Functions with a unique mean value and amenability

Invariant Mean Value Property and Harmonic Functions

We give conditions on the functions σ and u on R such that if u is given by the convolution of σ and u, then u is harmonic on R.

A Generalized Mean Value Inequality for Subharmonic Functions and Applications

If u ≥ 0 is subharmonic on a domain Ω in Rn and p > 0, then it is well-known that there is a constant C(n, p) ≥ 1 such that u(x)p ≤C(n, p)M V (up,B(x,r)) for each ball B(x,r) ⊂ Ω. We recently showed that a similar result holds more generally for functions of the form ψ◦ u where ψ : R+ → R+ may be any surjective, concave function whose inverse ψ−1 satisfies the ∆2-condition. Now we point out tha...

Harmonic functions via restricted mean-value theorems

Let f be a function on a bounded domain Ω ⊆ R and δ be a positive function on Ω such that B(x, δ(x)) ⊆ Ω. Let σ(f)(x) be the average of f over the ball B(x, δ(x)). The restricted mean-value theorems discuss the conditions on f, δ, and Ω under which σ(f) = f implies that f is harmonic. In this paper, we study the stability of harmonic functions with respect to the map σ. One expects that, in gen...

A note on unique solvability of the absolute value equation

It is proved that applying sufficient regularity conditions to the interval matrix $[A-|B|,A + |B|]$, we can create a new unique solvability condition for the absolute value equation $Ax + B|x|=b$, since regularity of interval matrices implies unique solvability of their corresponding absolute value equation. This condition is formulated in terms of positive deniteness of a certain point matrix...

Triangular approximations of fuzzy number with value and ambiguity functions