The Squeeze Theorem and the Upper-lower Solution Methods for Parabolic Partial Defferential Equation

The paper applies the criteria for limit squeezing principle to parabolic partial differential equations.Through the introduction of upper and lower solution,a string of non-monotonous sequence of solution and a string of non-monotonous solution by the next sequence are constructed,which proves the unique existence of the solution of semi-linear parabolic partial differential equation boundary value problems.