是笔记，不是文章。其中一些是完整的论证；大部分只是我不想再重推一遍的推导，或者我搞错了、后来不得不改掉的东西。
Notes rather than articles. Some of these are complete arguments; most are a derivation I wanted to stop redoing, or something I got wrong and had to fix.
第三周就会学到的那个分解，以及其中没人提的一点：三项里有一项不归你管。
The decomposition everyone learns in week three, and the part of it that nobody mentions: one of the three terms is not yours to control.
一行凸性，三个有用的不等式。写在这里，好让我不用每次做优化论证时都从头搭一遍。
One line of convexity, three useful inequalities. Written down here so I stop rebuilding it from scratch at the start of every optimisation argument.
一本讲测量误差的书的笔记，以及其中一个改变了我做实验方式的观点。
Notes from a book about measurement error, and the one idea from it that changed how I set up experiments.
论文里的图大多比它们需要的更难看，而修法通常是删而不是加。这是我用的样式表。
Most figures in scientific papers are worse than they need to be, and the fix is usually deletion rather than decoration. Here is the style sheet I use.