A Function Of Frequency

A Frequency function was first introduced Almgren. Frequency function has become a powerful tool in proving unique continuation of equations.First, the article describes some of the basic properties of frequency function, the rescults based on Linfang Hua Han Qing’s work on zero measurable set of elliptic equations. Chapter one mainly introduce the classic double theorem, including Harmonic Type Systems and Elliptic Equations in Divergence double Theorem.Secondly,chapter two introduces the unique continuation theorem results of nonlinear equations, those rescults based on Granlund and Marola’s work, and the latest work of Armstrong and Silverstre in the fully nonlinear equations.The last chapter gives a unique continuation with gradient elliptic equations, from the classic Harmonic function to results with gradient elliptic equations.