Stable linear fractional transformations with applications to stabilization and multistage H∞ control design

New calcium and magnesium complexes of phytohemagglutinin-polyheteroglycans are distinguished inter alia by cytoprotective, antiinflammatory and immunostimulating properties. They have characteristic molecular weights and distribution thereof, infrared spectra and compositions in respect of calcium and/or magnesium, phosphorus, glycans and amino acids. The preparation is carried out by extraction of the phytohemagglutinin-polyglycans with water of weakly alkaline pH from plants, in particular of the families Compositae, Malvaceae, Cucurbitaceae and Gramineae, and precipitation with an alcohol which is miscible with water. The complexes can be used for the treatment of ulcers, inflammations or viral infections, or as immunostimulant.