The present paper gives a classification of the expressive power of two-variable least fixed-point logics. The main results are: 1. The two-variable fragment of monadic least fixed-point logic with parameters is as expressive as full monadic least fixed-point logic (on binary structures). 2. The two-variable fragment of monadic least fixed-point logic without parameters is as expressive as the ...

In order to achieve the best filtering performance and make the filter automatically adjust its coefficients with the changing of its working environment, we need to use adaptive filter technique. To overcome the contradiction of traditional LMS algorithm between convergence speed, convergence accuracy and the selection of step-size, a novel variable step-size & variable parameters adaptive fil...