Gradient flows in Hilbert spaces: Difference between revisions
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<!-- '''Gradient Flows in Hilbert Spaces''' are generalizations of time-derivatives with a gradient constraint. Specifically, a gradient flow is a Hilbert Space valued function who's time derivative lies in some generalized collection of gradient vectors. Gradient flows are a key topic in the study of non-linear time evolution partial differential equations. !--> | <!-- '''Gradient Flows in Hilbert Spaces''' are generalizations of time-derivatives with a gradient constraint. Specifically, a gradient flow is a Hilbert Space valued function who's time derivative lies in some generalized collection of gradient vectors. Gradient flows are a key topic in the study of non-linear time evolution partial differential equations. !--> | ||
<!-- ==Introduction== --!> | <!-- ==Introduction== The heat equation is a classic example of a time evolution partial differential equation. In particular, the heat equation is a linear parabolic partial differential equation. Such PDEs are well understood and are solvable using several different approaches. One particularly interesting technique is to view the PDE as a Banach-space valued ODE in the time variable. In this case, we can try to understand how to write the solution of the PDE as a flow in time which is a generalization of the exponential function. The techniques which one implements to find such a solution ultimately result in the Hille-Yosida theorem, which gives necessary and sufficient conditions for the operator T to be infinitesimal generator of a contraction semigroup of the given PDE. In some sense, these ideas can be extended to non-linear time evolution PDEs, leading to the general notion of flows on Hilbert spaces. We will discuss in this article how the theory of flows can be used to yield existence of a solution of a "non-linear heat equation." --!> | ||
<!-- ==References== <ref>Ambrosio, Brue, Semola; Lectures on Optimal Transport</ref>, <ref>Evans; PDEs</ref>--!> | <!-- ==References== <ref>Ambrosio, Brue, Semola; Lectures on Optimal Transport</ref>, <ref>Evans; PDEs</ref>--!> | ||
Revision as of 21:31, 7 February 2022
Editing in progress. Edits will be rendered when the draft is complete.