Necessary and Sufficient Conditions for the Schur Harmonic Convexity or Concavity of the Extended Mean Values

In this paper, we prove that the extended values E(r, s;x, y) are Schur harmonic convex (or concave, respectively) with respect to (x, y) ∈ (0,∞) × (0,∞) if and only if (r, s) ∈ {(r, s) : s ≥ −1, s ≥ r, s+ r + 3 ≥ 0} ∪ {(r, s) : r ≥ −1, r ≥ s, s+r+3 ≥ 0} (or {(r, s) : s ≤ −1, r ≤ −1, s+r+3 ≤ 0}, respectively).