Positivity for large time of solutions of the heat equation: the parabolic antimaximum principle
Jesus Ildefonso Díaz - Dpto. Matemática Aplicada, Univ. Complutense, 28040 Madrid, Spain (email)
Abstract: We study the positivity, for large time, of the solutions to the heat equation $\mathcal Q_a(f,u^0)$:
$\mathcal Q_a(f,u^0)\qquad$ $\partial_tu-\Delta u=au+f(t,x),$ in $Q=]0,\infty [ \times \Omega, $
$u(t,x)=0\qquad$ $(t,x)\in ]0,\infty [ \times \partial \Omega,$
$u(0,x)=u^0(x), \qquad x\in \Omega,$
where $\Omega$ is a smooth bounded domain in $\mathbb R^N$ and $a\in\mathbb R$. We obtain some sufficient conditions for having a finite time $t_p>0$ (depending on $a$ and on the data $u^0$ and $f$ which are not necessarily of the same sign) such that $ u(t,x)>0 \forall t>t_p, a. e. x\in\Omega$.
Keywords: Maximum and antimaximum principle, heat equation, parabolic problems.
Received: March 2003; Revised: August 2003; Published: October 2003.
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