Symmetric and r-Symmetric Tropical Polynomials and Rational Functions
  A tropical polynomial in nr variables divided into blocks of r variables each, is r-symmetric, if it is invariant under the action of Sn that permutes the blocks. For r=1 we call these tropical polynomials symmetric. We can define r-symmetric and symmetric rational functions in a similar manner. In this paper we identify generators for the sets of symmetric tropical polynomials and rational functions. While r-symmetric tropical polynomials are not finitely generated, we show that r-symmetric rational functions are and provide a list of generators. 
Sara Kalisnik Verovsek and Gunnar Carlsson
math.RA