内容简介：If you think about it, pi is really weird. This irrational number shows up in the craziest places. If you swing a mass back and forth on string,Of course, most people associate pi with circles. That's understandable, since the most basic definition of pi i
If you think about it, pi is really weird. This irrational number shows up in the craziest places. If you swing a mass back and forth on string, there's a pi in there . It pops up in the Heisenberg uncertainty principle , Einstein's general relativity, and the interaction between two electric charges.
Of course, most people associate pi with circles. That's understandable, since the most basic definition of pi is the ratio of the circumference to the diameter of a circle:
Now for the important part. Tomorrow, as you may know, is Pi Day. Why tomorrow? Because it’s March 14—yes, 3/14—and 3.14 is the value of pi to two decimals. Of course, the actual number continues to an infinite number of decimal places: 3.14159265359 … and so on forever. That’s why it’s called irrational.
I should add that the US is pretty much the only place that uses the middle-endian date format of month/day/year. If you go with the little-endian format of day/month/year, then today is 14/3—which is obviously not pi. (In that case I suggest July 22, since the fraction 7/22 is a fairly decent approximation for pi.)
Anyway, my traditional way of celebrating Pi Day is to find a new way each year of calculating a numerical value for pi. It's just what I do. I've been at this for quite some time now, so here are some of my favorites:
- Finding piusing random numbers (and Python)
- Determining the value of pi using a mass oscillating on a spring
- Actually measuring the circumference and diameter of real circles
I have even more Pi Day posts here . But now let's try this a new way. Let’s see how close we can get to pi by drawing a circle.
Here's how this will work. You draw a circle. From that circle, you can determine both the circumference and the radius. Then the value of pi would be the circumference divided by twice the radius. Simple, right?
Oh, but what if your circle isn't perfect? I mean, who draws perfect circles anyway? Let's imagine that this un-perfect circle is actually a bunch of discrete points connected by line segments. If you zoomed on a part of it, it might look like this:
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算法设计与分析基础
Anany levitin / 潘彦 / 清华大学出版社 / 2007-1-1 / 49.00元
作者基于丰富的教学经验，开发了一套对算法进行分类的新方法。这套方法站在通用问题求解策略的高度，能对现有的大多数算法都能进行准确分类，从而使本书的读者能够沿着一条清晰的、一致的、连贯的思路来探索算法设计与分析这一迷人领域。本书作为第2版，相对第1版增加了新的习题，还增加了“迭代改进”一章，使得原来的分类方法更加完善。 本书十分适合作为算法设计和分析的基础教材，也适合任何有兴趣探究算法奥秘的读者......一起来看看 《算法设计与分析基础》 这本书的介绍吧!
