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: spm_kl_dirichlet.m
    path of file: ./repos/bspm/thirdparty/spm12
    
    the code of the file until where you have to start completion: function [d] = spm_kl_dirichlet (lambda_q,lambda_p,log_tilde_pi)
% KL divergence between two Dirichlet densities
% FORMAT [d] = spm_kl_dirichlet (lambda_q,lambda_p,log_tilde_pi)
%
% Calculate KL (Q||P) = <log Q/P> where avg is wrt Q
% between two Dirichlet densities Q and P
%
% lambda_q      Parameter vector of first density
% lambda_p      Parameter vectpr of second density
% log_tilde_pi  <log (pi)> where avg is over Q. If this argument
%               isn't passed the routine will calculate it
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Will Penny 
% $Id: spm_kl_dirichlet.m 2696 2009-02-05 20:29:48Z guillaume $


    
function [d] = spm_kl_dirichlet (lambda_q,lambda_p,log_tilde_pi)
% KL divergence between two Dirichlet densities
% FORMAT [d] = spm_kl_dirichlet (lambda_q,lambda_p,log_tilde_pi)
%
% Calculate KL (Q||P) = <log Q/P> where avg is wrt Q
% between two Dirichlet densities Q and P
%
% lambda_q      Parameter vector of first density
% lambda_p      Parameter vectpr of second density
% log_tilde_pi  <log (pi)> where avg is over Q. If this argument
%               isn't passed the routine will calculate it
%___________________________________________________________________________
% Copyright (C) 2008 Wellcome Trust Centre for Neuroimaging

% Will Penny 
% $Id: spm_kl_dirichlet.m 2696 2009-02-05 20:29:48Z guillaume $

if nargin < 3
 m=length(lambda_q);
 lambda_tot=sum(lambda_q);
 dglt=psi(lambda_tot);
 for s=1:m,
   log_tilde_pi(s)=psi(lambda_q(s))-dglt;
 end