Update ar_fit.m

    coef = invR * Q'*yy(lstValid);

    res = yy(lstValid) - X(lstValid,:)*coef;

else

    [coef, res] = stepwise(X(lstValid,:), yy(lstValid));

    [B,SE,PVAL,in,stats,nextstep,history] = stepwisefit(X(lstValid,:), yy(lstValid),'Display','off');

    coef = B;

    res = stats.yr; 

%     [coef, res] = stepwisefit(X(lstValid,:), yy(lstValid));

end

res = res(1:n);

yhat = y - res;