Nonclassical symmetry reductions and conservation laws for reaction-diffusion equations with application to population dynamics

Abstract

This dissertation analyses the reaction-di usion equations, in particular the modi ed Huxley model, arising in population dynamics. The focus is on determining the classical Lie point symmetries, and the construction of the conservation laws and group-invariant solutions for reaction-di usion equations. The invariance criterion for determination of classical Lie point symmetries results in a system of linear determining equations which can be solved analytically. Furthermore, the Lie point symmetries associated with the conservation laws are determined. Reductions by associated Lie point symmetries are carried out. Nonclassical symmetry techniques are also employed. Here the invariance criterion for symmetry determination results in a system of nonlinear determining equations which may be solved albeit di cult. Nonclassical symmetries results in exact solutions which may not be constructed by classical Lie point symmetries. The highlight in construction of exact solution using nonclassical symmetries is the introduction of the modi ed Hopf-Cole transformation. In this dissertation, the di usion term and the coe cient of the source term are given as quadratic functions of space variable in one case, and the coe cient as the generalised power law in the other. These equations admit a number of classical Lie point symmetries. The genuine nonclassical symmetries are admitted when the source term of the reaction-di usion equation is a cubic.