上下文无关文法（Context-Free Grammar, CFG）是一个4元组G=(V, T, S, P)，其中，V和T是不相交的有限集，S∈V，P是一组有限的产生式规则集，形如A→α，其中A∈V，且α∈(V∪T)*。V的元素称为非终结符，T的元素称为终结符，S是一个特殊的非终结符，称为文法开始符。 设G=(V, T, S, P)是一个CFG，则G产生的语言是所有可由G产生的字符串组成的集合，即L(G)={x∈T* | Sx}。一个语言L是上下文无关语言（Context-Free Language, CFL），当且仅当存在一个CFG G，使得L=L(G)。 *⇒ 例如，设文法G：S→AB A→aA|a B→bB|b 则L(G)={a^nb^m | n,m>=1} 其中非终结符都是大写字母，开始符都是S，终结符都是小写字母。
标签： Context-Free Grammar CFG
上传时间： 2013-12-10
上传用户：gaojiao1999
There is an example of how to use the LDPC encode/decode with AWGN channel model in files .\ldpc_decode.m and .\GFq\ldpc_decode.m. There are a few parity check matrices available in the code but you can use other matrices provided you have enough memory to load them. I suggest checking out matrices in Alist format available on David MacKay s web site.You will need to have access to a MEX compiler to be able to use a few functions written in C. LDPC的仿真代码
标签： example channel ldpc_de encode
上传时间： 2013-12-03
上传用户：lili123
Problem Statement You are given a string input. You are to find the longest substring of input such that the reversal of the substring is also a substring of input. In case of a tie, return the string that occurs earliest in input. Definition Class: ReverseSubstring Method: findReversed Parameters: string Returns: string Method signature: string findReversed(string input) (be sure your method is public) Notes The substring and its reversal may overlap partially or completely. The entire original string is itself a valid substring (see example 4). Constraints input will contain between 1 and 50 characters, inclusive. Each character of input will be an uppercase letter ( A - Z ). Examples 0) "XBCDEFYWFEDCBZ" Returns: "BCDEF" We see that the reverse of BCDEF is FEDCB, which appears later in the string. 1)
上传时间： 2015-09-21
上传用户：sunjet
In the process of copper flash smelting, lining temperature of reaction shaft and its inner wall sluggish play a very important role in lining life. Up to now, however
标签： temperature smelting reaction process
上传时间： 2015-10-03
上传用户：wang5829
C#中实现最短路，该图算法描述的是这样的场景：图由节点和带有方向的边构成，每条边都有相应的权值，路径规划（最短路径）算法就是要找出从节点A到节点B的累积权值最小的路径。
标签： 短路
上传时间： 2014-01-12
上传用户：sammi
his paper provides a tutorial and survey of methods for parameterizing surfaces with a view to applications in geometric modelling and computer graphics. We gather various concepts from di® erential geometry which are relevant to surface mapping and use them to understand the strengths and weaknesses of the many methods for parameterizing piecewise linear surfaces and their relationship to one another.
标签： parameterizing provides tutorial surfaces
上传时间： 2014-11-09
上传用户：努力努力再努力
How well do you really know Java? Are you a code sleuth? Have you ever spent days chasing a bug caused by a trap or pitfall in Java or its libraries? Do you like brainteasers? Then this is the book for you!
上传时间： 2013-11-25
上传用户：王庆才
A one-dimensional calibration object consists of three or more collinear points with known relative positions. It is generally believed that a camera can be calibrated only when a 1D calibration object is in planar motion or rotates around a ¯ xed point. In this paper, it is proved that when a multi-camera is observing a 1D object undergoing general rigid motions synchronously, the camera set can be linearly calibrated. A linear algorithm for the camera set calibration is proposed，and then the linear estimation is further re¯ ned using the maximum likelihood criteria. The simulated and real image experiments show that the proposed algorithm is valid and robust.
标签： one-dimensional calibration collinear consists
上传时间： 2014-01-12
上传用户：璇珠官人
一:需求分析 1. 问题描述 魔王总是使用自己的一种非常精练而抽象的语言讲话,没人能听懂,但他的语言是可逐步解释成人能听懂的语言,因为他的语言是由以下两种形式的规则由人的语言逐步抽象上去的: ----------------------------------------------------------- (1) a---> (B1)(B2)....(Bm) (2)[(op1)(p2)...(pn)]---->[o(pn)][o(p(n-1))].....[o(p1)o] ----------------------------------------------------------- 在这两种形式中,从左到右均表示解释.试写一个魔王语言的解释系统,把 他的话解释成人能听得懂的话. 2. 基本要求: 用下述两条具体规则和上述规则形式(2)实现.设大写字母表示魔王语言的词汇 小写字母表示人的语言的词汇 希腊字母表示可以用大写字母或小写字母代换的变量.魔王语言可含人的词汇. (1) B --> tAdA (2) A --> sae 3. 测试数据: B(ehnxgz)B 解释成 tsaedsaeezegexenehetsaedsae若将小写字母与汉字建立下表所示的对应关系,则魔王说的话是:"天上一只鹅地上一只鹅鹅追鹅赶鹅下鹅蛋鹅恨鹅天上一只鹅地上一只鹅". | t | d | s | a | e | z | g | x | n | h | | 天 | 地 | 上 | 一只| 鹅 | 追 | 赶 | 下 | 蛋 | 恨 |
上传时间： 2014-12-02
上传用户：jkhjkh1982
[输入] 图的顶点个数N，图中顶点之间的关系及起点A和终点B [输出] 若A到B无路径，则输出“There is no path” 否则输出A到B路径上个顶点 [存储结构] 图采用邻接矩阵的方式存储。 [算法的基本思想] 采用广度优先搜索的方法，从顶点A开始，依次访问与A邻接的顶点VA1,VA2,...,VAK, 访问遍之后,若没有访问B，则继续访问与VA1邻接的顶点VA11,VA12,...,VA1M，再访问与VA2邻接顶点...，如此下去，直至找到B，最先到达B点的路径，一定是边数最少的路径。实现时采用队列记录被访问过的顶点。每次访问与队头顶点相邻接的顶点，然后将队头顶点从队列中删去。若队空，则说明到不存在通路。在访问顶点过程中，每次把当前顶点的序号作为与其邻接的未访问的顶点的前驱顶点记录下来，以便输出时回溯。 #include<stdio.h> int number //队列类型 typedef struct{ int q[20]
标签： 输入
上传时间： 2015-11-16
上传用户：ma1301115706
