在metrics中不支持常量,但是可以用下面的办法实现
engine = createReactiveStateEngine(name="test", metrics=[<mavg(price, 3)>, <price-price+1>], dummyTable=trade, outputTable=outputTable, keyColumn=["date","sym"], filter=<date between 2012.01.01 : 2012.01.03>, keepOrder=true)