Archive for the 'Academic | 学海无涯' Category

四十八分之四十七:致谢

Thursday, October 11th, 2012

都说前言和致谢是最可以自由发挥的地方,所以用它来凑数吧

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Today is the mid-autumn day in China. It is the day when the moon is experiencing the eighth full phase in the Chinese lunar calendar. It is a traditional Chinese festival in which relatives and close friends reunite. The reunion is, on the one hand, to celebrate the harvest in the autumn as the Oktoberfest in Kitchener-Waterloo, and on the other hand, to provide an opportunity to gather relatives and close friends together as the Thanksgiving in western Countries. The tradition snack prepared for this particular day is the mooncake. A typical mooncake is a round pastry which resembles the moon and has the implication of reunion, perfection, and happiness. This festival has been listed as an “intangible culture heritage” in China and made as a public holiday. In the past 28 years, I have spent more than four years in three cities and celebrated this festival. These past experiences, I think, are the nodes which can artfully connect my mundane life and my academic life.

I was born in Chengdu which is famous for its temperament of leisure and comfort. I spent 18 years in Chengdu before college and have strong sense of affiliation and nostalgia for this city. Now most of my classmates from middle schools have started to work across China. So that means, at the same time I am writing the acknowledgement, some of them are on the way back to the hometown. During the last 10 years I spent outside Chengdu, they told me the development in Chengdu from time to time. The leisure city in my memory has changed tremendously in the last decade. Road tunnels, large shopping malls, and high-tech zones sprouted out and the city expanded ceaselessly. While the real sprit of the city, life enjoyment with playing Mahjong under the shade of trees, eating dedicate Szechuan cuisine in the midnights, and drinking jasmine tea in public parks faded away over time.

I spent 6 years in Beijing for the undergraduate and master degree’s study. Beijing is, by all means, a complex city. In my opinion, it tries very hard to work as the center of commerce, culture, and politics simultaneously. It also bears too much burden of history and development at the same time. In Beijing, we can find a distinctive residential system, Hutong, in which ordinary people live in a crowded and humble accommodation but with higher level of interactions among neighbors. Staying under the same roof is rather an emotional expression and means more mutual support rather than tolerating the disadvantages. In the meantime, skyscrapers and post-modern buildings grew constantly, like the Olympic stadium (the Bird Nest and the Water Cube), and the central television building. Visiting the CBD in Beijing in rush time would be a disaster for a “foreigner” in this city, regardless of any transport methods you choose. You will experience either “people mountain people sea” if you choose the subway, or terrible traffic jam if you choose taxi, or detrimental air and noise even if you choose walk or bicycle. It seems there are always dilemmas about the land-use issues in Beijing. During major festivals and public holidays, Beijing is facing the extensive challenges of accommodation, transportation and safety to cater all the tourists and nostalgic migrants.

In the last four years, I was living and studying in Waterloo, a pretty “small” city in Canada (However, Waterloo region was ranked as number two on the performance of economy among Canadian urban centers). Even if it is a relative small city, diversity sprawls out the whole city. It has a large amount of international students here since it has two well-known universities. It works as a new hub for the high-tech development in Canada surrounding the flagship blackberry company, RIM. It also has a heritage of German immigrants. The district along the University Avenue between University of Waterloo and Wilfrid Laurier University was described as a “student ghetto” with occasional vandalism and accidents in two years ago. And recently several high rise condominiums in the same district are in the final stage of construction and ready to welcome the increasing amount of students here. Homeowners used to work in RIM are moving out the city due to the layoff and a restrictive requirement of a rental housing license. During the festival, my Chinese fellow students are gathering together, eating mooncakes bought from local Chinese grocery stores in Waterloo or Toronto, tele-communicating with friends and relatives in the other half of the Earth planet, and enjoying festival shows online.

