S. Bertone, A. Cellina, E. M. Marchini
In this paper we consider Hopf's Lemma and the Strong Maximum Principle for supersolutions to a class of non elliptic equations. In particular we prove a sufficient condition for the validity of Hopf's Lemma and of the Strong Maximum Principle and we give a condition which is at once necessary for the validity of Hopf's Lemma and sufficient for the validity of the Strong Maximum Principle.
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In this paper, we first establish Hopf's lemmas for parabolic fractional equations and parabolic fractional $p$-equations. Then we derive an asymptotic Hopf's lemma for antisymmetric solutions to parabolic fractional equations. We believe that these Hopf's lemmas will become powerful tools in obtaining qualitative properties of solutions for nonlocal parabolic equations.
This, and its sequel, concern some variations of a classical theorem of A.D. Alexandrov and teh Hopf Lemma.
We give a Hopf boundary point lemma for weak solutions of linear divergence form uniformly elliptic equations, with H$\ddot{\text{o}}$lder continuous top-order coefficients and lower-order coefficients in a Morrey space.
We discuss the problem how "bad" may be lower-order coefficients in elliptic and parabolic second order equations to ensure the Hopf--Oleinik Lemma for solutions to hold true. We also touch the gradient estimates for solutions at the boundary.
This paper concerns Hopf's boundary point lemma, in certain $C^{1,Dini}$-type domains, for a class of singular/degenerate PDE-s, including $p$-Laplacian. Using geometric properties of levels sets for harmonic functions in convex rings, we construct sub-solutions to our equations that play the role of a barrier from below. By comparison principle we then conclude Hopf's lemma.
In this short article, we state a Hopf type lemma for fractional equations and the outline of its proof. We believe that it will become a powerful tool in applying the method of moving planes on fractional equations to obtain qualitative properties of solutions.
Antisymmetric maximum principles and Hopf's lemmas for the Logarithmic Laplacian, with applications to symmetry results
本文为对数拉普拉斯算子建立反对称最大值原理和Hopf型引理，并应用于证明半线性问题解的对称性及平行曲面问题的刚性结果。
We consider a class of quasi-linear anisotropic elliptic equations, possibly degenerate or singular, which are of interest in several applications such as computer vision and continuum mechanics. We prove a Hopf Lemma as well as local and global regularity estimates for positive solutions, generalizing previous results known in the context of p-Laplacian equations.
In this paper, we study qualitative properties of the fractional $p$-Laplacian. Specifically, we establish a Hopf type lemma for positive weak super-solutions of the fractional $p-$Laplacian equation with Dirichlet condition. Moreover, an optimal condition is obtained to ensure $(-\triangle)_p^s u\in C^1(\mathbb{R}^n)$ for smooth functions $u$.
We show a Hopf boundary point lemma for $u=u_{1}-u_{2},$ given $u_{1},u_{2} \in C^{1,α}$ each weak solutions to a quasilinear equation $\sum_{i=1}^{n} D_{i}(A^{i}(x,u,Du))+B(x,u,Du)=0$ under mild boundedness assumptions on $A^{1},\ldots,A^{n},B.$
We prove a Hopf's lemma in the point-wise sense. The essential technique is to prove $(-Δ)^s_p u(x)$ is uniformly bounded in the unit ball $B_1\subset\mathbb{R}^n$, where $u(x)=(1-|x|^2)^s_{+}$. Also we study the global Hölder continuity of bounded positive solutions for $(-Δ)^s_p u(x)=f(x,u).$
We begin the paper with a Hopf's lemma for a fractional p-Laplacian problem on a half-space. Specifically speaking, we show that the derivative of the solution along the outward normal vector is strictly positive on the boundary of the half-space. Next we show that positive solutions to a fractional p-Laplacian equation possess certain Holder continuity up to the boundary.
We construct a new counterexample confirming the sharpness of the Dini-type condition for the boundary of $Ω$. In particular, we show that for convex domains the Dini-type assumption is the necessary and sufficient condition which guarantees the Hopf-Oleinik type estimates.
