Difference equation for the Heckman-Opdam hypergeometric function and   its confluent Whittaker limit
  We present an explicit difference equation for the Heckman-Opdam hypergeometric function associated with root systems. Via a confluent hypergeometric limit, an analogous difference equation is obtained for the class-one Whittaker function diagonalizing the open quantum Toda chain. 
J.F. van Diejen and E. Emsiz
math.RT math-ph math.MP