function epred = implicit_obj(ab,x,ye)a = ab(1);b = ab(2);n = length(ye);epred = zeros(1,n);estart = .1;for i = 1:n  fun = @(ei) (ye(i)-ei - a*((ye(i)-ei) - b*x(i)).^2);  epred(i) = fzero(fun,estart);end