Optimal boundary regularity and a Hopf-type lemma for Dirichlet problems involving the logarithmic Laplacian
本文研究涉及对数拉普拉斯算子的狄利克雷问题，利用Kelvin变换构造障碍函数证明最优边界正则性，并由此得到非负弱解的Hopf型引理及非线性问题解的唯一性。
The classical Hopf's lemma can be reformulated as uniqueness of continuation result. We aim in the present work to quantify this property. We show precisely that if a solution $u$ of a divergence form elliptic equation attains its maximum at a boundary point $x_0$ then both $L^1$-norms of $u-u(x_0)$ on the domain and on the boundary are bounded, up to a multiplicative constant, by the exterior normal derivative at $x_0$.
Our propose here is to provide a Hopf Lemma and a strong minimum principle for week supersolutions of \[ (-Δ_p)^s u= c(x)|u|^{p-2}u \quad \text{ in } Ω\] where $Ω$ is an open set of $\mathbb{R}^N,$ $s\in(0,1),$ $p\in(1,+\infty),$ $c\in C(\overlineΩ)$ and $(-Δ_p)^s$ is the fractional $p$-Laplacian.
Hopf's lemmas and boundary point results for the fractional $p$-Laplacian
本文针对分数阶 $p$-拉普拉斯算子（$p \geq 2$）建立了Hopf边界引理的新证明，并推广到变号势情形，无需全局符号条件，且应用于边界点引理和非局部超定问题。
We provide a Hopf boundary lemma for the regional fractional Laplacian $(-Δ)^s_Ω$, with $Ω\subset\mathbb{R}^N$ a bounded open set. More precisely, given $u$ a pointwise or weak super-solution of the equation $(-Δ)^s_Ω u = c(x)u$ in $Ω$, we show that the ratio $u(x)/(\mathrm{dist}(x,\partialΩ))^{2s-1}$ is strictly positive as $x$ approaches the boundary $\partialΩ$ of $Ω$. We also prove a strong maximum principle for distributional super-solutions.
This paper deals with a theoretical mathematical analysis of a one-dimensional-moving-boundary problem for the time-fractional diffusion equation, where the time-fractional derivative of order $\al$ $\in (0,1)$ is taken in the Caputo's sense. A generalization of the Hopf's lemma is proved, and then this result is used to prove a monotonicity property for the free-boundary when a fractional free-boundary Stefan problem is considered.
Hopf-Oleinik lemma for elliptic equations in double divergence form
本文首次为双重散度形式的均匀椭圆方程建立了Zaremba-Hopf-Oleinik型边界点引理，并据此在$C^{1,α}$区域中得到了非散度形式二阶椭圆方程Green函数的精确双边估计。
Hopf's lemmas and boundary behaviour of solutions to the fractional Laplacian in Orlicz-Sobolev spaces
本文在Orlicz-Sobolev空间框架下，将Hopf边界引理推广到分数阶$a-$拉普拉斯算子，研究满足内部球条件的区域边界附近解的行为，并同时处理常号与变号位势问题。
A fractional Hopf Lemma for sign-changing solutions
本文研究了分数阶椭圆问题解的边界行为，在不对解的符号作全局假设的条件下建立了 Hopf 引理，并证明非平凡径向解在边界处不能有无穷多个零点累积，同时给出实例证明结果精确性。
Boundary regularity and Hopf lemma for nondegenerate stable operators
本文针对满足外部C^{1,dini}性质的有界开集，证明了非退化稳定积分微分算子方程解的尖锐边界Hölder正则性与Hopf型边界引理，并展示了估计在s→1-时的稳健性，从而恢复二阶方程经典结果。
Boundary Lipschitz Regularity and the Hopf Lemma on Reifenberg Domains for Fully Nonlinear Elliptic Equations
该研究针对完全非线性椭圆方程，提出统一方法证明Reifenberg区域上的边界Lipschitz正则性与Hopf引理，明确内外Reifenberg $C^{1,\mathrm{Dini}}$条件对应的成立情形，拓展了常规条件下的已有结论。
Let $Ω\subset \mathbb{R}^n $ be any open set and $u$ be a weak supersolution of $\mathcal{L}u=c(x)g(|u|)\frac{u}{|u|}$ where \[\mathcal{L}u(x)=\text{p.v.} \int_{\mathbb{R}^n} g\left(\frac{|u(x)-u(y)|}{|x-y|^s}\right) \frac{u(x)-u(y)}{|u(x)-u(y)|} K(x,y)\frac{dy}{|x-y|^s}\] and $g=G^{\prime}$ for some Young function $G.$ This note imparts a Hopf's type lemma and strong minimum principle for $u$ when $c(x)$ is continuous in $\barΩ$ that extend the results of Del Pezzo and Quaas (JDE-2017) in fractional Orlicz-Sobolev setting.
