/* Single Exponential Smoothing */
/* (n periods ahead: flat) */
new; cls;
let data[12,1]=
23
25
36
31
26
28
48
36
31
42
53
43
;
nahead=4;
t=seqa(1,1,rows(data)+nahead);

library pgraph;
graphset;
_pltype=6;
_plegctl=1;
_plegstr="actual\000predicted\000n ahead";
title("Single Exponential");
alpha=0.5;
xy(t,(data|miss(zeros(nahead,1),0))~sesf(data,alpha,nahead));




proc sesf(x,alpha,nahead);
   local n,m,mp,i;
   n=rows(x);
   m=zeros(n,1);
   m[1]=x[1];
   i=2;
   do while i<=n;
      m[i]=alpha*x[i-1]+(1-alpha)*m[i-1]; 
      i=i+1;
   endo;
   mp=miss(zeros(n-1,1),0)|m[n]*ones(nahead+1,1);
   m=m|miss(zeros(nahead,1),0);
   retp(m~mp);
endp;