gendata(nbpts, outliers)

          function [x,y] = gendata(nbpts, outliers)
          %GENDATA function [x,y] = gendata(nbpts, outliers)
          %  gnration de donnes y = ax+b + points aberrants
          %  nbpts nombre total de points             (30 par dfaut)
          %  outliers pourcentage de points aberrants (1/3 par dfaut)

          if nargin == 0
            nbpts = 30; outliers = 1/3;
          elseif nargin == 1
            outliers = 1/3;
          end;         
          x = sort(rand(1,fix(nbpts*(1-outliers))));
          a = tan(pi*(rand(1)-0.5));
          b = (rand-0.5);
          y = a.*(x+0.01.*randn(size(x)))+b;
          ymin = min(y);
          ymax = max(y);

          %gnration des points aberrants (outliers) :
          x1 = rand(1,nbpts-length(x));
          y1 = ymin+rand(size(x))*(ymax-ymin);

          % ajout aux prcdents
          [x, i] = sort([x x1]);
          y = [y y1];
          y = y(i);