1引言有限元导数恢复技术是近年来发展起来的计算有限元导数并获得导数逼近超收敛性的一种新的后处理技术.对于一维和二维区域上的二阶椭圆边值问题,文[1,2]提出了Z-Z小片插值技术,得到了有限元导数逼近在小片恢复区域上的一阶超收敛结果和剖分节点处二阶强超收敛性;文[3,4]则建立了更为实用的小片插值恢复技术并得到与文[1,2]相平行的超收敛结果;文[5] 对两点边值问题构造了一种积分形式的导数恢复公式,利用这个公式可获得剖分节点处有限元导数逼近的O(h^2k))阶超收敛估计.本文将对一维四阶椭圆
A two-order derivative recovery formula is presented for the finite element approximations to the 4th-order elliptic boundary value problems in one space dimension, It is proved that this formula possesses the ultraconvergence that is two order higher than the optimal convergence order on the whole domain in W^2∞ norm. Numerical experiments are given to confirm the efficiency of our formula.