     const std::vector<container>& potential( ) const { return phi;}
     void initializene( const container& y, container& target);
 
-    void operator()( std::vector<container>& y, std::vector<container>& yp);
+    void operator()( const std::vector<container>& y, std::vector<container>& yp);
 
     double mass( ) {return mass_;}
     double mass_diffusion( ) {return diff_;}

        LaplacianM_perp_phi ( g,p.bc_x_phi,g.bcy(), dg::normed, dg::centered)
    {
    }
    void operator()( std::vector<container>& x, std::vector<container>& y)
    {
        /* x[0] := N_e - (bgamp+profamp)
           x[1] := N_i - (bgamp+profamp)

    }
    dg::Elliptic<Geometry, Matrix, container>& laplacianM() {return LaplacianM_perp_phi;}
    const container& weights(){return LaplacianM_perp.weights();}
    const container& inv_weights(){return LaplacianM_perp.inv_weights();}
    const container& precond(){return LaplacianM_perp.precond();}
  private:
    const eule::Parameters p;
