s=3;
N=100;
X=rand(N,s);
a=1000*rand(s,1)
Z=rand(N,1);
Y=X*a+Z;
aSzk=(X'*X)^-1*X'*Y

clear all;
close all;

Err=1:10;
L=10;
s=3;
N=100;
for i=1:L
    X=rand(N,s);
    a=1000*rand(s,1)
    Z=rand(N,1);
    Y=X*a+Z;
    aSzk=(X'*X)^-1*X'*Y
    b=a-aSzk
    Err(i)=sum(b)
end

plot3(L,N,1/L*Err, '*')
grid on