March 2020
Intermediate to advanced
200 pages
3h 12m
Chinese
Content preview from 复杂性思考：复杂性科学和计算模型（原书第2 版）
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元胞自动机
｜
71
直线。另一些在空间中平移，表现为具有不同斜率的对角线，这取决于它们
移动一列的时间步长。这些结构被称为
宇宙飞船
。
图 5-5：规则 110 从随机初始条件开始和 600 个时间步长后的结果
宇宙飞船之间的碰撞会产生不同的结果，这取决于宇宙飞船的类型以及它们
碰撞时所处的阶段。有些碰撞使两艘飞船都毁灭了，其他飞船保持不变，还
有一些生产一艘或多艘不同类型的飞船。
这些碰撞是 CA 规则 110 中计算的基础。如果你将宇宙飞船看作在太空中传
播的信号，把碰撞看作计算诸如 AND（与） 和 OR（或）之类逻辑运算的门，
你就会明白 CA 执行计算意味着什么。
5.7 普遍性
为了理解普遍性，我们必须理解可计算性理论，这是关于计算模型及其计算
内容的理论。
图灵机是最常用的计算模型之一，它是阿兰
·
图灵在 1936 年提出的一种抽象
计算机。图灵机是一个一维的 CA，在两个方向上都是无限的，并带有一个读
写头。在任何时候，头部都是位于单个单元格之上。它可以读取该单元格的
状态（通常只有两种状态），并可以将一个新值写入该单元格。
此外，该机器还有一个寄存器，它记录机器的状态（有限状态之一）和一张规
则表。对于每个机器状态和单元格状态，该表指定一个操作。动作包括修改
头部上方的元胞，并将一个元胞向左或向右移动。
72
｜
第
5
章
图灵机不是计算机的实用设计，而是对常见的计算机体系结构进行建模。对
于在实际计算机上运行的给定程序，构造一台执行等效计算的图灵机是可能
的（至少在原则上是可能的）。
图灵机很有用，因为它可以刻画一组图灵机可以计算的一组函数 ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.