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