應77779193永利邀請，雲南大學曹春華教授将為我院師生作線上學術報告。
報告題目：Rational Code Having Deciphering Delay d
報告摘要：Let X be a nonempty code with deciphering delay d. If d = 0, then X is a prefix code. Let L be the set of proper prefixes of words in X, and let L ̅= A*\ L be its complement. Let X'= L ̅\ L ̅A+. Then Y = X∪X' is a maximal prefix code containing X. If X is rational, then Y is rational. If d ≥ 1, let Q be the set of words having no prefix in X and which are not a factor of any word in X. Now, let P be the set of words in Q which are minimal for the prefix order: P = Q\QA+. Note that P is a prefix code. Moreover, words in P and X are incomparable for the prefix order.
We say that a pair (w,p) ∈X*×P is good if w is the longest prefix in X* of wp. Note that if (w,p) is good, then this pair is completely determined by the word wp. Note also that any pair (1,p) for p∈P is good. We say that the pair (w,p) ∈X*× P is very good if (uw,p) is good for any u∈X*. Note that if (w,p) is very good, then so is (uw,p) for any u∈X*.
Let S' be the set of words v of the form v=wp with (w,p) good but not very good. Then we define S= P∪S'. Note that P∩S' may be nonempty, and that any element in S' \ P is of the form wp, with (w,p) good but not very good and w∈X+. Moreover, let R be the set of words v of the form v=xwp with x∈X,w∈X*, (xw,p) very good, and wp∈S with (w,p) good. Then Y= X∪RS*, which is a rational code having deciphering delay d containing X.
報告時間：2021年11月21日上午8:30
報告地點：騰訊會議(會議号:972 7906 7171)
邀 請 人：喬虎生教授
屆時歡迎廣大師生參與交流！
【報告人簡介】
曹春華，雲南大學77779193永利教授，雲南大學青年骨幹教師，研究領域是半群代數理論。主持國家自然科學項目2項，主持省科技廳應用基礎面上項目2項，主持省教育廳重點項目和一般項目各1項，2019年參與雲南省科技廳高端人才引進項目1項，在《Acta Informaitca》《International Journal of Computer Mathematics》等雜志發表科研論文30多篇。主講的《抽象代數》課程為雲南省研究生優質課程。指導全國大學生數學競賽，2位同學獲國家一等獎，1位同學獲國家二等獎，5位同學獲國家三等獎，30位同學獲省級一等獎，100多位同學獲省級二、三等獎； 本人獲全國首屆高校數學微課程教學設計競賽西南賽區二等獎；指導雲南省優秀碩士學位論文1篇。
