dichot(t, x);

           function i = dichot(t, x);

           beg =  1;
           fin =  length(t);
           while 1
             mil =  (beg+fin)/2;
             if t(mil) >  x
               beg =  mil+1;
             elseif t(mil) < x
               fin =  mil-1; 
             else
               i =  mil;
               break; 
             end;
             if beg > fin
               i =  0;      
               break;
             end; 
           end;