On Λ-fractional variational calculus

Pointing out that Λ-fractional analysis is the unique fractional calculus theory including mathematically acceptable derivatives, variational for established. Since a non-local procedure, global extremals are only accepted. That means should satisfy not Euler–Lagrange equation but also additional Weierstrass-Erdmann corner conditions. Hence stability criteria introduced. The proposed procedure applied to any branch of physics, mechanics, biomechanics, etc. present refraction light.