Total $\mathbb{A}$-variation-type flows for general integrands

Abstract: We study the $L^2$-gradient flows for functionals of the type $\int_{\Omega}f(x,\mathbb{A}u)\,\mathrm{dx}$, where $f$ is a convex function of linear growth and $\mathbb{A}$ is some first-order linear constant-coefficient differential operator. To this end we identify the relaxation of the functional to the space $\mathrm{BV}^{\mathbb{A}}\cap L^2$, identify its subdifferential, and show pointwise representation formulas for the relaxation and the subdifferential, both with and without Dirichlet boundary conditions. The existence and uniqueness then follow from abstract semigroup theory. Another main novelty of our work is that we require no regularity or continuity assumptions for $f$.