一 : 今天,奋斗的起点
昨天带着回忆默默的逝去,今天携着希望悄悄来临,而明天,又闪烁着光辉等待着人们。有沉浸在回忆中,他们依恋明天;有的人只迷醉在梦幻中,他们企盼着明天。这两种人,都忘了最应该珍惜的今天。今天不就是短短的一天吗?我从明天开始勤奋学习,有些人是这样的想,也是这样的做。朋友,不觉不怀疑你的真诚,但为什么要把事情放到明天呢?日月匆匆,到了明天,明天又变成了今天,而每个今天之后都有无穷无尽的明天。那么,你的决心,你的力量理想,哪一天才能变成行动呢?变为现实呢?
莎士比亚说:“抛弃时间的人,时间也回抛弃他。”我说:“抛弃今天的人,今天也会抛弃他,而被今天抛弃的人,他也就没有了明天。”
“明日复明日,明日何其多,我生待明日,万事成蹉跎。”短短的几句诗,是先辈千折百曲历经磨难的生活体验的结晶啊!古人有感于此,于是有了“悬梁刺股”、“囊虫映雪”、“凿壁偷光”的勤学佳话。现在我们条件优越了,不是更应该珍惜,抓紧今天的分分秒秒吗?
抓住了今天,就是抓住了掌握获取知识的机会;抓住了今天,就是抓住发明创造的可能。聪明、勤奋、有志的人,他们深深懂得时间就是生命,甚至比生命还宝贵,他们决不会把今天宝贵时光虚掷给明天。
相反,对有些人来说,时间就像代表它的那本日历,撕了这张,还有下一张,撕完了这一本,还有下一本,却不知道在洁白如雪的日历上留下自己辛勤奋斗的汗水和学习、工作的收获。那样,他们从呱呱落地到长眠地下,都是在闲散和观望,等待之中度过的,如果人的一生如此度过,那么消逝的岁月将如一场凄凉的悲剧,留在个人生命史上的回忆,将拌和着悔恨、痛惜和哀伤的泪水……
朋友,不要沉湎昨天,不要观望明天,一切从现在开始,从今天开始吧!
今天,是奋斗的起点!
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二 : 我奋斗了18年不是为了和你一起喝咖啡PK我奋斗了18年才和你坐在一起喝咖
编者语:大概5年前,编者在网上看到“我奋斗了18年才和你坐在一起喝咖啡”的贴子时,不甚唏嘘;5后,又偶尔看到“我奋斗了18年不是为了和你一起喝咖啡”一文,又顿生感慨之情。而网友都市隐士评论“其实我们都应该感恩,因为不论贫贱,我们都来到了这个世界,都在品味这个世界的生活,我们都生存着,并会平等的迈入坟墓”之精彩深隧,以及网友赌侠说“我们出生的时候,上帝已发好了牌,抓的牌好与不好,我们已无法抗拒,我们唯一能做的,就是把手中的牌出好,哪怕是一把烂牌”之积极进取,让编者不禁有“奇文共欣赏”之念,遂编辑成文,以飨读者。我奋斗了18年才和你坐在一起喝咖啡□文|麦子我的白领、金领、黑领朋友们,如果我是一个初中没毕业就来沪打工的民工,你会和我坐在“星巴克”一起喝咖啡吗?不会,肯定不会。比较我们的成长历程,你会发现,为了一些在你看来唾手可得的东西,我却需要付出18年的努力。从我出生的一刻起,我的身份就与你有了天壤之别,因为我只能报农村户口,而你是城市户口。如果我长大以后一直保持农村户口,那么我就无法在城市中找到一份正式工作,无法享受养老保险、医疗保险。你可能会问我:“为什么非要到城市来?农村不很好吗?空气新鲜,又不像城市这么拥挤。”可是农村没有好的医疗条件,那年SARS好像让大家一夜之间发现农村的医疗保健体系竟然如此落后,物质供应也不丰富,因为农民挣的钱少,贵一点儿的东西就买不起,所以商贩也不会进太多货。春节联欢晚会的小品中买得起等离子彩电的农民毕竟是个别现象,绝大多数农民还在为基本的生存而奋斗,于是我要进城,要通过自己的奋斗获得你生下来就拥有的大城市户口以及户口带来的相关待遇。考上大学是我跳出农门的唯一机会。我要刻苦学习,小学升初中,初中升高中,高中考大学,我在独木桥上奋勇搏杀,眼看着周围的同学一批批落马,前面的道路越来越窄,我这个佼佼者心里不知是喜是忧。激烈的竞争让我不敢疏忽,除了学习功课,我无暇顾及业余爱好,学校也没有这些发展个人特长的课程。进入高中的第一天,校长就告诉我们这三年只有一个目标——高考。于是我披星戴月,早上5:30起床,晚上11:00睡觉,就连中秋节的晚上,我还在昏暗的路灯下背政治题。而你的升学压力要小得多,竞争不是那么激烈,功课也不是很沉重,你可以有充足的时间去发展个人爱好,去读课外读物,去球场挥汗如雨,去野外享受蓝天白云。如果你不想那么辛苦去参加高考,只要成绩不是太差,你可以在高三时有机会获得保送名额,哪怕成绩忒差,也会被“扫”进一所本地三流大学,而那所三流大学我可能也要考到很高的分数才能进去,因为按地区分配的名额中留给上海本地的名额太多了。