The answer for vectors uses the theory of multi-symmetric polynomials and in particular power sums. You can learn about that in Emmanuel Briand's thesis mentioned in myprevious MO answer Generalizing the Fundamental Theorem of Symmetric PolynomialsGeneralizing the Fundamental Theorem of Symmetric Polynomials Often people attibute the theory to Weyl (in his book on classical groups), however it is much older, with major contributions by Poisson, Schlaffli and Junker.