1. A computer-implemented state filter comprising receiving, using a computer, a multivariate data set; receiving, using the computer, information about a particular signal state, wherein said information is represented by a state vector of interest; generating, using the computer, a set of orthonormal vectors from the multivariate data set that contains the state vector of interest; constructing, using the computer, a generalized set of matrices based upon the set of orthonormal vectors, that are trace-orthogonal and which serve as a basis set for expansion of a spectral matrix; forming, using the computer, a generalized Stokes vector from coefficients of the expansion, wherein the generalized Stokes vector that represents power in the spectral matrix associated with the state vector of interest; and constructing, using the computer, filters that serve to extract or suppress information about a particular state using components of the generalized Stokes vector.