A=rkp(vec,k)

function A=rkp(vec,k)
% -----------------------------------------------------------------
% Elaborated by : BEN HASSEN Anis 
% "Institut Suprieur de Gestion de Tunis" (ISG Tunis)
% University of Tunis
% 41, rue de la Libert - Cit Bouchoucha - C.P. : 2000 Le Bardo
% Tunisia
% University e-mail: http://www.isg.rnu.tn/
% Personal e-mail: [e-mail]
% _________________________________________________________________
% January 14, 2004.
% auxiliary function....

T=length(vec);
i=1:T-k+1;
M=zeros(T-k+1,k);
for j=1:k,
    M(:,j)=i+j-1;
end
A=sum(vec(M'));