Symmetric Circuits for Rank Logic

Abstract

Fixed-point logic with rank (FPR) is an extension of fixed-point logic with counting (FPC) with operators for computing the rank of a matrix over a finit field. The expressive power of FPR properly extends that of FPC and is contained in P, but it is not known if that containment is proper. We give a circuit characterization for FPR in terms of families of symmetric circuits with rank gates, along the lines of that for FPC given by Anderson and Dawar in 2017. This requires the development of a broad framework of circuits in which the individual gates compute functions that are not symmetric (i.e., invariant under all permutations of their inputs). This framework also necessitates the development of novel techniques to prove the equivalence of circuits and logic. Both the framework and the techniques are of greater generality than the main result.

Symmetric Arithmetic Circuits

“…In particular, the majority function is not computable by any family of polynomial-size symmetric circuits over B std . On the other hand, it is also known [12] that adding any fully symmetric functions to the basis does not take us beyond the power of B t . Thus, the threshold basis B t gives the robust notion, and that is what we use here.…”