On Hopf's Lemma for sign-changing supersolutions to fractional Laplacian equations
本文研究了分数拉普拉斯方程中变号超解的霍普夫引理有效性，通过扩展方法将其与边界点的霍普夫引理联系起来，并改进了最近关于二元性结果的分析。
A quantitative Hopf-Oleinik lemma for degenerate fully nonlinear operators and applications to free boundary problems
本文提出了一种针对退化全非线性算子的定量Hopf-Oleinik引理，并应用于自由边界问题和火焰传播模型的正则性研究。
Hopf's lemma for parabolic equations involving a generalized tempered fractional $p$-Laplacian
本文针对含广义缓变分数阶$p$-Laplacian的非线性抛物系统，建立了相应的Hopf引理，为研究非局部抛物方程解的定性性质提供了有力工具。
Boundary Lipschitz Regularity and the Hopf Lemma for Fully Nonlinear Elliptic Equations
针对完全非线性椭圆方程粘性解的边界正则性问题，提出将曲边界视为超平面扰动的统一简洁方法，证明内外C^{1,\text{Dini}}条件分别对应边界Lipschitz连续性与Hopf引理成立，并验证该条件的最优性。
Global gradient regularity and a Hopf lemma for quasilinear operators of mixed local-nonlocal type
本文针对p-Laplacian与分数阶(s, q)-Laplacian之和构成的混合局部-非局部拟线性算子，在边界仅为C^{1, α}且p > s q的条件下，证明了弱解到边界的C^{1, θ}正则性，并建立了正上解的Hopf型引理。
The Hopf Lemma for second order elliptic operators is proved to hold in domains with $C^{1,α}$, and even less regular, boundaries. It need not hold for $C^1$ boundaries. Corresponding results are proved for second order parabolic operators.
A classical theorem of A.D. Alexandrov says that a connected compact smooth hypersurface in Euclidean space with constant mean curvature must be a sphere. We give exposition to some results on symmetry properties of hypersurfaces with ordered mean curvature and associated variations of the Hopf Lemma. Some open problems will be discussed.
In [1], Theorem 3, the authors proved, in one dimension, a generalization of the Hopf Lemma, and the question arose if it could be extended to higher dimensions. In this paper we present two conjectures as possible extensions, and give a very partial answer. We write this paper to call attention to the problem.
In the present paper we prove estimates on {subsolutions of the equation $-Av+c(x)v=0$}, $x\in D$, where $D\subset \bbR^d$ is a domain (i.e. an open and connected set) and $A$ is an integro-differential operator of the Waldenfels type, whose differential part satisfies the uniform ellipticity condition on compact sets. In general, the coefficients of the operator need not be continuous but only bounded and Borel measurable. Some of our results may be considered "quantitative" versions of the Hopf lemma, as they provide the lower bound on the outward normal directional derivative at the maximum…
The paper establishes a version of the Hopf boundary point lemma for sections of a vector bundle over a manifold with boundary. This result may be viewed as a counterpart to the tensor maximum principle obtained by R. Hamilton in 1986. Potential applications include the study of various geometric flows and the construction of invariant sets for geometric boundary value problems.
