
 Presentation of Modal Interval Analysis 
  From an interval point of view the common alternative of computing with single numbers is able to provide only an indication of the true result that could be reached using interval calculus: only a single value pointing somewhere inside the complete interval result. 
  For a rational function f(x1,...,xn) a rational interval extension fR(X1,...,Xn) is defined through the sintactic tree of f, with their numerical arguments x1,...,xn replaced by the interval arguments X1,...,Xn and with the numerical operations of f replaced by their corresponding interval operations, which in case of approximate computations must be externally rounded. 
  where the "intervals" [2,1] and [6,3] are the dual of the intervals [1,2] and [3,6]. 
 ima.udg.es /SIGLA/X/mod_interval (1326 words) 
