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Symmetries and form-preserving transformations of generalised inhomogeneous nonlinear diffusion equations. (English) Zbl 1024.35042
Summary: We consider the variable coefficient inhomogeneous nonlinear diffusion equations of the form f(x)u t =[g(x)u n u x ] x . We present a complete classification of Lie symmetries and form-preserving point transformations in the case where f(x)=1 which is equivalent to the original equation. We also introduce certain nonlocal transformations. When f(x)=x p and g(x)=x q we have the most known form of this class of equations. If certain conditions are satisfied, then this latter equation can be transformed into a constant coefficient equation. It is also proved that the only equations from this class of partial differential equations that admit Lie-Bäcklund symmetries is the well-known nonlinear equation u t =[u -2 u x ] x and an equivalent equation. Finally, two examples of new exact solutions are given.
MSC:
35K55Nonlinear parabolic equations
58J72Correspondences and other transformation methods (PDE on manifolds)
58J70Invariance and symmetry properties
35C05Solutions of PDE in closed form