## A free boundary problem for the Fisher-KPP equation with a given moving boundary.(English)Zbl 1397.35348

Summary: We study free boundary problem of Fisher-KPP equation $$u_t = u_{xx}+u(1-u)$$, $$t>0$$, $$ct<x<h(t)$$. The number $$c>0$$ is a given constant, $$h(t)$$ is a free boundary which is determined by the Stefan-like condition. This model may be used to describe the spreading of a non-native species over a one dimensional habitat. The free boundary $$x = h(t)$$ represents the spreading front. In this model, we impose zero Dirichlet condition at left moving boundary $$x = ct$$. This means that the left boundary of the habitat is a very hostile environment and that the habitat is eroded away by the left moving boundary at constant speed $$c$$.
In this paper we will give a trichotomy result, that is, for any initial data, exactly one of the three behaviors, vanishing, spreading and transition, happens. This result is related to the results appear in the free boundary problem for the Fisher-KPP equation with a shifting-environment, which was considered by Y. Du et al. [“Spreading in a shifting environment modeled by the diffusive logistic equation with a free boundary”, J. Dyn. Differ. Equations (to appear)]. However the vanishing in our problem is different from that in [loc. cit.] because in our vanishing case, the solution is not global-in-time.

### MSC:

 35R35 Free boundary problems for PDEs 35K20 Initial-boundary value problems for second-order parabolic equations 35K55 Nonlinear parabolic equations 35K57 Reaction-diffusion equations 35K58 Semilinear parabolic equations
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