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We show that a general nonlinearity $a(x,u)$ is uniquely determined, possibly up to a gauge, in a neighborhood of a fixed solution from boundary measurements of the corresponding semilinear equation. The main theorems are low regularity…

Analysis of PDEs · Mathematics 2026-05-08 David Johansson , Janne Nurminen , Mikko Salo

We study inverse source problems associated to semilinear elliptic equations of the form \[ \Delta u(x)+a(x,u)=F(x), \] on a bounded domain $\Omega\subset \mathbb{R}^n$, $n\geq 2$. We show that it is possible to use nonlinearity to break…

Analysis of PDEs · Mathematics 2023-02-15 Tony Liimatainen , Yi-Hsuan Lin

We study various partial data inverse boundary value problems for the semilinear elliptic equation $\Delta u+ a(x,u)=0$ in a domain in $\mathbb R^n$ by using the higher order linearization technique introduced in [LLS 19, FO19]. We show…

Analysis of PDEs · Mathematics 2019-05-09 Matti Lassas , Tony Liimatainen , Yi-Hsuan Lin , Mikko Salo

We study the inverse problem of recovery a non-linearity $f(x,u)$, which is compactly supported in $x$, in the semilinear wave equation $u_{tt}-\Delta u+ f(x,u)=0$. We probe the medium with either complex or real-valued harmonic waves of…

Analysis of PDEs · Mathematics 2021-07-20 Antônio Sá Barreto , Plamen Stefanov

This paper is concerned with the forward and inverse problems for the fractional semilinear elliptic equation $(-\Delta)^s u +a(x,u)=0$ for $0<s<1$. For the forward problem, we proved the problem is well-posed and has a unique solution for…

Analysis of PDEs · Mathematics 2020-04-02 Ru-Yu Lai , Yi-Hsuan Lin

We initiate the study of inverse source problems for quasilinear elliptic equations of the form \[ \left\{ \begin{array}{ll} \nabla \cdot (\gamma(x,u,\nabla u) \nabla u) = F & \text{in } \Omega, \\ u = f & \text{on } \partial\Omega,…

Analysis of PDEs · Mathematics 2026-03-31 Tony Liimatainen , Shubham Jaiswal

We are concerned with the inverse boundary problem of determining anomalies associated with a semilinear elliptic equation of the form $-\Delta u+a(\mathbf x, u)=0$, where $a(\mathbf x, u)$ is a general nonlinear term that belongs to a…

Analysis of PDEs · Mathematics 2022-07-25 Huaian Diao , Xiaoxu Fei , Hongyu Liu , Li Wang

We study inverse problems for semilinear elliptic equations with fractional power type nonlinearities. Our arguments are based on the higher order linearization method, which helps us to solve inverse problems for certain nonlinear…

Analysis of PDEs · Mathematics 2020-12-10 Tony Liimatainen , Yi-Hsuan Lin , Mikko Salo , Teemu Tyni

We introduce a method for solving Calder\'on type inverse problems for semilinear equations with power type nonlinearities. The method is based on higher order linearizations, and it allows one to solve inverse problems for certain…

Analysis of PDEs · Mathematics 2019-04-01 Matti Lassas , Tony Liimatainen , Yi-Hsuan Lin , Mikko Salo

We study the inverse problem of unique recovery of a complex-valued scalar function $V:\mathcal M \times \mathbb C\to \mathbb C$, defined over a smooth compact Riemannian manifold $(\mathcal M,g)$ with smooth boundary, given the Dirichlet…

Analysis of PDEs · Mathematics 2023-05-10 Ali Feizmohammadi , Lauri Oksanen

In this work we analyze the existence of solutions to the nonlinear elliptic system: \begin{equation*} \left\{ \begin{array}{rcll} -\Delta u & = & v^q+\a g & \text{in }\Omega , \\ -\Delta v& = &|\nabla u|^{p}+\l f &\text{in }\Omega , \\…

Analysis of PDEs · Mathematics 2017-09-12 Boumediene Abdellaoui , Ahmed Attar , El-Haj Laamri

We consider the problem of reconstructing, from the interior data $u(x,1)$, a function $u$ satisfying a nonlinear elliptic equation $$ \Delta u = f(x,y,u(x,y)), x \in \RR, y > 0. $$

Analysis of PDEs · Mathematics 2009-11-11 Alain Pham Ngoc Dinh , Pham Hoang Quan , Dang Duc Trong

In this article we study the inverse problem of determining a semilinear term appearing in an elliptic equation from boundary measurements. Our main objective is to develop flexible and general theoretical results that can be used for…

Numerical Analysis · Mathematics 2024-11-18 Yavar Kian , Hongyu Liu , Li-Li Wang , Guang-Hui Zheng

This work derives explicit series reversions for the solution of Calder\'on's problem. The governing elliptic partial differential equation is $\nabla\cdot(A\nabla u)=0$ in a bounded Lipschitz domain and with a matrix-valued coefficient.…

Analysis of PDEs · Mathematics 2022-08-24 Henrik Garde , Nuutti Hyvönen

We study inverse problems for the nonlinear wave equation $\square_g u + w(x,u, \nabla_g u) = 0$ in a Lorentzian manifold $(M,g)$ with boundary, where $\nabla_g u$ denotes the gradient and $w(x,u, \xi)$ is smooth and quadratic in $\xi$.…

Analysis of PDEs · Mathematics 2021-11-02 Gunther Uhlmann , Yang Zhang

We consider the inverse problem of determining a general semilinear term appearing in nonlinear parabolic equations. For this purpose, we derive a new criterion that allows to prove global recovery of some general class of semilinear terms…

Analysis of PDEs · Mathematics 2020-11-13 Yavar Kian , Gunther Uhlmann

Given a conformally transversally anisotropic manifold $(M,g)$, we consider the semilinear elliptic equation $$(-\Delta_{g}+V)u+qu^2=0\quad \text{on $M$}.$$ We show that an a priori unknown smooth function $q$ can be uniquely determined…

Analysis of PDEs · Mathematics 2023-06-29 Ali Feizmohammadi , Tony Liimatainen , Yi-Hsuan Lin

This paper concerns an inverse boundary value problem of recovering a zeroth order time-dependent term of a semi-linear wave equation on a globally hyperbolic Lorentzian manifold. We show that an unknown potential $q$ in the non-linear wave…

Analysis of PDEs · Mathematics 2025-05-14 Matti Lassas , Tony Liimatainen , Leyter Potenciano-Machado , Teemu Tyni

This paper is concerned with the ubiquitous inverse problem of recovering an unknown function u from finitely many measurements possibly affected by noise. In recent years, inversion methods based on linear approximation spaces were…

Numerical Analysis · Mathematics 2022-10-06 Albert Cohen , Matthieu Dolbeault , Olga Mula , Agustin Somacal

We consider the inverse problem of determining a general nonlinear term appearing in a semilinear hyperbolic equation on a Riemannian manifold with boundary $(M,g)$ of dimension $n=2,3$. We prove results of unique recovery of the nonlinear…

Analysis of PDEs · Mathematics 2019-06-24 Yavar Kian
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