function nthpoly(n,datafile)
% computes the fit parameter to nth polynomial
% using least square method
    i=1:n;
    data=load(datafile);
    X=data(:,1);
    Y=data(:,2);
    EY=data(:,3);
    np=length(X);
    A=zeros(np,n+1);
    for j=0:n
        A(:,j+1)=X .^ j;
    end
    V=diag(EY .^ 2);
    covariance=inv(A'*inv(V)*A);
    params=covariance*(A'*inv(V))*Y;
    disp('');
    fprintf("parameters:\n");
    disp(params);
    disp('');
   fprintf("covariance matrix:\n");
    disp(covariance);
    sigma2=diag(covariance)';
   sigma= sqrt(sigma2);
    sigij=sigma'*sigma;
    disp('');
    correlation= covariance ./ sigij;
    disp('correlation:');
    disp(correlation);
end