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The idea behind all these algorithms is that what's ultimately important is how many comparisons you ultimately need to make.
这些算法的思想是,你最终需要做多少次的比较,这才是真正重要的。
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And it's pretty expensive to do so because I think they know you need to do it.
这样做很贵，因为我想他们知道你需要这么做。
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And because, of course, we have this carbon here what you end up doing is adding a carbon to your molecule.
因为，当然，我们这里有一个碳,接下来需要做的就是在你的分子中再加上一个碳。
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So the moral here, again, is whenever you're doing an implementation of a simulation, you do need to have some underlying theory about the model.
所以这里的寓意还是,不管你在做什么东西的仿真程序，你需要有一个,模型的底层程序。
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And, that's a good thing to know because if you come out with an answer that's somewhere near the diameter of the universe and it's supposed to be the diameter of an atom, then you will know that you probably made a mistake.
这是我们需要知道的,因为当你做一道题得到的答案,是宇宙的直径,而正确答案是原子直径时，你能很快发现你的错误。
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Exactly, so you might have been thought especially in years past to defragment, so to speak, your hard drive once in a while.
你可能认为需要进行,碎片整理这种操作，也可以说硬盘驱动器有时需要你这么做。
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You just walking.
你所需要做的就是走路。
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And the challenge for scheduling is to pick the things that you want the president to be working on and the president wants to be focusing on proactively rather than just reacting to whatever the crisis on the day was.
安排日程的难处在于,选择事情,选择你要让总统去做,选择总统需要积极投入,而不仅仅是消极回应的,每天发生的大事情。
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You can work as a mechanic, you don't need to have gone to high school.
你能做一名机械师，而你不需要读过高中。
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If you did it in the lab or on your computer screen, you would do it by pushing buttons.
如果你在实验室做，或者在电脑上做，你需要按键。
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The reason you have to get it out of your head is you need to be able to see it on a surface that is not in your mind.
这么做的原因是,你需要,客观地观察它,而不是看它在你大脑中的样子。
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It is true mathematically, you can add two numbers, but you've got to ask yourself,"What am I doing as a physicist when I add these two numbers?"
在数学上它是正确的,你可以引入这两个常数,但是你需要问问自己,当我引入这两个常数时,这么做有什么物理意义
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It's very expensive when you take into account not only the direct costs, but also the costs that you pay advisors to help you make these decisions.
非常昂贵,不仅需要考虑直接成本,还要考虑,支付给帮你做决策的顾问们的费用
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you do whatever you got to do to get what you want.
你得做任何你需要做的去争取你所要的。
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You go through all the work to be a model.
你也准备好了做模特需要的一切功课。
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When you say "it must", this usually does not mean it needs to do something.
当你说“It must”的时候，通常并不表示它需要做某事。
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Occasionally, you'll find you need to cancel out units, because, of course, you're always doing unit analysis as you solve your problems, and sometimes you'll need to convert joules to kilogram meters square per second squared.
偶然地，你会发现需要消除单位，因为在解题时,经常要做单位分析，所以有时候需要把,焦耳换做,一千克乘以米的平方除以秒的平方。
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And you should just do it to learn the material.
如果你没法做需要帮助的话。
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And what that means it's there's all sorts of precautions and procedures you take that are special when you deal with these.
这意味着当你与它们打交道的时候,你需要做各种各样特别的防范措施与流程。
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And we can simplify this expression as saying negative e squared over 4 pi, epsilon nought r squared. Epsilon nought is a constant, it's something you might see in physics as well.
也会遇到它,在这里，你可以就把它,理解为一个转换系数,我们需要做的。
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You won't always draw out every single possibility that you have to start with.
你都可以这样做,大家并不需要每次都把所有可能的结构都写出来。
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- But there's one potential gotcha here -- and this is where you have to be kind -- of piecing together the little clues along the way -- what have I done that's interesting here that had I not, I would have had a mathematical error?
但是这里有一个可能性-,这就是你需要把,一些线索拼凑在一起-,我这里所做的是很有趣的，如果我不这样做，我可能已经犯了个数学错误？
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So what you typically do and a hash case is you design your code to deal with that.
你所需要做的就是通过设计你的代码,来解决上面的问题。
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One of the things we are taught is a verse of Koran, in English it's as "all you who believe, fasting has been prescribed for you as was prescribed for those before you."
在《可兰经》里有一句诗是，大意是，虔诚的人们啊，斋戒不仅是你需要做的,也是你的前人所需要做的“
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This should make sense because if something has a low ionization energy, that means it's not very electronegative, which means it's going to be a lot happier giving up electron density, which is essentially what you're doing -- when you're forming covalent bonds is you're sharing some of your electron density.
这应该是合理的,因为如果某物的电离能很低，这也就意味着它的电负性也不高，那么它就会更愿意,放弃一定的电子密度，而本质上这正是你在,形成共价键时所需要做的,分享你的一些电子密度。
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You really want to get the power of dividing things up, but if you end up doing a ton of work at the combination stage, you may not have gained anything.
你真的想得到分解问题的能力,但是如果在合成的某个阶段,你需要做大量的工作，你可能得不到任何东西。
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It predicts that the best timing is when the conditioned stimulus, which is the signal, comes before the unconditioned stimulus, which is what you have to prepare for.
它预测，最佳的时机,莫过于作为信号的条件刺激，出现在需要你做准备的，非条件刺激之前。
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So, in terms of what it is that you need to prepare and bring with you for the exam, you need to bring your MIT ID, especially if you haven't been showing up regularly to your recitations and you aren't 100% sure if your TA knows exactly who you are, you need to make sure you have your MIT ID with you.
那么，关于你需要做哪些准备,考试可以带哪些东西，你需要带着你的学生证，尤其是如果你没有经常地参加,习题课,你不能百分之百保证,你的助教确实认识你，那么你更得确保自己到时带着学生证。
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So that's just a little bit of a check for yourself, and it should make sense because what you're doing is you're calculating the difference between energy levels, so you just need to flip around which you put first to end up with a positive number here, and that's a little bit of a check that you can do what yourself.
所以你们总要确保括号，离得这项是正的，这是你们自己,可以做的检查，这事很有道理的，因为你们做的是计算能量差,所以你需要调整顺序来保证一个正数，这是你们自己可以做的检查。
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All you have to do is mutate the DNA, which is very straightforward to do in molecular biology, and now you can tag absolutely any protein that you're interested in.
你所需要做的就是使DNA变异，这在分子生物学力是很容易做到的，你可以用它标记,任何你感兴趣的蛋白质。
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