关键词: 偏微分方程组, 秩, 特征值, 椭圆型方程组, Dirichlet 问题

Abstract:  In this paper the systems of linear partial differential equations of second order with three unknown functions are deduced．The sufficient and necessary conditions of decomposition of the systems are achieved．This condition is connected only with coefficients and characteristic values．

Key words: systems of partial differential equations, rank, eigenvalue, elliptic system of equations, Dirichlet’s problem