I’m Zigang Xiao (Ivan),
a PhD candidate
in University of Illinois.

about me

I write about technical stuff in the field of computer science, my hobbies, including guitar playing and ballroom dancing, and my study abroad experience in US. And yes, some of my posts are in Chinese ;)



found on


- - posted in chinese, personal

Wisdom Teeth (source)
Wisdom Teeth (source)

在快奔三的年纪,终于长出了最后一颗智齿。本来想着说这辈子不用拔智齿的——因为我25岁前就已经长完了三颗智齿,并且都 align 得非常好,并没有阻生。之前在中国时的医生也告诉我,没有必要拔掉,因为他们出来得迟,因此比起其他牙齿也会掉得迟。所以以后牙齿掉完后,他们还会在那里,可以做到固定镶牙的用途。当然我在美国没有听到有医生这样提起的,而且美国的习惯是 4 颗一起全部拔掉,一了百了!听起来有点 scary,只是他们的考虑也不是没有道理:智齿一般会长歪,即使没有长歪,也可能引发各种疾病,比如由于长得比较靠里,比较难清洁到,因此很容易蛀牙。更甚的是,蛀牙后,会引起正常的牙齿也蛀牙!这个情况就发生了在我身上:我的下面两颗支持都有蛀牙,并且引起了旁边的蛀牙!为了这个问题,我已经补过两次牙齿。这成为了我这次拔掉他们的最大原因。

Popular Watches Under $150

- - posted in watches

I’ve been looking around entry-level watches for some time. Recently, I answered a question in Zhihu (Chinese Quora), and I feel like to transcribe this collection in my blog.


- - posted in thoughts


有感于最近香港要求普选的民运,心中大概有点想法。考虑到自己对政治的认识与时间的限制,为了防止与 别人无谓的争辩, 不想把这些想法发到社交网络上,毕竟,这只是个人的想法,或者更严格来说, 是一种理念。因为很多主义与思想,都没有绝对的对错,我们只能做到根据自己的人生观与思想来 做出取舍。而偏偏这个世界上又很多人喜欢跟别人 argue,一定要说服别人为止——我根本没有这个时间 与精力去辩论。另外,这也同时印证了我为什么是 pro-精英主义的,我深知自己对这些事物的认识 不够,所以自觉需要更严谨的学习才有资本与别人争论。我相信多年以后,自己的看法一定又会 有所改变。彼时回首看这些文章,一定会觉得自己幼稚。不过无论怎么说,还是记录下自己的想法。

Notes on Maximum Likelihood, Maximum a Posteriori and Naive Bayes

- - posted in machine learning, probability

Let \(\data\) be a set of data generated from some distribution parameterized by \(\theta\). We want to estimate the unknown parameter \(\theta\). What we can do?

Essentially, we want to find a most likely value of \(\theta\) given \(\data\), that is \(\arg \max P(\theta | \data)\). According to Bayes Rule, we have

\[ P(\theta \given \data) = \frac{P(\data \given \theta)P(\theta)}{P(\data)} \]

and the terms have the following meanings:

  • \(P(\theta \given \data)\): Posterior
  • \(P(\data \given \theta)\): Likelihood
  • \(P(\theta)\): Prior
  • \(P(\data)\): Evidence

Fix Mid 2009 MBP RAM Not Recognized Issue

- - posted in DIY, Mac

Possible cause of unrecoganized RAM
Possible cause of unrecoganized RAM

A few days ago, I encountered an issue which seems to be common among mid-2009 MBPs: one of the RAM (in slot 1) is not recognized anymore. Or, sometimes it is recognized, but after sleep and wake up, the computer freezes and impossible to recover but force power off.

Replacing SATA Cable in Mid 2009 MBP

- - posted in DIY, Mac

Replacing MBP cable
Replacing MBP cable

Recently, my mid 2009 MBP (Model A1278) fails to recognize the hard drive. My first bet was another disk failure on me, but it was not the case. I took down the hard drive and put it to a mobile hard drive case and it can be read smoothly.

My Octopress Blogging Flow

- - posted in blogging, octopress

Writing in Sublime Text and previewing in Marked
Writing in Sublime Text and previewing in Marked

After blogging with Octopress for a while, I have already gained some insights on it, and my publishing flow has been smoother. I think it is right time to share my flow as a reference.