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We establish the logarithmic Bramson correction to the position of solutions to the Fisher--KPP equation with nonlocal diffusion. Solutions with step-like initial data typically resemble a front at position $c_{*} t - \frac{3}{2…

Analysis of PDEs · Mathematics 2020-05-13 Cole Graham

We consider the solution to the scalar Fisher-KPP equation with front-like initial data, focusing on the location of its level sets at large times, particularly their deviation from points moving at the known spreading speed. We consider an…

Analysis of PDEs · Mathematics 2024-10-11 Matthieu Alfaro , Thomas Giletti , Dongyuan Xiao

We study the long time behavior of solutions of periodic Fisher-KPP type equations in $\mathbb{R}^n$ that arise from compactly supported initial data. We prove that propagation along a fixed direction $e\in\mathbb{S}^{n-1}$ is completely…

Analysis of PDEs · Mathematics 2019-10-21 Beniada Shabani

For a simple one dimensional lattice version of a travelling wave equation, we obtain an exact relation between the initial condition and the position of the front at any later time. This exact relation takes the form of an inverse problem:…

Statistical Mechanics · Physics 2015-09-30 Éric Brunet , Bernard Derrida

We study the one-dimensional Fisher-KPP equation, with an initial condition $u_0(x)$ that coincides with the step function except on a compact set. A well-known result of M. Bramson states that, as $t\to+\infty$, the solution converges to a…

Analysis of PDEs · Mathematics 2018-04-19 James Nolen , Jean-Michel Roquejoffre , Lenya Ryzhik

In this paper, we investigate the location of the spreading front and convergence to traveling wave profile of solutions to the Fisher-KPP equation in the following two cases: (i) in unbounded domains with an expanding boundary; (ii) on the…

Analysis of PDEs · Mathematics 2025-09-16 King-Yeung Lam , Chang-Hong Wu

We consider a class of reaction-diffusion equations of Fisher-KPP type in which the nonlinearity (reaction term) $f$ is merely $C^1$ at $u=0$ due to a logarithmic competition term. We first derive the asymptotic behavior of (minimal speed)…

Analysis of PDEs · Mathematics 2020-09-03 Emeric Bouin , Christopher Henderson

We study the large time asymptotics of a solution of the Fisher-KPP reaction-diffusion equation, with an initial condition that is a compact perturbation of a step function. A well-known result of Bramson states that, in the reference frame…

Analysis of PDEs · Mathematics 2016-06-20 James Nolen , Jean-Michel Roquejoffre , Lenya Ryzhik

We consider solutions of the KPP-type equations with a periodically varying reaction rate, and compactly supported initial data. It has been shown by M. Bramson in the case of the constant reaction rate that the lag between the position of…

Analysis of PDEs · Mathematics 2012-11-28 Francois Hamel , James Nolen , Jean-Michel Roquejoffre , Lenya Ryzhik

We consider the large time behaviour of solutions to the porous medium equation with a Fisher-KPP type reaction term and nonnegative, compactly supported initial function in $L^\infty(\mathbb{R}^N)\setminus\{0\}$: \begin{equation}…

Analysis of PDEs · Mathematics 2018-06-07 Yihong Du , Fernando Quiros , Maolin Zhou

We study a Fisher-KPP equation with spatially periodic diffusion and reaction terms. We identify a class of periodic media for which the equation admits an explicit, closed-form solution. Through a nonlinear change of variables, the problem…

Analysis of PDEs · Mathematics 2025-12-09 Lionel Roques

In this work we investigate the issue of logarithmic drifts in the position of the level sets of solutions of monostable reaction-diusion equations, with respect to the traveling front with minimal speed. On the one hand, it is a celebrated…

Analysis of PDEs · Mathematics 2022-08-29 Thomas Giletti

We provide the first PDE proof of the celebrated Bramson's $o(1)$ results in 1983 concerning the large time asymptotics for the KPP equation under front-like initial data of types $x^{k+1}e^{-\lambda_*x}$ and $x^{\boldsymbol{\nu}}…

Analysis of PDEs · Mathematics 2025-06-12 Mingmin Zhang

We study the asymptotic behaviour, as time goes to infinity, of the Fisher-KPP equation $\partial_t u=\Delta u +u-u^2$ in spatial dimension $2$, when the initial condition looks like a Heaviside function. Thus the solution is,…

Analysis of PDEs · Mathematics 2017-02-28 Jean-Michel Roquejoffre , Violaine Roussier-Michon

We study a variant of the Fisher-KPP equation with nonlocal dispersal. Using the theory of large deviations, we show the emergence of a "Bramson-like" logarithmic delay for the linearised equation with step-like initial data. We conclude…

Analysis of PDEs · Mathematics 2024-01-19 Nathanaël Boutillon

The free boundary problem\[ \begin{cases} \partial_tu=\frac{1}{2}\Delta u+u,\quad &t>0, \, x>L_t,\\ u(t,x)=0,\quad &t>0,\, x\le L_t,\\ \int_{L_t}^{\infty}u(t,y)dy=1,\quad &t> 0,\\ u(t,x)dx \to u_0(dx)&\text{weakly as }t\to 0, \end{cases}\]…

Analysis of PDEs · Mathematics 2025-12-01 Julien Berestycki , Sarah Penington , Oliver Tough

The present work concerns a version of the Fisher-KPP equation where the nonlinear term is replaced by a saturation mechanism, yielding a free boundary problem with mixed conditions. Following an idea proposed in [BrunetDerrida.2015], we…

Statistical Mechanics · Physics 2018-01-17 Julien Berestycki , Éric Brunet , Bernard Derrida

Take the linearised FKPP equation \[\partial_t h =\partial^2_x h +h\] with boundary condition $h(m(t),t)=0$. Depending on the behaviour of the initial condition $h_0(x)=h(x,0)$ we obtain the asymptotics - up to a $o(1)$ term $r(t)$ - of the…

Probability · Mathematics 2017-02-08 Julien Berestycki , Éric Brunet , Simon C. Harris , Matthew I. Roberts

This paper presents a novel way of computing front positions in Fisher-KPP equations. Our method is based on an exact relation between the Laplace transform of the initial condition and some integral functional of the front position. Using…

Statistical Mechanics · Physics 2018-06-13 Julien Berestycki , Éric Brunet , Bernard Derrida

This paper investigates the existence of almost periodic traveling fronts for Fisher-KPP lattice equations in one-dimensional almost periodic media. By the Lyapunov exponent of the linearized operator near the unstable steady state, we give…

Analysis of PDEs · Mathematics 2021-04-29 Xing Liang , Hongze Wang , Qi Zhou , Tao Zhou
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