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moocs-coursera-automata-note2/ #35

Open kkdai opened 3 years ago

kkdai commented 3 years ago

[Coursera][Automata] 自動機理論-Automata筆記-第二週: Regular Expression

http://www.evanlin.com/moocs-coursera-automata-note2/

kkdai commented 3 years ago

comment written by Dboy Liao, created at 03 Oct 15 05:40 UTC,

我其實一直想不通的是 RE, symbol 跟 string 的差別~
或者說~
我現在的理解就是 string 是由 symbol 組成的~
但是 RE 呢?
它不是 string 的話那是什麼?

kkdai commented 3 years ago

comment written by Dboy Liao, created at 03 Oct 15 05:48 UTC,

剛 po 完就想到~
或許我們可以把 RE 想成一個 DFA 的 string 表示法~
所以本質上是 string ~
但它代表一個 DFA ~

kkdai commented 3 years ago

comment written by Evan Lin, created at 03 Oct 15 06:27 UTC,

一個DFA代表的是一個language ，而RE只是拿來敘述這個語言的表示式． 之後會提到Regular Language(代表該語言可以用RE表示）

DFA是唯一能夠轉換成RE來表示的方法．

String 只是所有被該DFA接受的字串 (符合RE)

ex: RE = { 0* 1+} 他的字串可以是 {1, 01, 000111 ...}

kkdai commented 3 years ago

comment written by Dboy Liao, created at 03 Oct 15 07:05 UTC,

哈~
我晚一個禮拜開始果然有差~
現在快追上進度了~
Thx ~

kkdai commented 3 years ago

comment written by hua eliza, created at 26 Feb 17 03:01 UTC,

string在pumping theory 裡面必須是long string ( cardinality of the string must longer than the number of state of the machine )