我们的考卷一样我们的分数线却不一样,但是当我们都获得录取通知书的时候,所交的学费是一样的。每人每年6000元,四年下来光学费就要2.4万元,再加上住宿费每人每年1500元,还有书本教材费每年1000元、生活费每年4000元(只吃学校食堂),四年总共5万元。2003年上海某大学以“新建的松江校区环境优良”为由,将学费提高到每人每年1万元,这就意味着仅学费一项四年就要4万元,再加上其他费用,总共6.6万元。6.6万元对于一个上海城市家庭来说也许算不上沉重的负担,可是对于一个农村的家庭,这简直是一辈子的积蓄。我的家乡在东部沿海开放省份,是一个农业大省,相比西部内陆省份应该说经济水平还算比较好,但一年辛苦劳作也剩不了几个钱。以供养两个孩子的四口之家为例,除去各种日常必需开支,一个家庭每年最多积蓄3000元,那么6.6万元上大学的费用意味着22年的积蓄!前提是任何一个家庭成员都不能生大病,而且另一个孩子无论学习成绩多么优秀,都必须剥夺他上大学的权利,因为家里只能提供这么多钱。我属于比较幸运的,东拼西凑加上助学贷款终于交齐了第一年的学费,看着那些握着录取通知书愁苦不堪全家几近绝望的同学,我的心中真的不是滋味。教育产业化时代的我终于可以如愿以偿地在大学校园里汲取知识的养分!努力学习获得奖学金,假期打工挣点生活费,我实在不忍心多拿父母一分钱,那每一分钱都是一滴汗珠掉在地上摔成八瓣挣来的血汗钱啊!来到上海这个大都市,我发现与我的同学相比我真是土得掉渣。我不会作画,不会演奏乐器,不认识港台明星,没看过武侠小说,不认得MP3,不知道什么是walkman,为了弄明白营销管理课上讲的“仓储式超市”的概念,我在“麦德隆”好奇地看了一天,我从来没见过如此丰富的商品。我没摸过计算机,为此我花了半年时间泡在学校机房里学习你在中学里就学会的基础知识和操作技能。我的英语是聋子英语、哑巴英语,我的发音中国人和外国人都听不懂,这也不能怪我,我们家乡没有外教,老师自己都读不准,怎么可能教会学生如何正确发音?基础没打好,我只能再花一年时间矫正我的发音。我真的很羡慕大城市的同学多才多艺,知识面那么广,而我只会读书,我的学生时代只有学习、考试、升学,因为只有考上大学,我才能来到你们中间,才能与你们一起学习,所有的一切都必须服从这个目标。我可以忍受城市同学的嘲笑,可以几个星期不吃一份荤菜,可以周六周日全天泡在图书馆和自习室,可以在周末自习回来的路上羡慕地看着校园舞厅里的成双成对,可以在寂寞无聊的深夜在操场上一圈圈地奔跑。我想有一天我毕业的时候,我能在这个大都市挣一份工资的时候,我会和你这个生长在都市里的同龄人一样——做一个上海公(www.61k.com)民,而我的父母也会为我骄傲,因为他们的孩子在大上海工作!终于毕业了,在上海工作难找,回到家乡更没有什么就业机会。能幸运地在上海找到工作的应届本科生只有每月2000元左右的工资水平,也许你认为这点钱应该够你零花的了,可是对我来说,我还要租房,还要交水电煤电话费还要还助学贷款,还想给家里寄点钱让弟妹继续读书,剩下的钱只够我每顿吃盖浇饭,我还是不能与你坐在“星巴克”一起喝咖啡!如今的我在上海读完了硕士,现在有一份年薪七八万的工作。我奋斗了18年,现在终于可以与你坐在一起喝咖啡。我已经融入到这个国际化大都市中了,与周围的白领、金领朋友没有什么差别。可是我无法忘记奋斗历程中那些艰苦的岁月,无法忘记那些曾经的同学和他们永远无法实现的夙愿。于是我以第一人称的方式写下了上面的文字,这些是典型的中小县城和农村平民子弟奋斗历程的写照。每每看到正在同命运抗争的学子,我的心里总是会有一种说不出的辛酸与欣慰之情。写这篇文章不是为了怨天尤人,这个世界上公平是相对的,这并不可怕,但是对不公平视而不见是非常可怕的。我在上海读硕士的时候,曾经讨论过一个维达纸业的营销案例,我的一位当时曾有三年工作经验,现任一家中外合资公司人事行政经理的同学,提出一个方案:应该让维达纸业开发高档面巾纸产品推向9亿农民市场。我惊讶于她提出这个方案的勇气,当时我问她是否知道农民兄弟吃过饭后如何处理面部油腻时,她疑惑地看着我,我用手背在两侧嘴角抹了两下,对如此不雅的动作她投以鄙夷神色。在一次宏观经济学课上,我的另一同学大肆批判下岗工人和辍学务工务农的少年:“80%是由于他们自己不努力,年轻的时候不学会一门专长,所以现在下岗活该!那些学生可以一边读书一边打工嘛,据说有很多学生一个暑假就能赚几千元,学费还用愁吗?”我的这位同学忒不了解贫困地区农村了。我是70年代中期出生的人,我的同龄人正在逐渐成为社会的中流砥柱,我们的行为将影响社会和经济的发展。把这篇文章送给那些在优越环境中成长起来的年轻人和很久以前曾经吃过苦现在已经淡忘的人,关注社会下层,为了这个世界更公平些,我们应该做些力所能及的事情,让“老吾老以及人之老,幼吾幼以及人之幼”的人文情怀驻留我们的头脑。我花了18年时间才能和你坐在一起喝咖啡。三 : 蓝莲花咖啡~我和小伙伴们在一起
