On Numerical Methods for Second Order PDE

This paper is composed of two sections. The job of the people such as Z. Cai. and R. Lazarov was introduced in the first section, their idea is to use first order system least squares for solving second order partial differential equations. The simplest case of first order elliptic system is Cauchy-Riemann equation, so the difference schemes of Cauchy-Riemann equation was studied in the second section.