% mirror pading
%function [y]=pad(x, m)
function [y]=pad(x, m)
 n = length(x);
 p0 = x(1:m);
 pn = x(n-m+1:n);

 for k=1:m
   q0(k) = p0(m-k+1);
   qn(k) = pn(m-k+1);
 end

 y = [q0 x qn];