According to the theory proposed by Acerbi and Scandolo (2008) [<italic>Quant. Finance</italic>, 2008, <bold>8</bold>, 681--692], an asset is described by the so-called Marginal Supply--Demand Curve (MSDC), which is a collection of bid and ask prices according to its trading volumes, and the value of a portfolio is defined...

The present situation, problems and constraints of the circular agriculture development in Hebei Province are systematically analyzed，the subject modes suitable for the development of circular agriculture and the value-added potential are described, and finally some proposals are put forward.