空虚寂寞的时候你会干什么?我一个好朋友现在每天晚上都在粘钻画,长达一米九的钻画啊,一颗钻一颗钻粘下去,眼睛要累瞎了。而且这东西也没个技术含量,反正无聊时我是不会做这个,喝咖啡去多好啊,多小资多休闲啊,哈哈。我住的地方离工大超近,作为黑龙江省内排名第一的大学,留学生是相当多的,学校周围咖啡简餐也是相当多的,一天换个地方,一个月你都不带重复的。咖啡简餐不好做啊,反正我眼见着旧的咖啡馆倒下去,新的咖啡馆如雨后春笋般的冒出来,能坚持下来的真没几家。我今天去的蓝莲花算是桥东街的老店了,11年开业,坚持到现在不能说不是奇迹啊。今天借着哈馆的光我们去涨知识去了。
蓝莲花咖啡馆,桥东街53号,很朴素的门面。蓝莲花是许巍很著名的一首歌,我一直很喜欢,曾经放在我博客首页好一阵子,蓝莲花代表着在路上,也代表着追求梦想。
我去的时候小伙伴们已经到了,真是小伙伴,每个人都要比我小十岁以上,你们说我心有多大,这么大岁数了还跟小朋友一起吃吃喝喝呢,方方球啊,你长点心吧。
美女老板先给我们普及了一下咖啡知识,防止我们错把珍珠当鱼目。就我这一生不羁放纵爱自由的性格,当时真是强挺着正襟而坐,其实我这个人挨上沙发就想出溜下去,淑女不是我的风格啊。
我能说我根本没好好听老板讲什么了,只关注她的玉手了吗。回到家里我还长久地看了这张照片,老肖说我明白你的意思---镯子。多年夫妻成亲人,老肖你真懂我,不过你不用卖血攒钱给我买镯子了,我的胳膊短,手指头也粗,配不上这么美貌的镯子。
她家的菜单呀杯子呀很多都是蓝色的,大概是为了配合蓝莲花的这个蓝字。我大概看了一下价格,都在20左右,比较亲民。
沙发也是蓝色的,看来店主装修的时候还是下了一番功夫的。
这个店在整个桥东街的咖啡馆里算是大的,下午的阳光也很好。而且还有包间,因为里面有客人就没拍上。
店里的吊灯都不错。
我比较偏爱这个,尤其在阳光下晶莹剔透的样子。亲们,店里有wifi的呀。
阳光很好,心情很好
谁不想拥有这样的小店,我真的很想。
从书架上我发现了一本很邪恶的书,我拍了一页让大家也跟着邪恶一下,哈哈。
也不知道那个糖需不需要付费,反正我偷吃了一块,韩国糖啊,自从看上了星星,我对韩国的一切都感兴趣了。
这是老板为了让我们学习分辨好咖啡特意上的基础咖啡。拿铁咖啡啊,卡布奇诺啊,都是在这个咖啡的基础上添加东西做出来的。因为没好好听课也不知道说得对不对,不对的地方请大家告诉我,随时改,方球虽然岁数大,但一点也没影响她谦虚,哈哈。
这个透明的杯子可以看出咖啡的品质很好,上面是油质。说到这里心都虚了,也不知道说的对不对,再次哈哈~咖啡杯的正确拿法,应是拇指和食指捏住杯把儿再将杯子端起,我经常满把握杯的喝法是不对的。
我的榛果拿铁咖啡,主要成分是牛奶还有基础咖啡。奶味很浓郁。店主说她家的奶都是进口的德国牛奶,成本很高的。
吃饭不拍照臣妾做不到啊,喝咖啡之前先用镜头消一下毒.你们想认识照片里的美女帅哥吗,如果她们同意我就把名字告诉你们,学历都很高啊,博士啊,硕士啊,我想正是这些好吃的给了他们上进的力量。
男士点的美式咖啡,我想问没有奶的咖啡好喝吗?
卡布奇诺,请问拉花能不能拉出个叫兽?原谅我吧,弱智少年问题多啊!
热巧克力可可,据说很甜很香。对了喝咖啡的时候转动杯子,吹气,发出声响,用小勺喝,给别人加糖这些行为都是违反礼仪的,我也是现学现卖哈哈。
巧克力摩卡
苏小苏同学不敢喝咖啡怕晚上失眠,店主贴心的给她上了一杯木瓜牛奶。
这个是啥嘞,我忘了
店主额外赠送的芒果冰沙,很好吃,很大杯,我喜欢芒果。
主食来了。番茄肉酱意粉。因为屋子不是很热,所以这个意粉上来很快就凉了,于是我就吃了一口。
味道还是不错的,番茄味道很浓,还加了香草。
太不环保了,我占用了这么多勺子叉子。
意大利肉酱焗饭
可以拉丝,奶酪分量很足,这个我很喜欢,吃了很多,热乎乎的真给力。
金枪鱼三明治,在家可以给孩子做,很简单的
黑椒牛柳焗饭。我喜欢吃里面的青豆,牛肉很大片,味道特别好,有点辣,好吃,用我们淘宝店主的话就是全五分!
