#include <stdio.h>
/* regre2.c : 1999 3 28 by T.Oguni */
#define N 10
regre2(a,x,y,n)
double a[2],x[N],y[N];
int n;
{
  double sumx,sumy,xx,xy,yy,nn,mx,my;
  int i;
  sumx=sumy=xx=xy=yy=0.0;
  nn=(double)n;
  for (i=0; i<n; i++){
    sumx+=x[i]; sumy+=y[i];
    xx+=x[i]*x[i]; xy+=x[i]*y[i]; yy+=y[i]*y[i];
  }
  mx=sumx/nn; my=sumy/nn;
  a[0]=(xy-nn*mx*my)/(xx-nn*mx*mx);
  a[1]=(my*xx-mx*xy)/(xx-nn*mx*mx);
  return;
}
/* main */
main(){
  double x[N]={1.,2.,3.,4.,5.,6.,7.,8.,9.,10.};
  double y[N]={1.,2.,3.,5.,7.,11.,13.,17.,19.,23.};
  double a[2],yhat[N];
  int i, n=10;
  regre2(a,x,y,n);
  printf("a= %f b=%f\n", a[0],a[1]);
  for (i=0; i<n; i++){
    yhat[i]=a[0]*x[i]+a[1]; }
  printf("Pbserved and estimated values.\n");
  for (i=0; i<n; i++){
    printf("%d %f %f %f\n", i+1, y[i],yhat[i],y[i]-yhat[i]); }
}