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