咖喱牛腩饭,咖哩味道不是很大,土豆是刚煮熟的,很绵软,她家的焗饭个个我都很满意。
胡萝卜蛋糕来了,颜色好,营养足,里面还有很多核桃肉呢,香,实惠,能吃饱的蛋糕。
附近景一张。
芝士蛋糕,除了饼底有点坚硬别的无缺点,而且我认为的缺点也只是我个人的观点,哈哈。
巧克力熔岩蛋糕,很香很腻很甜,可惜照片没拍好,影响了它的美貌。
送给大家一只萌兔子,什么时候都保持好心情是最重要的。
四 : 在天才和疯子之间奋斗的一生--JohnNash--博弈论
最近看了关于博弈论的公开课,受益匪浅。约翰.纳什1994年获得诺贝尔经济学奖的时候已经66岁。In game theory, the Nash equilibrium (namedafter John Forbes Nash) is a solution concept of a game involving two or more players, inwhich each player is assumed to know the equilibriumstrategies of the other players, and no player has anything togain by changing only his own strategy unilaterally.[1]:14If each player has chosen a strategy and no player can benefit bychanging his or her strategy while the other players keep theirsunchanged, then the current set of strategy choices and thecorresponding payoffs constitute a Nash equilibrium.
Stated simply, Amy and Phil are in Nash equilibrium if Amy ismaking the best decision she can, taking into account Phil'sdecision, and Phil is making the best decision he can, taking intoaccount Amy's decision. Likewise, a group of players are in Nashequilibrium if each one is making the best decision that he or shecan, taking into account the decisions of the others.
Applications:
Game theorists use the Nash equilibrium concept to analyze theoutcome of the strategic interaction of several decision makers. In other words, it providesa way of predicting what will happen if several people or severalinstitutions are making decisions at the same time, and if theoutcome depends on the decisions of the others. The simple insightunderlying John Nash's idea is that we cannot predict the result ofthe choices of multiple decision makers if we analyze thosedecisions in isolation. Instead, we must ask what each player woulddo, taking into account the decision-making of theothers.
Nash equilibrium has been used to analyze hostile situationslike warand arms races[2](see Prisoner's dilemma), and also howconflict may be mitigated by repeated interaction (see Tit-for-tat). It has also been used to study towhat extent people with different preferences can cooperate (seeBattle of the sexes),and whether they will take risks to achieve a cooperative outcome(see Stag hunt). It has been used to study the adoptionof technical standards[citationneeded], and also the occurrence of bankruns and currency crises (see Coordination game). Other applicationsinclude traffic flow (see Wardrop's principle), how to organizeauctions (see auction theory), the outcome of effortsexerted by multiple parties in the education process,[3]regulatory legislation such as environmental regulations (seeTragedy of theCommons),[4]and even penalty kicks in soccer(see Matching pennies).[5]
History:A version of the Nash equilibrium concept was first used byAntoine Augustin Cournot inhis theory of oligopoly (1838). In Cournot's theory, firms choosehow much output to produce to maximize their own profit. However,the best output for one firm depends on the outputs of others. ACournot equilibrium occurs when eachfirm's output maximizes its profits given the output of the otherfirms, which is a pure strategy Nash Equilibrium.
The modern game-theoretic concept of Nash Equilibrium is insteaddefined in terms of mixed strategies, where players choose aprobability distribution over possible actions. The concept of themixed strategy Nash Equilibrium was introduced by John von Neumann and Oskar Morgenstern in their 1944 book TheTheory of Games and Economic Behavior. However, their analysiswas restricted to the special case of zero-sum games. They showed that a mixed-strategyNash Equilibrium will exist for any zero-sum game with a finite setof actions. The contribution of John Forbes Nash in his 1951 articleNon-Cooperative Games was to define a mixed strategy NashEquilibrium for any game with a finite set of actions and provethat at least one (mixed strategy) Nash Equilibrium must exist insuch a game.
Since the development of the Nash equilibrium concept, gametheorists have discovered that it makes misleading predictions (orfails to make a unique prediction) in certain circumstances.Therefore they have proposed many related solution concepts (also called 'refinements'of Nash equilibrium) designed to overcome perceived flaws in theNash concept. One particularly important issue is that some Nashequilibria may be based on threats that are not 'credible'. Therefore, in 1965 Reinhard Selten proposed subgame perfect equilibrium as arefinement that eliminates equilibria which depend on non-credible threats. Other extensionsof the Nash equilibrium concept have addressed what happens if agame is repeated, or what happens if a game is playedin the absence of perfect information. However,subsequent refinements and extensions of the Nash equilibriumconcept share the main insight on which Nash's concept rests: allequilibrium concepts analyze what choices will be made when eachplayer takes into account the decision-making of others.
Informally, a set of strategies is a Nash equilibrium if noplayer can do better by unilaterally changing his or her strategy.To see what this means, imagine that each player is told thestrategies of the others. Suppose then that each player askshimself or herself: "Knowing the strategies of the other players,and treating the strategies of the other players as set in stone,can I benefit by changing my strategy?"
