## Differential and Integral Equations

- Differential Integral Equations
- Volume 24, Number 3/4 (2011), 307-324.

### Positive solutions for $n\times n$ elliptic systems with combined nonlinear effects

Jaffar Ali, Ken Brown, and R. Shivaji

#### Abstract

We study the existence and multiplicity of positive solutions to $n\times n$ systems of the form \begin{align*} -\Delta u_1&=\lambda f_1(u_2)& \mbox{ in }\Omega\\ -\Delta u_2&=\lambda f_2(u_3)&\mbox{ in }\Omega\\ \vdots \quad &= \quad\vdots&\\ -\Delta u_{n-1}&=\lambda f_{n-1}(u_n)&\mbox{ in }\Omega\ \ -\Delta u_n&=\lambda f_n(u_1)&\mbox{ in }\Omega\\ u_1&=u_2=...=u_n=0 &\mbox{ on }\partial\Omega. \end{align*} Here $\Delta$ is the Laplacian operator, $ \lambda$ is a non-negative parameter, $\Omega$ is a bounded domain in $\mathbb R^N$ with smooth boundary $\partial\Omega$ and $f_i\in C^1([0,\infty)),$ $i\in\{1,2,\dots,n\},$ belongs to a class of strictly increasing functions that have a combined sublinear effect at $\infty$. We establish results for positone systems ($f_i(0)\geq0,$ $ i\in\{1,\dots,l-1,l+1,\dots,n\}$ and $f_l(0)>0$ for some $l\in\{1,\dots,n\}$), semipositone systems (no sign conditions on $f_i(0)$) and for systems with $f_i(0)=0,$ $ i\in\{1,2,\dots,n\}.$ We establish our results by the method of sub and supersolutions.

#### Article information

**Source**

Differential Integral Equations, Volume 24, Number 3/4 (2011), 307-324.

**Dates**

First available in Project Euclid: 20 December 2012

**Permanent link to this document**

https://projecteuclid.org/euclid.die/1356019034

**Mathematical Reviews number (MathSciNet)**

MR2757462

**Zentralblatt MATH identifier**

1240.35152

**Subjects**

Primary: 35J55 35J70: Degenerate elliptic equations

#### Citation

Ali, Jaffar; Brown, Ken; Shivaji, R. Positive solutions for $n\times n$ elliptic systems with combined nonlinear effects. Differential Integral Equations 24 (2011), no. 3/4, 307--324. https://projecteuclid.org/euclid.die/1356019034