Ritz法解决-u +u=x 0<x<1，u(0)=0,u(1)=0的有限元边值问题。精确解为u(x)=1/(exp(1)-1/exp(1))*exp(-x)+1/(1/exp(1)-exp(1))*exp(x)+x，基函数为g(i)=sin(i*pi*x)-This matlab code is used to solve the boundary value problem of　the differential equation:

-u　+u=x 0<x<1，u(0)=0,u(1)=0, where the accurate solution is :

u(x)=1/(exp(1)-1/exp(1))*exp(-x)+1/(1/exp(1)-exp(1))*exp(x)+x