The Extrapolation Of The Eigenvalue Problem Using Bilinear Element

In this paper, we expand eigenvalue of Poisson equation using bilinear element,By the formulation of the error expanition,we can conclude that it is a upper bound.And by two numerical example,we computer the approximate eigenvalue of Poisson equation in square and L-shape domains,then we analyses the approximate eigenvalue.we also extraplate the error expansion and enhance the accuracy of the eigenvalue form the second order to the forth order.