It seems the land use continuously change in all the three cities, whether it is large or small. Also it looks like people can embrace the traditional customs and modern technologies at the same time. When new conflicts emerge and hamper our development, we – human beings – are adept at adjusting and improving. This is also true in academic development. A Ph.D study is a path toward improving the academic knowledge in a specific narrow way with innovative methods and results. It is not a leisure path, and therefore I want to express my sincere appreciation to all the people helping me during this path.

First and foremost, I want to express my gratitude to my Ph.D. supervisor, Dr. Dawn Parker. In the past three years, her enthusiasm, knowledge and encouragement always inspire me to hurdle the obstacles in completing all the research. She gave a first impression of strictness in my comprehensive exam. But after she became my supervisor and I took her elaborately prepared course, I start to find that she really care about students. And ainsightfuls discussion with her becomes weekly intellectual challenge and enjoyment, which guide the path for me to be an independent researcher with integrity.

I would also like to thank my former supervisor, Dr. Jonathan Li, for helping me getting through the first year, the toughest year, in Canada. With his consistent support and help, I gradually adapted to the life in Canada and successfully passed the comprehensive exam. In addition, I am indebted to many colleagues for their generously help. I am especially grateful to Shipeng Sun, Tatiana Filatova, and Derek Robinson. Because of your kind assistances in reviewing and commenting on my work, I am able to finish the Ph.D study with fruitful outputs. All of you are great persons who are not reluctant to share your experiences in not only academic sphere but also social activities. I really enjoy spending time with all of you, and love your sense of humor. I am hoping we can continue our collaboration in the future.

I wish to thank many colleagues in University of Waterloo, University of Michigan and Beijing Normal University, who provides a simulating environment to learn and to growth. They are Dr. Peter Deadman, Raymond Cabrera, Tianyi Yang, and Calvin Pritchard from UW, Dr. Dan Brown from UM, Dr. Peijun Shi and Dr. Chunyang He from BNU. In particular, I want to thank the secretaries in the department of environment and school of planning, Lynn Finch, Susie Castela, Lori McConnell, Edie Cardwell, for your assistances in various ways. I also want to thank the funding provided by the department, the graduate office in UW, and the China Scholarship Council for helping me pursuing a Ph.D degree as an international student.

Friends play a really important role in accompanying me accomplishing the fifty-month living in Canada regardless of where you are living. It would be a really tough journey to study abroad without the funny and happy time spending with all of you. Among all the friends, Miao Jiang, Yuanming Shu, Yue Dou, Suo Huang, Zhenzhong Si, Quan Long, Jianqing Wang, Xi Yang, George Xie, Yi Yin, Yiqiao Zhou, Zhen Li, Yuanyuan Zhao, Yang Yang, Zhifeng Liu and Tiechun Wang deserve special mention.

Lastly, and most importantly, I wish to thank my parents, Zeyuan Huang and Biying Xie. They bore me, raised me, supported me, taught me, and loved me. To them I dedicate this thesis.

四十八分之四十五:学一点社会学,当然也有数学和物理学

Tuesday, August 14th, 2012

Canada day 2012

前一个月说的是囚徒困境(prison‘s dilemma),其实在社会学和地理学交界的这个区域还有很多很有趣的研究

第一个就是Schelling’s segregation model(谢林的隔离模型),最早这个模型是来解释居住模式的,特别是北美的白人和黑人的隔离居住的现象。谢林用了一个很简单的模型,在一个棋盘状的空间(围棋),每一个格子就像一个细胞,里面可以住一个人。黑白各代表黑人和白人。首先让黑白等量的棋子随机分布在棋盘上,留下20%-30%的空间为空白。之后每一轮随机选择一个棋子,看他在自己的邻里空间居住是否满意,而衡量满意的条件就是在周围8个邻居中是否有有足够的同种颜色的棋子(一般是3-4个同种颜色为阈值)。如果满足条件就不移动,如果不满足就在空白的区域找可移动也可以满足阈值需求的格子。

