Hasse–Schmidt derivation

In mathematics, a Hasse–Schmidt derivation is an extension of the notion of a derivation. The concept was introduced by Schmidt & Hasse (1937).

Definition

For a (not necessarily commutative nor associative)

A, a Hasse–Schmidt derivation is a map of B-algebras

${\displaystyle D:A\to A[\![t]\!]}$

taking values in the ring of formal power series with coefficients in A. This definition is found in several places, such as Gatto & Salehyan (2016, §3.4), which also contains the following example: for A being the ring of infinitely differentiable functions (defined on, say, Rⁿ) and B=R, the map

${\displaystyle f\mapsto \exp \left(t{\frac {d}{dx}}\right)f(x)=f+t{\frac {df}{dx}}+{\frac {t^{2}}{2}}{\frac {d^{2}f}{dx^{2}}}+\cdots }$

is a Hasse–Schmidt derivation, as follows from applying the Leibniz rule iteratedly.

Equivalent characterizations

Hazewinkel (2012) shows that a Hasse–Schmidt derivation is equivalent to an action of the bialgebra

${\displaystyle \operatorname {NSymm} =\mathbf {Z} \langle Z_{1},Z_{2},\ldots \rangle }$

of noncommutative symmetric functions in countably many variables Z₁, Z₂, ...: the part ${\displaystyle D_{i}:A\to A}$ of D which picks the coefficient of ${\displaystyle t^{i}}$, is the action of the indeterminate Z_i.

Applications

Hasse–Schmidt derivations on the exterior algebra ${\textstyle A=\bigwedge M}$ of some B-module M have been studied by Gatto & Salehyan (2016, §4). Basic properties of derivations in this context lead to a conceptual proof of the Cayley–Hamilton theorem. See also Gatto & Scherbak (2015).

References

• Gatto, Letterio; Salehyan, Parham (2016), Hasse–Schmidt derivations on Grassmann algebras, Springer,
  MR 3524604
• Gatto, Letterio; Scherbak, Inna (2015), Remarks on the Cayley-Hamilton Theorem,
  arXiv:1510.03022
• Hazewinkel, Michiel (2012), "Hasse–Schmidt Derivations and the Hopf Algebra of Non-Commutative Symmetric Functions", Axioms, 1 (2): 149–154,
  S2CID 15969581
• Schmidt, F.K.;
  S2CID 120317012