function f = freq2d(echant,bornex,borney) 
//      freq2d retourne une matrice dont les
//      coefficients sont les frequences de echant
//      relatives a bornex et borney

kx = length(bornex)-1;
ky = length(borney)-1;

for i=1:kx,
    for j=1:ky,
        f(i,j) = length(find(..
            echant(1,:) >  bornex(i)   &..
            echant(1,:) <= bornex(i+1) &..
            echant(2,:) >  borney(j)   &..
            echant(2,:) <= borney(j+1)));
   end;
end;
f=f/sum(f);

























