Abstract. Let R be a commutative ring with identity, I(X, R) be the incidence algebra of a locally finite pre-ordered set X. In this note, we characterise the derivations of I(X, R) and prove that every Jordan derivation of I(X, R) is a derivation provided that R is 2-torsion free.
IntroductionLet R be a commutative ring with identity, A be an algebra over R. An Rlinear mapping D : A → A is called a derivation if D(xy) = D(x)y + xD(y) for all x, y ∈ A, and is called a Jordan derivation iffor all x ∈ A. There has been a great interest in the study of Jordan derivations of various algebras in the last decades. The standard problem is to find out whether a Jordan derivation degenerate to a derivation. Jacobson and Rickart [8] proved that every Jordan derivation of the full matrix algebra over a 2-torsion free unital ring is a derivation by relating the problem to the decomposition of Jordan homomorphisms. In [7], Herstein showed that every Jordan derivation from a 2-torsion free prime ring into itself is also a derivation. These results have been extended to different rings and algebras in various directions (see [2,3,6,11,20] and the references therein). We would like to refer the reader to Brešar's paper [4] for a comprehensive and more detailed understanding of this topic. We now recall the definition of incidence algebras. Let (X, ) be a locally finite pre-ordered set. This means is a reflexive and transitive binary relation on the set X, and for any x y in X there are only finitely many elements z satisfying x z y. The incidence algebra I(X, R) of X over R is defined on the setwith algebraic operation given byfor all f, g ∈ I(X, R), r ∈ R and x, y, z ∈ X. The product (f g) is usually called convolution in function theory. It would be helpful to point out that the full matrix 2010 Mathematics Subject Classification. 16W10, 16W25, 47L35.