计算二维薄板应力与应变，采用平面四节点板单元，精度较高。(The stress and strain of two dimensional thin plate are calculated. The plane four node plate element is used to calculate the stress and strain of the plate.)

在matlab中实现四节点板单元刚度矩阵求解，振动模态分析(Realize the solution of the stiffness matrix of the four-node plate element and the vibration modal analysis in matlab.)