If any player would answer "Yes", then that set of strategies isnot a Nash equilibrium. But if every player prefers not to switch(or is indifferent between switching and not) then the set ofstrategies is a Nash equilibrium. Thus, each strategy in a Nashequilibrium is a best response to all other strategies in thatequilibrium.[6]
The Nash equilibrium may sometimes appear non-rational in athird-person perspective. This is because it may happen that a Nashequilibrium is not Pareto optimal.
The Nash equilibrium may also have non-rational consequences insequential games because players may "threaten" each other withnon-rational moves. For such games the subgame perfect Nashequilibrium may be more meaningful as a tool of analysis.
Let (S, f) be a game with n players, whereSi is the strategy set for player i,S=S1 × S2 ... × Sn is theset of strategy profiles andf=(f1(x), ..., fn(x)) is the payofffunction for x S. Let xi be a strategy profile of playeri and x-i be a strategy profile of allplayers except for player i. When each player i {1, ..., n} chooses strategy xi resulting instrategy profile x = (x1, ..., xn)then player i obtains payoff fi(x). Notethat the payoff depends on the strategy profile chosen, i.e., onthe strategy chosen by player i as well as the strategieschosen by all the other players. A strategy profilex* S is a Nash equilibrium (NE) if no unilateral deviation instrategy by any single player is profitable for that player, thatis
A game can have either a pure-strategy or a mixed Nash Equilibrium, (in the latter a purestrategy is chosen stochastically with a fixed frequency). Nash proved that if we allow mixed strategies, then everygame with a finite number of players in which each player canchoose from finitely many pure strategies has at least one Nashequilibrium.
When the inequality above holds strictly (with instead of ) for all players and all feasible alternative strategies, thenthe equilibrium is classified as a strict Nash equilibrium.If instead, for some player, there is exact equality between and some other strategy in the set , then the equilibrium is classified as a weak Nashequilibrium.
Nash均衡最浅显易懂的例子就是"囚徒困境":Cooperate | Defect | |
---|---|---|
Cooperate | 3, 3 | 0, 5 |
Defect | 5, 0 | 1, 1 |
The Prisoner's Dilemma has a similar matrix as depicted for theCoordination Game, but the maximum reward for each player (in thiscase, 5) is only obtained when the players' decisions aredifferent. Each player improves his own situation by switching from"Cooperating" to "Defecting," given knowledge that the otherplayer's best decision is to "Defect." The Prisoner's Dilemma thushas a single Nash Equilibrium: both players choosing to defect.
What has long made this an interesting case to study is the factthat this scenario is globally inferior to "Both Cooperating." Thatis, both players would be better off if they both chose to"Cooperate" instead of both choosing to defect. However, eachplayer could improve his own situation by breaking the mutualcooperation, no matter how the other player possibly (or certainly)changes his decision.
Player 2 adopts strategy A | Player 2 adopts strategy B | |
---|---|---|
Player 1 adopts strategy A | 4 / 4 | 1 / 3 |
Player 1 adopts strategy B | 3 / 1 | 2 / 2 |
The coordination game is a classic (symmetric) two player, two strategy game, with an examplepayoff matrix shown to the right. The playersshould thus coordinate, both adopting strategy A, to receive thehighest payoff; i.e., 4. If both players chose strategy B though,there is still a Nash equilibrium. Although each player is awardedless than optimal payoff, neither player has incentive to changestrategy due to a reduction in the immediate payoff (from 2 to1).
A famous example of this type of game was called the Staghunt; in the game two players may choose to hunt a stag or arabbit, the former providing more meat (4 utility units) than thelatter (1 utility unit). The caveat is that the stag must becooperatively hunted, so if one player attempts to hunt the stag,while the other hunts the rabbit, he will fail in hunting (0utility units), whereas if they both hunt it they will split thepayload (2, 2). The game hence exhibits two equilibria at (stag,stag) and (rabbit, rabbit) and hence the players' optimal strategydepend on their expectation on what the other player may do. If onehunter trusts that the other will hunt the stag, he should hunt thestag; however if he suspects that the other will hunt the rabbit,he should hunt the rabbit. This game was used as an analogy forsocial cooperation, since much of the benefit that people gain insociety depends upon people cooperating and implicitly trusting oneanother to act in a manner corresponding with cooperation.
Another example of a coordination game is the setting where twotechnologies are available to two firms with compatible products,and they have to elect a strategy to become the market standard. Ifboth firms agree on the chosen technology, high sales are expectedfor both firms. If the firms do not agree on the standardtechnology, few sales result. Both strategies are Nash equilibriaof the game.
Driving on a road, and having to choose either to drive on theleft or to drive on the right of the road, is also a coordinationgame. For example, with payoffs 100 meaning no crash and 0 meaninga crash, the coordination game can be defined with the followingpayoff matrix:
Drive on the Left | Drive on the Right | |
---|---|---|
Drive on the Left | 100, 100 | 0, 0 |
Drive on the Right | 0, 0 | 100, 100 |
In this case there are two pure strategy Nash equilibria, whenboth choose to either drive on the left or on the right. If weadmit mixed strategies (where a pure strategy ischosen at random, subject to some fixed probability), then thereare three Nash equilibria for the same case: two we have seen fromthe pure-strategy form, where the probabilities are (0%,100%) forplayer one, (0%, 100%) for player two; and (100%, 0%) for playerone, (100%, 0%) for player two respectively. We add another wherethe probabilities for each player is (50%, 50%).
