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Anna Torstensson: Describing subalgebras of k[x] by conditions

Time: Mon 2022-11-28 15.00 - 16.00

Location: Zoom

Video link: Meeting ID: 642 5442 0032

Participating: Anna Torstensson, Lund


Subalgebras of the polynomial ring (in one or several variables) are most commonly described by a set of generators. If we are lucky it is given by generators that form a so called SAGBI basis. A SAGBI basis gives a more direct description of the leading terms occurring in the subalgebra, which in turn makes way for an algorithm for checking if a certain polynomial belongs to the subalgebra.
In this talk we will examine an alternative way to describe subalgebras (that are of finite codimension) in k[x]. This description involves only values of a polynomial and its (directional) derivatives in a finite number of points. It therefore gives a very direct and fast way to check subalgebra membership. We will see examples in one and several variables and discuss some advantages of this way of looking at subalgebras. I will also give you some insight into the ideas of the proof that such a description exists for all subalgebras of finite codimension in k[x].
Finally I will point to some (of the many) related open questions.
Main reference: Subalgebras in K[x] of small codimension Rode Grönkvist, Erik Leffler, Anna Torstensson & Victor Ufnarovski in Applicable Algebra in Engineering, Communication and Computing (2022)
(Can be found here: )