T. Blass, R. de la Llave, E. Valdinoci
A Comparison Principle for a Sobolev Gradient Semi-Flow
(527K, Ps)

ABSTRACT.  We consider gradient descent equations for energy functionals of 
the type $S(u) = \frac{1}{2}\langle u(x), A(x)u(x) \rangle_{L^2} + 
\int_{\Omega} V(x,u) \, dx$, where $A$ is a 
uniformly elliptic operator of order 2, with smooth coefficients.
The gradient descent equation for such a functional depends on the
metric under consideration. 
We consider the steepest descent equation
for $S$  where the gradient is an element of the Sobolev space
$H^{\beta}$, $\beta \in (0,1)$, with a metric that depends on $A$ 
and a positive number $\gamma > \sup |V_{22}|$. 
We prove a weak comparison principle for such a gradient flow.
We extend our methods to the case where $A$ is a fractional power of
an elliptic operator. 
We provide an application to the Aubry-Mather theory for partial
differential equations and pseudo-differential equations.