以及基于网络的Nash均衡:
An application of Nash equilibria is in determining the expectedflow of traffic in a network. Consider the graph on the right. Ifwe assume that there are "cars" traveling from A to D, what is the expected distribution oftraffic in the network?
This situation can be modeled as a "game" where every travelerhas a choice of 3 strategies, where each strategy is a route from Ato D (either , , or ). The "payoff" of each strategy is the travel time of each route.In the graph on the right, a car travelling via experiences travel time of , where is the number of cars traveling on edge . Thus, payoffs for any given strategy depend on the choices ofthe other players, as is usual. However, the goal in this case isto minimize travel time, not maximize it. Equilibrium will occurwhen the time on all paths is exactly the same. When that happens,no single driver has any incentive to switch routes, since it canonly add to his/her travel time. For the graph on the right, if,for example, 100 cars are travelling from A to D, then equilibriumwill occur when 25 drivers travel via , 50 via , and 25 via . Every driver now has a total travel time of 3.75.
Notice that this distribution is not, actually, sociallyoptimal. If the 100 cars agreed that 50 travel via and the other 50 through , then travel time for any single car would actually be 3.5 whichis less than 3.75. This is also the Nash equilibrium if the pathbetween B and C is removed, which means that adding an additionalpossible route can decrease the efficiency of the system, aphenomenon known as Braess's Paradox.
Player 2 chooses '0' | Player 2 chooses '1' | Player 2 chooses '2' | Player 2 chooses '3' | |
---|---|---|---|---|
Player 1 chooses '0' | 0,0 | 2, -2 | 2, -2 | 2, -2 |
Player 1 chooses '1' | -2, 2 | 1, 1 | 3,-1 | 3, -1 |
Player 1 chooses '2' | -2, 2 | -1,3 | 2,2 | 4, 0 |
Player 1 chooses '3' | -2, 2 | -1, 3 | 0, 4 | 3, 3 |
This can be illustrated by a two-player game in which bothplayers simultaneously choose an integer from 0 to 3 and they bothwin the smaller of the two numbers in points. In addition, if oneplayer chooses a larger number than the other, then he/she has togive up two points to the other.
This game has a unique pure-strategy Nash equilibrium: bothplayers choosing 0 (highlighted in light red). Any other choice ofstrategies can be improved if one of the players lowers his numberto one less than the other player's number. In the table to theright, for example, when starting at the green square it is inplayer 1's interest to move to the purple square by choosing asmaller number, and it is in player 2's interest to move to theblue square by choosing a smaller number. If the game is modifiedso that the two players win the named amount if they both choosethe same number, and otherwise win nothing, then there are 4 Nashequilibria (0,0...1,1...2,2...and 3,3).
There is an easy numerical way to identify Nash equilibria on apayoff matrix. It is especially helpful in two-person games whereplayers have more than two strategies. In this case formal analysismay become too long. This rule does not apply to the case wheremixed (stochastic) strategies are of interest. The rule goes asfollows: if the first payoff number, in the duplet of the cell, isthe maximum of the column of the cell and if the second number isthe maximum of the row of the cell - then the cell represents aNash equilibrium.
Option A | Option B | Option C | |
---|---|---|---|
Option A | 0, 0 | 25, 40 | 5, 10 |
Option B | 40, 25 | 0, 0 | 5, 15 |
Option C | 10, 5 | 15, 5 | 10, 10 |
We can apply this rule to a 3×3 matrix:
Using the rule, we can very quickly (much faster than withformal analysis) see that the Nash Equilibria cells are (B,A),(A,B), and (C,C). Indeed, for cell (B,A) 40 is the maximum of thefirst column and 25 is the maximum of the second row. For (A,B) 25is the maximum of the second column and 40 is the maximum of thefirst row. Same for cell (C,C). For other cells, either one or bothof the duplet members are not the maximum of the corresponding rowsand columns.
This said, the actual mechanics of finding equilibrium cells isobvious: find the maximum of a column and check if the secondmember of the pair is the maximum of the row. If these conditionsare met, the cell represents a Nash Equilibrium. Check all columnsthis way to find all NE cells. An N×N matrix may have between 0 andN×N pure strategy Nash equilibria.
The concept of stability, useful in the analysis of manykinds of equilibria, can also be applied to Nash equilibria.
A Nash equilibrium for a mixed strategy game is stable if asmall change (specifically, an infinitesimal change) inprobabilities for one player leads to a situation where twoconditions hold:
If these cases are both met, then a player with the small changein his mixed-strategy will return immediately to the Nashequilibrium. The equilibrium is said to be stable. If condition onedoes not hold then the equilibrium is unstable. If only conditionone holds then there are likely to be an infinite number of optimalstrategies for the player who changed. John Nash showed that the latter situationcould not arise in a range of well-defined games.
In the "driving game" example above there are both stable andunstable equilibria. The equilibria involving mixed-strategies with100% probabilities are stable. If either player changes hisprobabilities slightly, they will be both at a disadvantage, andhis opponent will have no reason to change his strategy in turn.The (50%,50%) equilibrium is unstable. If either player changes hisprobabilities, then the other player immediately has a betterstrategy at either (0%, 100%) or (100%, 0%).
