Newmark's Method for Linear Systems

Hi all,

Hope someone will explain to me about this file exchange's code(Dr.Siva-Newmark's Method for Linear Systems-http://www.mathworks.com/matlabcentral/fileexchange/32143-newmark-s-method-for-linear-systems/content/Newmark's%20Method%20for%20Linear%20systems/NewmarkMethod.m). The question are:-

1)Why n=length (M).n is for?I am not really expert in loop or cycle coding?

 % Time step
ti = 0. ;
tf = 4. ;
dt = 0.1 ;
t = ti:dt:tf ;
nt = fix((tf-ti)/dt) ;
n = length(M) ;
depl = zeros(n,nt) ;
vel = zeros(n,nt) ;
accl = zeros(n,nt) ;
U = zeros(sdof,nt) ;

2)What is the different between depl-modal displacement's and U-system's displacement?