用 O(h^2) 阶的有限差分方法求区间[a ， b] 上的边值问题 x =p(t)*x (t)+q(t)*x(t)+r(t),x(a)=alpha,x(b)=beta 的逼近。 并附上三阶、四阶、五阶 Rungkuta 法（附件里面）-The boundary value problem of x　=p (b])*x (T)+q (T)*x (T) () (T) (T)+r () x (), =alpha (a) () =beta, X (b) O () () [a () (h^2), is obtained by the finite difference method. And attach the three order, four order, five order Rungkuta method (Annex inside)