code: def  dBinaryRochedz(r, D, q, F):
      
      return -r[2]*(r[0]*r[0]+r[1]*r[1]+r[2]*r[2])**-1.5 -q*r[2]*((r[0]-D)*(r[0]-D)+r[1]*r[1]+r[2]*r[2])**-1.5
docs: Computes a derivative of the potential with respect to z.
  
      @param r:      relative radius vector (3 components)
      @param D:      instantaneous separation
      @param q:      mass ratio
      @param F:      synchronicity parameter