We consider a large family of integro-differential equations and establish a non-local counterpart of Hopf's lemma, directly expressed in terms of the symbol of the operator. As closely related problems, we also obtain a variety of maximum principles for viscosity solutions. In our approach we combine direct analysis with functional integration, allowing a robust control around the boundary of the domain, and make use of the related ascending ladder height-processes. We then apply these results to a study of principal eigenvalue problems, the radial symmetry of the positive solutions, and the …
The Hopf lemma for the Schrödinger operator
本文证明了在势能仅属于 $L_{\mathrm{loc}}^1(Ω)$ 的非负条件下，涉及Schrödinger算子的Dirichlet问题解的Hopf边界点引理，并利用Hopf引理失效的集合刻画了使相应边值问题有解的非负有限Borel测度。
A classical result of A.D. Alexandrov states that a connected compact smooth $n-$dimensional manifold without boundary, embedded in $\Bbb R^{n+1}$, and such that its mean curvature is constant, is a sphere. Here we study the problem of symmetry of $M$ in a hyperplane $X_{n+1}=$constant in case $M$ satisfies: for any two points $(X', X_{n+1})$, $(X', \hat X_{n+1})$ on $M$, with $X_{n+1}>\hat X_{n+1}$, the mean curvature at the first is not greater than that at the second. Symmetry need not always hold, but in this paper, we establish it under some additional conditions. Some variations of the H…
In this paper we provide another application of the Inhomogeneous Hopf-Ole\uınik Lemma (IHOL) proved in \cite{BM-IHOL-PartI} or \cite{Boyan-2}. As a matter of fact, we also provide a new and simpler proof of a slightly weaker version IHOL for the uniformly elliptic fully nonlinear case which is sufficient for most purposes. The paper has essentially two parts. In the first part, we use IHOL for unbounded RHS to develop a Caffarelli's "Lipschitz implies $C^{1,α}$" approach to prove Ladyzhenskaya-Uraltseva boundary gradient type estimates for functions in $S^{*}(γ, f)$ that vanishes on the bound…
Failure of the Hopf-Oleinik lemma for a linear elliptic problem with singular convection of non-negative divergence
本文研究了具有非负散度奇异对流的线性椭圆 Dirichlet 问题，将解的存在性理论推广至 $|E| \in L^2$ 并证明了比较原理，同时揭示此类奇异漂移项会导致 Hopf-Oleinik 引理失效。
We obtain a global extension of the classical weak Harnack inequality which extends and quantifies the Hopf-Oleinik boundary-point lemma, for uniformly elliptic equations in divergence form. Among the consequences is a boundary gradient estimate, due to Krylov and well-studied for non-divergence form equations, but completely novel in the divergence framework. Another consequence is a new more general version of the Hopf-Oleinik lemma.
We present several results, including some remarks on the Hopf Lemma.
The paper concerns singular solutions of nonlinear elliptic equations, which include removable singularities for viscosity solutions, a strengthening of the Hopf Lemma including parabolic equations, Strong maximum principle and Hopf Lemma for viscosity solutions including also parabolic equations.
We prove a sharp version of the Hopf boundary point lemma for Black-Scholes type equations. We also investigate the existence and the regularity of the spatial derivative of the solutions at the spatial boundary.
We provide some versions of the Zaremba-Hopf-Oleinik boundary point lemma for general elliptic and parabolic equations in divergence form under the sharp requirements on the coefficients of equations and on the boundaries of domains.
This survey provides a description of the history and the state of the art of one of the most important fields in the qualitative theory of elliptic partial differential equations including the strong maximum principle, the boundary point principle (the normal derivative lemma) and related topics.
