Conservation Laws of Variable Coefficient Diffusion-Convection Equations

Abstract

We study local conservation laws of variable coefficient diffusion-convection equations of the form $f(x)u_t=(g(x)A(u)u_x)_x+h(x)B(u)u_x$. The main tool of our investigation is the notion of equivalence of conservation laws with respect to the equivalence groups. That is why, for the class under consideration we first construct the usual equivalence group $G^{\sim}$ and the extended one $\hat G^{\sim}$ including transformations which are nonlocal with respect to arbitrary elements. The extended equivalence group $\hat G^{\sim}$ has interesting structure since it contains a non-trivial subgroup of gauge equivalence transformations. Then, using the most direct method, we carry out two classifications of local conservation laws up to equivalence relations generated by $G^{\sim}$ and $\hat G^{\sim}$, respectively. Equivalence with respect to $\hat G^{\sim}$ plays the major role for simple and clear formulation of the final results.