Subalgebra Analogue to Standard Basis for Ideal

Abstract

The theory of "subalgebra basis" analogous to standard basis (the generalization of Gr\"{o}bner bases to monomial ordering which are not necessarily well ordering \cite{GP1}.) for ideals in polynomial rings over a field is developed. We call these bases "SASBI Basis" for "Subalgebra Analogue to Standard Basis for Ideals". The case of global orderings, here they are called "SAGBI Basis" for "Subalgebra Analogue to Gr\"{o}bner Basis for Ideals", is treated in \cite{RS1}. Sasbi bases may be infinite. In this paper we consider subalgebras admitting a finite Sasbi basis and give algorithms to compute them. The algorithms have been implemented as a library for the computer algebra system SINGULAR \cite{GPS1}.