We consider elliptic equations with non-Lipschitz nonlinearity $$ -Δu = λ|u|^{β-1}u-|u|^{α-1}u$$ in a smooth bounded domain $Ω\subset \mathbb{R}^n$, $n\geq 3$, with Dirichlet boundary conditions; here $0<α<β<1$. We prove the existence of a weak nonnegative solution which does not satisfy the Hopf boundary maximum principle, provided that $λ$ is large enough and $n>2(1+α) (1+β)/(1-α)(1-β)$.
The role of antisymmetric functions in nonlocal equations
本文建立带零阶项分数阶 Laplace 算子反对称超解的 Hopf 型引理，并结合移动平面法证明半线性分数阶平行曲面问题的径向对称性与区域为球，同时讨论相关最大值原理、Harnack 不等式及局部假设下的反例。
In this paper, we obtain the strong comparison principle and Hopf Lemma for locally Lipschitz viscosity solutions to a class of nonlinear degenerate elliptic operators of the form $\nabla^2 ψ+ L(x,\nabla ψ)$, including the conformal hessian operator.
Boundary behavior of solutions to fractional $p$-Laplacian equation
该研究针对分数阶$p$-拉普拉斯方程，证明了其解的广义Hopf引理与全局边界Harnack不等式，并得出满足Wiener准则的有界开集中第一$(s,p)$-特征值具有孤立性的结论。
We establish via variational methods the existence of a standing wave together with an estimate on the convergence to its asymptotic states for a bistable system of partial differential equations on a periodic domain. The main tool is a replacement lemma which has as a corollary a maximum principle for local minimizers.
We consider a class of fully nonlinear nonlocal degenerate elliptic operators which are modeled on the fractional Laplacian and converge to the truncated Laplacians. We investigate the validity of (strong) maximum and minimum principles, and their relation with suitably defined principal eigenvalues. We also show a Hopf type Lemma, the existence of solutions for the corresponding Dirichlet problem, and representation formulas in some particular cases.
We give a simple proof of the strong maximum principle for viscosity subsolutions of fully nonlinear elliptic PDEs on the form $$ F(x,u,Du,D^2u) = 0 $$ under suitable structure conditions on the equation allowing for non-Lipschitz growth in the gradient terms. In case of smooth boundaries, we also prove the Hopf lemma, the boundary Harnack inequality and that positive viscosity solutions vanishing on a portion of the boundary are comparable with the distance function near the boundary. Our results apply to weak solutions of an eigenvalue problem for the variable exponent $p$-Laplacian.
In this survey we consider the classical overdetermined problem which was studied by Serrin in 1971. The original proof relies on Alexandrov's moving plane method, maximum principles, and a refinement of Hopf's boundary point Lemma. Since then other approaches to the same problem have been devised. Among them we consider the one due to Weinberger which strikes for the elementary arguments used and became very popular. Then we discuss also a duality approach involving harmonic functions, a shape derivative approach and a purely integral approach, all of them not relying on maximum principle. Fo…
We present some comparison results for solutions to certain non local elliptic and parabolic problems that involve the fractional Laplacian operator and mixed boundary conditions, given by a zero Dirichlet datum on part of the complementary of the domain and zero Neumann data on the rest. These results represent a non local generalization of a Hopf's lemma for elliptic and parabolic problems with mixed conditions. In particular we prove the non local version of the results obtained by J. Dávila and J. Dávila-L. Dupaigne for the classical case respectively.
In this short note we extend Chow and Lu's advanced maximum principles for parabolic systems on closed manifolds to the case of compact manifolds with boundary, which also generalizes a Hopf type theorem of Pulemotov.
In this work we prove a strong maximum principle for fractional elliptic problems with mixed Dirichlet-Neumann boundary data which extends the one proved by J. Dávila to the fractional setting. In particular, we present a comparison result for two solutions of the fractional Laplace equation involving the spectral fractional Laplacian endowed with homogeneous mixed boundary condition. This result represents a non-local counterpart to a Hopf's Lemma for fractional elliptic problems with mixed boundary data.
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