1-bkprop(3)));

