DefinitionMathematically they are used to solve inhomogeneous differntial equations that has some particular boundary conditions. They're are the impulse response of a linear system and they used for convert solution of the differential equation to an integral representation. Green's functions are used as a mathematical representation of the operation of a linear differential operator, or more generally by a linear operator. They are used in physics, engineering, and other fields to solve certain properties functions of the Green's function can be used to represent the behavior of certain operating systems or material properties. Eg: There is a differential operator L, an inhomogeneous term f(x), then solution u(x) can be written as u(x)=∫G(x,x′)f(x′)dx′, here G(x,x′) is the Greens function for L