Submitted on: 30 April 2011.
Revised on: 17 August 2011.
Accepted on: 11 September 2011.
___________________IMA Journal of Management Mathematics
Submitted on: 14 June 2008.
Revised on: 15 July 2008.
Accepted on: 02 September 2008.
___________________IMA Journal of Management Mathematics
Submitted on: 28 January 2002.
Revised on: 26 May 2002.
Accepted on: 27 June 2002.
___________________IMA Journal of Management Mathematics
http://reply.papertrans.cn/2/123/12241/12241-34.png
http://reply.papertrans.cn/2/123/12241/12241-35.png
http://reply.papertrans.cn/2/123/12241/12241-36.png