Eigenfunction of an absolutely one-homogeneous functional
= Eigenfunction of an absolutely one-homogeneous functional
{title2=$\lambda f\in\partial J(f)$}
A nonzero vector $f$ is an eigenfunction of an absolutely one-homogeneous convex functional $J$ with eigenvalue $\lambda$ when $\lambda f\in\partial J(f)$. This nonlinear analogue of an <eigenvector> underlies exact shrinkage formulas for several variational flows and proximal maps.