centration intensity matrix; e) unweighting the matrix S generated in step d) by applying the inverse of the weighting used in step b); f) estimating the spectral background B; g) calculating P=S???B and SB=B, and redefine S=[P SB], where P is a matrix of pure spectral components without background; h) reweighting S and B, using the same weighting that was used in step b); i) solving D=[CP CB]???[