Stability is crucial in practical applications of Nashequilibria, since the mixed-strategy of each player is notperfectly known, but has to be inferred from statisticaldistribution of his actions in the game. In this case unstableequilibria are very unlikely to arise in practice, since any minutechange in the proportions of each strategy seen will lead to achange in strategy and the breakdown of the equilibrium.
The Nash equilibrium defines stability only in terms ofunilateral deviations. In cooperative games such a concept is notconvincing enough. Strong Nash equilibrium allows fordeviations by every conceivable coalition.[7]Formally, a Strong Nash equilibrium is a Nashequilibrium in which no coalition, taking the actions of itscomplements as given, can cooperatively deviate in a way thatbenefits all of its members.[8]However, the Strong Nash concept is sometimes perceived as too"strong" in that the environment allows for unlimited privatecommunication. In fact, Strong Nash equilibrium has to be Pareto efficient. As a result of theserequirements, Strong Nash is too rare to be useful in many branchesof game theory. However, in games such as elections with many moreplayers than possible outcomes, it can be more common than a stableequilibrium.
A refined Nash equilibrium known as coalition-proof Nashequilibrium (CPNE)[7]occurs when players cannot do better even if they are allowed tocommunicate and make "self-enforcing" agreement to deviate. Everycorrelated strategy supported by iterated strict dominance and on thePareto frontier is a CPNE.[9]Further, it is possible for a game to have a Nash equilibrium thatis resilient against coalitions less than a specified size, k. CPNEis related to the theory of the core.
Finally in the eighties, building with great depth on such ideasMertens-stable equilibriawere introduced as a solution concept. Mertens stable equilibria satisfy bothforward induction and backward induction. In a Gametheory context stable equilibria now usually refer toMertens stable equilibria.
If a game has a unique Nash equilibrium and is played amongplayers under certain conditions, then the NE strategy set will beadopted. Sufficient conditions to guarantee that the Nashequilibrium is played are:
Examples of game theory problems in which theseconditions are not met:
Due to the limited conditions in which NE can actually beobserved, they are rarely treated as a guide to day-to-daybehaviour, or observed in practice in human negotiations. However,as a theoretical concept in economics and evolutionary biology, the NE hasexplanatory power. The payoff in economics is utility (or sometimesmoney), and in evolutionary biology gene transmission, both are thefundamental bottom line of survival. Researchers who apply gamestheory in these fields claim that strategies failing to maximizethese for whatever reason will be competed out of the market orenvironment, which are ascribed the ability to test all strategies.This conclusion is drawn from the "stability" theory above. In these situationsthe assumption that the strategy observed is actually a NE hasoften been borne out by research[citationneeded].[verificationneeded]
The Nash equilibrium is a superset of the subgame perfect Nashequilibrium. The subgame perfect equilibrium in addition to theNash Equilibrium requires that the strategy also is a Nashequilibrium in every subgame of that game. This eliminates allnon-credible threats, that is,strategies that contain non-rational moves in order to make thecounter-player change his strategy.
The image to the right shows a simple sequential game thatillustrates the issue with subgame imperfect Nash equilibria. Inthis game player one chooses left(L) or right(R), which is followedby player two being called upon to be kind (K) or unkind (U) toplayer one, However, player two only stands to gain from beingunkind if player one goes left. If player one goes right therational player two would de facto be kind to him in that subgame.However, The non-credible threat of being unkind at 2(2) is stillpart of the blue (L, (U,U)) Nash equilibrium. Therefore, ifrational behavior can be expected by both parties the subgameperfect Nash equilibrium may be a more meaningful solution conceptwhen such dynamic inconsistencies arise.
Nash's original proof (in his thesis) used Brouwer's fixed pointtheorem (e.g., see below for a variant). We give a simpler proofvia the Kakutani fixed point theorem,following Nash's 1950 paper (he credits DavidGale with the observation that such a simplification ispossible).
To prove the existence of a Nash Equilibrium, let be the best response of player i to the strategies of all otherplayers.
Here, , where , is a mixed strategy profile in the set of all mixed strategiesand is the payoff function for player i. Define a set-valued function such that . The existence of a Nash Equilibrium is equivalent to having a fixed point.
Kakutani's fixed point theorem guarantees the existence of afixed point if the following four conditions are satisfied.
Condition 1. is satisfied from the fact that is a simplex and thus compact. Convexity follows from players'ability to mix strategies. is nonempty as long as players have strategies.
Condition 2. is satisfied because players maximize expectedpayoffs which is continuous function over a compact set. TheWeierstrass Extreme Value Theorem guarantees thatthere is always a maximum value.
Condition 3. is satisfied as a result of mixed strategies.Suppose , then . i.e. if two strategies maximize payoffs, then a mix between thetwo strategies will yield the same payoff.
Condition 4. is satisfied by way of Berge's maximum theorem. Because is continuous and compact, is upper hemicontinuous.
Therefore, there exists a fixed point in and a Nash Equilibrium.[11]
When Nash made this point to John von Neumann in 1949, von Neumannfamously dismissed it with the words, "That's trivial, you know.That's just a fixed point theorem." (See Nasar,1998, p.94.)
We have a game where is the number of players and is the action set for the players. All of the action sets are finite. Let denote the set of mixed strategies for the players. The finitenessof the s ensures the compactness of .
