Hi,
not sure, if I understood correctly, but does this what you need?
% some data
x = 1:10;
% n = 2 or 3 or ...
n = 2;
% build the difference ...
dx = x(n+1:end) - x(1:end-n)
This would work for vectors only, but generalization to matrices is of course straigt forward ...
Titus