function [r,xtilde]=dpcm(x,a)% Usage: [r,xtilde]=dpcm(x,a)% Differential Pulse Coded Modulation% x: input source vector to be encoded% a: prediction filter% r: residue vector quantized to integer%%    r(t) = Q[x(t)-xhat(t)] = Q[x(t)- sum a(i)xtilde(t-i)]%    xtilde(t) = xhat(t) + r(t)%% copyright (c) 1997 by Yu Hen Hu% created: 11/24/97%[m,nx]=size(x);  if min(m,nx) > 1, error('x must be a vector'); break, endif m==1 & nx > 1, x = x'; m=nx;  end  % ensure x is a column vector[p,na]=size(a);if p==1 & na > 1, a = a'; p=na;  end  % ensure a is a col. vector% First p element of x must be sent unchanged as part of r after% scaler quantizationr=round(x(1:p)); xtilde=r;for t=p+1:m,   xhat(t)=a'*xtilde(t-1:-1:t-p);   r(t)=round(x(t)-xhat(t));   xtilde(t)=xhat(t)+r(t);end