这个模型随后被各个研究者各种修改,但重要的是只是这么一个简单的条件就让看似杂乱无章的随机分布呈现出团块状的隔离形态。更重要的是,这个社会学模型更好的验证了《Social Atom》这本书里面的一个论点:“社会学其实也是一种物理学,社会学的理论其实跟物理学理论有巨大的可类比性。”在2006年的时候,确实有物理和数学基础很好的研究者把这个模型用数学方法类比成了物理学的聚集现象(Vinković, D., Kirman, A., 2006. A physical analogue of the Schelling model. Proceedings of the National Academy of Sciences 103, 19261-19265)

其实,这个模型在网络世界也可以应用,物理的空间被信息空间和人的关联度所联系,就变成网络空间的隔离状态。这可以很好的解释各大门户网站同质产品但是用户互相隔离的状态。

另一套社会学研究是出自《Tipping Point》这本书,其实它讲的也是一个社会学地理学常见的模型,传染模型,但是书用了更好的社会案例来阐述这个模型。在传染模型中,有几个必要条件,要有集点,也就是书中所提到的maven、connector等特殊个性的人,他们负责发现新潮流,翻译新潮流,引领新潮流;第二个条件是沉迷性,玩游戏是最有说明性的。最后就是要有一定便于传染的环境,比如说是靠接触传染的传染病就需要有类似北京地铁这种比较容易密集接触的环境,而时装潮流的传染最好就要有比较容易发布这种潮流的契机(比如798文化区或者时装周等)。

无论是上一个隔离模型,还是这个传染模型,其实都回归到了所谓的Tobler‘s地理学第一定律这一点,也就是(空间上)隔的越近的事物属性更相似,当然这个距离可以扩大的人际交往或者网络空间这种非实体的距离。从另一个方面看,也一再提醒我们,要做一个独立思考,特立独行的人是何其的难

第三个经典问题是位序规模问题,这个也在《social atom》里面有所提到,这也是一个非常著名的普适的现象。这个现象简单来说就是一个事物的规模和它的排序呈现一种幂指数分布规律(power law)。比如城市的大小,如果将一个国家的城市从大到小排序,横坐标它的排序,纵坐标是它的城市大小,最后会排列出类似幂指数分布的一条曲线。而这种规律无论你是换一个国家(不随空间改变),换一个尺度(变成全球,或者一个省,不随尺度改变),换一个时间(不随时间改变),都能较好的满足。而现实生活中,这种位序规模出现在很多的社会、自然现象中。比如河流的分叉、公司的大小、能量的传递等级。

而迄今没有一个理论能完美的解释这种现象。而这种现象在很大程度上类似物理现象,就像万有引力的理论,它也不随空间,尺度和时间改变。当然,也有人用物理学和数学尝试了解释,并且推导了和分形之间密不可分的关系。

所以,我总觉得,学地理的,总应该读一点现在的社会学研究。这一种用物理学或者数学来解释社会现象的思潮,让人觉得很有趣。以前人们都说社会学研究的是一个个独特个性的人,不可能找到一个理论,但是物理学里面电子的空间位置不也是一个个随机和独特的过程吗?但是无论是社会还是原子,总保持了在聚合之后涌现(emergent)出来的稳定属性。

四十八分之四十四:prisoner’s dilemma

Saturday, July 14th, 2012

postcard from Waterloo Station, London, June 2012

读大名鼎鼎的《the selfish gene》的时候,没想到里面也用了一个章节来讲囚徒困境(prisoner’s dilemma)问题。这个问题也是我在接触了智能体模型(Agent-based model)后在相关文献中最常出现的引用之一。其实这也是社会学或者说博弈论的一个经典案例,案例简单来说就是你和你的共犯被抓,警察将你们分开审讯,作为疑犯你和你的共犯可以采取两种措施,一种是死不承认,一个是坦白从宽。由于每个人都有两个选择,排列组合之后就有了四种结果。都不承认的是两人都受到轻微惩罚,而互相揭穿的结果是两者都接受中等程度惩罚,而一方背叛而另一方不供认的结果是被背叛的收到最重的惩罚而背叛者不受到惩罚(以下是wiki上面的来源)。

