You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: sphdiffusionslab.m
    path of file: ./repos/mmc/matlab
    
    the code of the file until where you have to start completion: function [res, xi, yi, zi] = sphdiffusionslab(Reff1, Reff2, h, xrange, yrange, zrange, cfg)
%
% [res,xi,yi,zi]= sphdiffusionslab(Reff,h,xrange,yrange,zrange,cfg)
%
% diffusion solution for a sphere inside an infinite homogeneous slab

    
function [res, xi, yi, zi] = sphdiffusionslab(Reff1, Reff2, h, xrange, yrange, zrange, cfg)
%
% [res,xi,yi,zi]= sphdiffusionslab(Reff,h,xrange,yrange,zrange,cfg)
%
% diffusion solution for a sphere inside an infinite homogeneous slab
%
% author: Qianqian Fang (q.fang <at> neu.edu)
%
% input:
%     Reff:  the effective reflection coeff.
%     xrange,yrange,zrange: a vector from where a grid will be created
%                   and the phi values will be calculated
%     h: the height of the slab
%     cfg: domain structure for internal/external parameters
%          cfg.v: speed of light in vacuum (mm/s)
%          cfg.a: sphere radius (mm)
%          cfg.omua: background (outside) mua (1/mm)
%          cfg.omusp: background (outside) mus' (1/mm)
%          cfg.imua: sphere (inside) mua (1/mm)
%          cfg.imusp: sphere (inside) mus' (1/mm)
%          cfg.src: spherical source position (R,theta,phi) R in mm
%          cfg.maxl: maximum serial expansion terms
%          cfg.omega: DPDW modulation frequency
%
% output:
%     res:  the output fluence for both the interior and exterior
%     regions
%
% example:
%   [phi_ana,xa,ya,za]=sphdiffusionslab(0,0,60,-30:0.8:30,0,-30:0.8:30);
%   contourf(xa,za,log10(abs(phi_ana)),40)
%
% this file is part of Mesh-based Monte Carlo (MMC)
%
% License: GPLv3, see http://mcx.sf.net/mmc/ for details
%

if (nargin < 7)
    cfg.v = 299792458000;  % mm/s
    cfg.a = 10;            % radius, mm
    cfg.omua = 0.002;      % outside mua 1/mm
    cfg.omusp = 0.990;     % outside mus' 1/mm
    cfg.imua = 0.050;
    cfg.imusp = 0.500;
    %   cfg.imua=0.002;
    %   cfg.imusp=0.990;
    cfg.src = [30, pi, 0];
    cfg.maxl = 20;
    cfg.omega = 0;
end