## Differential and Integral Equations

- Differential Integral Equations
- Volume 22, Number 5/6 (2009), 587-600.

### Coincidence sets associated with second-order ordinary differential equations of logistic type

#### Abstract

This paper concerns the formation of a coincidence set for the positive solution of the boundary-value problem $-{\varepsilon} (\phi_p(u_x))_x= \phi_q(u)f(c(x)-u)$ in $I=(-1,1)$ with $u(\pm 1)=0$, where ${\varepsilon}$ is a positive parameter, $\phi_p(s)=|s|^{p-2}s,\ 1 < q \le p < \infty$, $f(s) \sim \phi_{\theta+1}(s)\ (s \to 0)$, $0 < \theta < \infty$ and $c(x)$ is a positive smooth function satisfying $(\phi_p(c_x))_x=0$ in $I$. The positive solution $u_{\varepsilon}(x)$ converges to $c(x)$ uniformly on any compact subset of $I$ as ${\varepsilon} \to 0$. It is known that if $c(x)$ is constant and $\theta < p-1$, then the solution coincides with $c(x)$ somewhere in $I$ for sufficiently small ${\varepsilon}$ and the coincidence set $I_{\varepsilon}=\{x\in I : u_{\varepsilon}(x)=c(x)\}$ converges to $I$ as $|I \setminus I_{\varepsilon}| \sim {\varepsilon}^{1/p}\ ({\varepsilon} \to 0)$. It is proved in this paper that even if $c(x)$ is variable and $\theta < 1$, then $I_{\varepsilon}$ has a positive measure and converges to $I$ with order $O({\varepsilon}^{\kappa})$ as ${\varepsilon} \to 0$, where $\kappa=\min\{1/p,1/2\}$. Moreover, it is also shown that, if $\theta \ge 1$, then $I_{\varepsilon}$ is empty for every ${\varepsilon}$. The proofs rely on comparison principles and an energy method for obtaining local comparison functions.

#### Article information

**Source**

Differential Integral Equations Volume 22, Number 5/6 (2009), 587-600.

**Dates**

First available in Project Euclid: 20 December 2012

**Permanent link to this document**

https://projecteuclid.org/euclid.die/1356019608

**Mathematical Reviews number (MathSciNet)**

MR2501686

**Zentralblatt MATH identifier**

1240.34118

**Subjects**

Primary: 34E15: Singular perturbations, general theory

Secondary: 34B15: Nonlinear boundary value problems 34C11: Growth, boundedness

#### Citation

Takeuchi, Shingo. Coincidence sets associated with second-order ordinary differential equations of logistic type. Differential Integral Equations 22 (2009), no. 5/6, 587--600. https://projecteuclid.org/euclid.die/1356019608.