The prisoner’s dilemma is a canonical example of a game analyzed in game theory that shows why two individuals might not cooperate, even if it appears that it is in their best interest to do so. It was originally framed by Merrill Flood and Melvin Dresher working at RAND in 1950. Albert W. Tucker formalized the game with prison sentence payoffs and gave it the “prisoner’s dilemma” name (Poundstone, 1992). A classic example of the prisoner’s dilemma (PD) is presented as follows:

Two men are arrested, but the police do not possess enough information for a conviction. Following the separation of the two men, the police offer both a similar deal—if one testifies against his partner (defects/betrays), and the other remains silent (cooperates/assists), the betrayer goes free and the one that remains silent receives the full one-year sentence. If both remain silent, both are sentenced to only one month in jail for a minor charge. If each ‘rats out’ the other, each receives a three-month sentence. Each prisoner must choose either to betray or remain silent; the decision of each is kept quiet. What should they do?

而这个问题的核心是研究对象(在这个情况下是疑犯)应该采取什么措施。而在书中,得出了一个有趣的结论——nice guys finish first,也就是说遇到这种情况,友善的策略(strategy)的结果是最好。在这个实验中,设计者请了很多人来设计不同的策略,不断重复这个实验,看最后谁的结果最好(惩罚最轻,或者收益最大),夺冠的策略是Tit for tat(an English saying meaning “equivalent retaliation”)。这个策略就是全面模仿对方的策略,只要对方沉默,我也沉默,只要对方背叛,我下一轮也背叛。换成中文有点跟屁虫的味道,同时又有点大好人的感觉,再加一点睚眦必报(很奇怪这种策略要翻译成中文都是比较负面的词汇)。而相对而言,比较邪恶的拥有主动背叛的策略都得不到善果。

而我遇到的智能体模型,大多是用它来处理资源的分配问题,因为主权不明确的公共资源,由于它的外部性(externality)作用(比如空气),不同的决策者会对它不同的对待方式。比如环保主义者,住户,政府,投资者和产业者。在这个情况下不再是善有善终的结果了。我觉得很大的问题是,不同于前面提到的策略,另一种决策过程(decision making process)在现实生活中起作用。利益相关者(stakeholder)不再单一采取一种静态的策略,而是在学习和适应(learning and adaptation)的过程中不过改变自己的策略,每一个决策是根据自己以前策略的结果和广义上“邻居”的策略信息综合得出的,所以结果更莫测一点。

这一切看起来很学术,但是换一个话题一下就很容易明白,那就是恋爱。爱情中的人总会遇到这种进退维谷的时候,有些时候你会选择原谅,有些时候你会选择报复。总体来看,长长久久的爱情大抵都是互相懂得原谅的,而主动报复对方的一半时最迅速结束自己的姻缘的。但是大多数人不是一见钟情,一生一世,而是在不断遇到新人的过程,你自己的恋爱策略也慢慢变化着,最后能不能达到平衡状态也要看天时地利人和。所以博弈论下面的爱情关系教会至少两件事情,一者是要大度,二者是要学会成长,豆瓣上面那些恋爱的故事就是一个个实证案例(empirical cases)。

P.S. 书里面提出了文化基因meme,但是不知道为什么现在人们对这个词的发音都是类似“密密”,明明文章里面提到其实这个词的发音应该是模仿基因(gene)的单音节(monosyllable),而应该跟Cream押韵(It should be pronounced to rhyme with ‘cream'”),不知道为什么这种发音发生了变化。

四十八分之四十一:complexity

Tuesday, April 17th, 2012

Ottawa

张学友有首歌叫《秋意浓》,讲的是秋天愈发凄切的故事,但是没有一首歌叫春意浓,可能是由于春天太复杂的原因。春意真是乖张任性,三月的时候已经艳阳高照,过不了几天又鹅毛大雪。刚看见松鼠候鸟出来迎接春光明媚,哪知道接下来就是几天的细雨绵绵。想说吹面不寒杨柳风,结果一出门天气三变加加减减不断换衣服。这就好像她要强调自己有摸不透的复杂性。

