classify:= H -> if linalg[definite](H, positive_def) then 'loc_min'
                elif linalg[definite](H, negative_def) then 'loc_max'
                elif linalg[definite](H, positive_semidef)
                  or linalg[definite](H, negative_semidef) then 'uncertain'
                else 'saddle' fi;
