function poly=lagrange(X,Y)
   N=length(X);
   poly=zeros(N,1);
   for h=1:N
     polytmp=1;
     for k=1:N
         if(h~=k)
            polytmp=poly_mul(polytmp,[-X(k);1]./(X(h)-X(k))); 
         end;
     end;
      polytmp=poly_mul(Y(h),polytmp);   
      poly=poly_add(poly,polytmp); 
   end;