科学理论也是越来越复杂。最早理论也就归纳和演绎的二分法。比如地价,越靠近城中心越贵,而城中心大多是商务区,再往外是轻工业区、住宅区、重工业区、一直到农田,大多城市脱不开这种套路,这是人们通过观察总结来的,叫归纳法。而有人想了一套理论来解释这种现象,这种分布和价格是由于供需和竞价决定的,中央地区由于拥有最好的通达性,自然最有吸引力,而商务区由于利润高,所以可以给出最高的竞价。郊区的农田分布也是这个道理,即分布和地价与通达性和利润有直接的关系。因此,人们用这个理论来解释不同城市的分布问题,有些地方由于特殊的地形和发展的规划政策限制,对这种分布衍生出一些些变体,但最基本的原理不变,这就是演绎。

问题是,现在的科学家总不满足于这种单纯的归纳演绎二分法,提出了直观法。如果要打个比方,这种方法与物理里面的量子态(薛定谔的猫)、不确定性、平行宇宙有很大的关系。简单来说,也就是城市分布是复杂的,现在的形态虽然有理论基础,但是这种理论推导的结果不一定是现实。换句话,也就是现实只是理论的结果之一(很像平行宇宙哈)。而人在这种复杂性中起了非常大的作用。

所以现在建模型都是靠复杂性的假说,其中三分理论演绎,三分经验归纳,三分主观直觉,还有一分就是随机天意。因此繁衍出很多新的词汇,乍一听很玄乎,其实概念很简单。比如路径依赖(path-dependence),这个很简单,用蔡康永的一句话解释最好:“15岁觉得游泳难,放弃游泳,到18岁遇到一个你喜欢的人约你去游泳,你只好说“我不会耶”。18岁觉得英文难,放弃英文,28岁出现一个很棒但要会英文的工作,你只好说“我不会耶”。人生前期越嫌麻烦,越懒得学,后来就越可能错过让你动心的人和事,错过新风景。 ”

另一个概念是非线性(nonlinearity),这个也很好解释,就是说哪怕你学了游泳,你也不一定能和喜欢的人终成眷属。哪怕学好了英文,也不一定能在英文工作在如鱼得水。因为爱情不是看谁游泳游得好,而英文工作也不是不看社交能力。

还有一个概念叫异质性(heterogeneity),这个更好解释,就是说虽然错过了这个约你去游泳的姑娘,说不定因此碰上了不爱游泳的另一个姑娘。虽然错过了英文工作,说不定在其他方面有更适合自己才能的工作。每个人都是独立的特异的个体,这也就是为什么我觉得真的平淡无奇的田馥甄五月天罗志祥也有一大堆粉丝

这一切和在一起就成了涌现性(emergent),虽然对于这种涌现性能不能用突然和惊奇(surprising)来形容还存在争议,但是它想表达的就是一加一大于二的效果。

至于常见的随机性(stochastic),不确定性(uncertainty)就更不需要解释了。最近看到一篇文章讲遍历性(ergodicity),看来又要迎来新的“性分析”了

皇家植物园之春花

Sunday, May 15th, 2011

royal botanical garden
蟹爪兰 仙人掌科

虽然大部分植物还没有开花,哪怕是那些先花后叶的,但是皇家植物园的温室里面也有一些花开了
再加上外面那些开得很早的花草,构成了这幅景色,当然,这要多谢Kevin的好友Jennie帮忙识别

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四十八分之二十三:topophilia

Tuesday, September 28th, 2010

029

过去一个月,最重要的两件事情之一就是签了个合同买了iphone4,现在沉迷于Solomon‘s Boneyard(简称SB)的游戏之中。很多人都问我感觉,虽然iphone4在国内马上要变成街机(报道上每2秒卖出1部),不过我觉得除了电池不经用之外其他都很好,所谓的信号问题我没碰到,用iphone+skype就可以移动着给家里打电话了,难怪实验室印度MM每次提到Skype都一副感恩戴德的样子(她老公在Seattle)

