for x = u
        %x = 1:1:length(u);
        i = length(a):-1:1;
        upper = (a.*(x.^i))./i;
    end
    for x = u
        %x = 1:1:length(u);
        i = length(a):-1:1;
        lower = (a.*(x.^i))./i;
    end
        y = upper-lower;