Preliminaries

Def: A matrix $A \in M_n$ is normal if $AA^∗ = A^∗A$, that is, if $A$ commutes with its conjugate transpose.

Def: A complex matrix $A$ is unitary if $AA^∗ = I$ or $A^∗A = I$, and a real matrix $B$ is orthogonal if $BB^T = I$ or $B^TB = I$.

There is no so-called “orthonormal” matrix. There is just an orthogonal matrix whose rows or columns are orthonormal vectors.

Needs polish!

前略。

Beamer 引用参考文献与文章类似，只是一开始听说 beamer 不支持 \cite，搞得我走了不少弯路（其实是可以的）。

Story

The Exponential distribution is the continuous counterpart to the Geometric distribution. The story of the Exponential distribution is analogous, but we are now waiting for a success in continuous time, where successes arrive at a rate of $\lambda$ successes per unit of time. The average number of successes in a time interval of length $t$ is $\lambda t$, though the actual number of successes varies randomly. An Exponential random variable represents the waiting time until the first arrival of a success.

高斯分布的微分熵

$X \sim \mathcal{N}(\mu, \sigma^2)~$，$\displaystyle f(x)=\frac{1}{\sqrt{2\pi\sigma^2}}e^{-\frac{(x-\mu)^2}{2\sigma^2}}$，其微分熵推导过程如下：

This article needs polish, do not truely trust it!

Vim is so-called the god of editors, but not so friendly to new users. Today we will cover some techniques and trick of vim, for further reference.

General Pattern

A vim operation consists of three parts, namely

[OPERATOR][NUMBER][MOTION]

where

• OPERATOR - what you want to do? This mainly covers copy, cut, paste, etc.
• NUMBER - how many times do you want? It’s nothing but repeating the operation NUMBER times, and it’s optional.
• MOTION - where do you want to go? This point out the scope where the OPERATOR applies.

Note: order does not matter sometimes.

更改字体

Melody 主题字体配置文件在 $BLOG/themes/melody/source/css/var.styl，其中 $BLOG 为 Hexo 博客根目录。截取一段如下：

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// Global Variables
$font-size = 16px
$font-color = #1F2D3D
$rem = 20px
$font-family = Martel Sans, Spectral, Lato, Helvetica Neue For Number, -apple-system, BlinkMacSystemFont, Segoe UI, Roboto, PingFang SC, Hiragino Sans GB, Microsoft YaHei, Helvetica Neue, Helvetica, Arial, sans-serif
$code-font = Monaco, consolas, Menlo, "PingFang SC", "Microsoft YaHei", monospace, Helvetica Neue For Number
$text-line-height = 2

这样的话就可以使用自定义的字体 Martel Sans 了。但是这仅限于在本地使用，因为别人的计算机中可能没有这个字体。所以必须制定网页去哪儿加载这个字体。一个方法是，将你系统的字体文件复制到博客根目录的 source/fonts 文件夹。

Markdown 是一门轻量标记型语言，因其简单易用而受众甚广。但是正因其简单，故而也有一部分局限性（虽然说它保留的即是最常用、最基本的排版功能）。本文就来说说在使用 Markdown 排版的时候，如何引入一点 HTML 的技巧来帮助我们排版的更加好看。

对于 Linux 用户，在 $HOME 文件夹下，一般都有大量的隐藏文件，形如.conf,.xxxrc等，这些都是程序的配置文件。很多人也许花了一个下午，一天，甚至一个星期，折腾某某程序的配置文件。如果这些轻易丢失了，那就是浪费生命了！所以，如何将这些文件备份，成了很多人必须要问的一个问题。

1. 事前准备

先想好为什么要刷机？想清楚了吗？真的想清楚了吗！好的，接下来我们要做的事应该是打开一堆网页，一堆对应自己机型的刷机教程帖，还要做好重要数据备份，确保“不成功，也不能成仁”。好的，那就开始吧：