另一件事情,就是驾照路考过了,跟教练练车也有10来个小时了(每小时40刀学费),虽然一上车的时候还是很紧张,不过Jimmy是一位胖胖的可爱的女考官,在一个红绿灯碰到了葬礼车队(funeral session),本来看变灯要开出去,结果它们根本不遵守交规,Jimmy就叫我等等,其他都是有惊无险,考试成绩还挺高,马路杀手准备上路。

在整个上半年,我几乎看完了东野圭吾所有有翻译的作品,其中除了《嫌疑人X的献身》是在回国的飞机上看的电影,以及《新参者》是看的电视剧之外,其他都是书,多谢了电子书。整个书单包括(按照拼音排序):
《白夜行》,《绑架游戏》,《毕业前杀人游戏》,《变身》,《濒死之眼》,《超 杀人事件》,《沉睡的森林》,《单恋》,《毒笑小说》,《恶意》,《放学后》,《分身》,《过去我死去的家》,《幻夜》,《回廊亭杀人事件》,《黑笑小说》,《红手指》,《湖边凶杀案》,《伽利略的苦恼》,《流星之绊》,《美丽的凶器》,《名侦探的守则》,《名侦探的诅咒》,《彷徨之刃》,《圣女的救济》,《杀人之门》,《时生》,《十一字杀人》,《使命与心的极限》,《宿命》,《信》,《雪地杀机》,《预知梦》,《侦探伽利略》
加上影视一共36部(按照豆瓣的记录没有全,不过其他的几本找不到),如果豆瓣我读也可以按照电台那样调教的话,会一直给我推荐侦探小说吧。其中最好的作品,绝对是《白夜行》,读了之后,久久都走不出那个故事的调调,作为非典型的侦探小说,比杀人更值得回味的就是对于整个社会环境和现代生活的描写和烘托。

反观东野的作品,除了名侦探系列算典型的侦探系列(虽然里面的侦探也是物理学家),三笑小说算讽喻侦探小说界的作品外,其他作品大多都是走社会和内心交战这个路数,一者描写整个日本现代社会的人情世故,一者描绘故事主角的内心挣扎,而白夜行算其中在叙事角度,情节节奏和悬念设置最与以上的中心相扣的作品,强烈建议读了之后体味那一种“只希望能手牵手在太阳下散步”的感觉。

另外由于《1Q84》太受追捧,忍不住看了Book1和Book2,现在就是冰天雪地跪求Book3的时候,趁此顺手看了《挪威的森林》和《海边的卡夫卡》,前者在我看完的时候就被图书馆召回了,后者是看的电子版,对于村上春树的想象力和主题表达能力我只能五体佩服,对于面对墙和蛋选择站在蛋这一边的的村上,当年在写《海边的卡夫卡》的时候,会想到以后自己要在领奖的时候讲那么坚决的政治立场的发言吗?我身边有很多人,每天都抱怨自己生活的单调无趣辛苦繁琐,而《海边的卡夫卡》绝对是推荐给彷徨绝望低落的人的一本好书

最后,就是我又想翻译段义孚先生的自传了,虽然自己忙得跟鬼打墙一样,但是由于最近在看老先生的《Coming home to China》,看他讲起当年回国的那些事情那些人。特别是有蛮多人关注我blog的一个原因就是老先生的当年讲座的内容,所以,我又想纠集一堆人翻译他的作品。不过,对于沟通,协调,出版社,版权等等还是挺麻烦的。

关于学术方向,就是我自己做了一个ABM方向关于residential choice(其中涉及segregation,gentrification,urban sprawl,urban land use,planning等等)的总结对比,马上就要进行到实际的实验设计上了,可能会用到基于过程的全局敏感性分析。