Construction of exact solutions in implicit form for PDEs: New functional separable solutions of non-linear reaction–diffusion equations with variable coefficients

The paper deals with different classes of non-linear reaction–diffusion equations with variable coefficients c(x)ut=[a(x)f(u)ux]x+b(x)g(u),that admit exact solutions. The direct method for constructing functional separable solutions to these and more complex non-linear equations of mathematical physics is described. The method is based on the representation of solutions in implicit form ∫h(u)du=ξ(x)ω(t)+η(x),where the functions h(u), ξ(x), η(x), and ω(t) are determined further by analyzing the resulting functional-differential equations. Examples of specific reaction–diffusion type equations and their exact solutions are given. The main attention is paid to non-linear equations of a fairly general form, which contain several arbitrary functions dependent on the unknown u and /or the spatial variable x (it is important to note that exact solutions of non-linear PDEs, that contain arbitrary functions and therefore have significant generality, are of great practical interest for testing various numerical and approximate analytical methods for solving corresponding initial–boundary value problems). Many new generalized traveling-wave solutions and functional separable solutions are described. •Exact solutions are sought in the implicit form.•Non-linear reaction–diffusion equations are considered.•Arbitrary functions are included in equations.•New functional separable solutions are presented.•New generalized traveling-wave solutions are obtained.