We can now define the gain functions. For a mixed strategy , we let the gain for player on action be
The gain function represents the benefit a player gets byunilaterally changing his strategy. We now define where
for . We see that
We now use to define as follows. Let
for . It is easy to see that each is a valid mixed strategy in . It is also easy to check that each is a continuous function of , and hence is a continuous function. Now is the cross product of a finite number of compact convex sets,and so we get that is also compact and convex. Therefore we may apply the Brouwerfixed point theorem to . So has a fixed point in , call it .
I claim that is a Nash Equilibrium in . For this purpose, it suffices to show that
This simply states the each player gains no benefit byunilaterally changing his strategy which is exactly the necessarycondition for being a Nash Equilibrium.
Now assume that the gains are not all zero. Therefore, , , and such that . Note then that
So let . Also we shall denote as the gain vector indexed by actions in . Since we clearly have that . Therefore we see that
Since we have that is some positive scaling of the vector . Now I claim that
.To see this, we first note that if then this is true by definition of the gain function. Now assumethat . By our previous statements we have that
and so the left term is zero, giving us that the entireexpression is as needed.
So we finally have that
where the last inequality follows since is a non-zero vector. But this is a clear contradiction, so allthe gains must indeed be zero. Therefore is a Nash Equilibrium for as needed.
If a player A has a dominant strategy then there exists a Nash equilibrium in which A plays . In the case of two players A and B, there exists a Nashequilibrium in which A plays and B plays a best response to . If is a strictly dominant strategy, A plays in all Nash equilibria. If both A and B have strictly dominantstrategies, there exists a unique Nash equilibrium in which eachplays his strictly dominant strategy.
In games with mixed strategy Nash equilibria, the probability ofa player choosing any particular strategy can be computed byassigning a variable to each strategy that represents a fixedprobability for choosing that strategy. In order for a player to bewilling to randomize, his expected payoff for each strategy shouldbe the same. In addition, the sum of the probabilities for eachstrategy of a particular player should be 1. This creates a systemof equations from which the probabilities of choosing each strategycan be derived.[6]
Player B plays H | Player B plays T | |
---|---|---|
Player A plays H | −1, +1 | +1, −1 |
Player A plays T | +1, −1 | −1, +1 |
In the matching pennies game, player A loses a point to B if Aand B play the same strategy and wins a point from B if they playdifferent strategies. To compute the mixed strategy Nashequilibrium, assign A the probability p of playing H and (1−p) ofplaying T, and assign B the probability q of playing H and (1−q) ofplaying T.
Thus a mixed strategy Nash equilibrium in this game is for eachplayer to randomly choose H or T with equal probability.
John Forbes Nash, Jr. | |
---|---|
Born | June13, 1928 (age84) Bluefield, West Virginia,U.S. |
Residence | United States |
Nationality | American |
Fields | Mathematics, Economics |
Institutions | MassachusettsInstitute of Technology Princeton University |
Alma mater | Princeton University, Carnegie Institute ofTechnology (now part of Carnegie Mellon University) |
Doctoral advisor | Albert W. Tucker |
Knownfor | Nash equilibrium Nash embedding theorem Algebraic geometry Partialdifferential equations |
Notable awards | Nobel MemorialPrize in Economic Sciences (1994) |
Spouse | Alicia Lopez-Harrison de Lardé (m. 1957–1963;2001–present) |
John Forbes Nash, Jr. (born June 13, 1928) is an Americanmathematician whose works in gametheory, differential geometry, and partialdifferential equations have provided insight into the forcesthat govern chance and events inside complex systems in daily life.His theories are used in market economics,computing, evolutionary biology, artificial intelligence, accounting,politics and military theory. Serving as a Senior ResearchMathematician at Princeton University during the latterpart of his life, he shared the 1994 Nobel MemorialPrize in Economic Sciences with game theorists Reinhard Selten and John Harsanyi.
Nash is the subject of the Hollywood movie A Beautiful Mind. The film,loosely based on the biography of the same name, focuseson Nash's mathematical genius and struggle with paranoidschizophrenia.[1][2]
In his own words, he states,
Nash was born on June 13, 1928, in Bluefield, West Virginia. Hisfather, after whom he is named, was an electrical engineer for theAppalachian Electric PowerCompany. His mother, born Margaret Virginia Martin and known asVirginia, had been a schoolteacher before she married. Both parentspursued opportunities to supplement their son's education,providing him with encyclopedias and even allowing him to takeadvanced mathematics courses at a local college while still in highschool. After attending Carnegie Institute ofTechnology (now Carnegie Mellon University) andgraduating in 1948 with bachelor's and master's degrees inmathematics, he accepted a scholarship to Princeton Universitywhere he pursued his graduate studies in Mathematics.[3]
Nash's advisor and former Carnegie Tech professor R.J. Duffinwrote a letter of recommendation consisting of a single sentence:"This man is a genius."[4]Nash was accepted by Harvard University, but the chairman ofthe mathematics department of Princeton, Solomon Lefschetz, offered him the John S. Kennedyfellowship, which was enough to convince Nash that Harvard valuedhim less.[5]Thus he went to Princeton where he worked on his equilibrium theory. He earned a doctorate in 1950 with a 28-pagedissertation onnon-cooperative games.[6]The thesis, which was written under the supervision of Albert W. Tucker, contained the definitionand properties of what would later be called the "Nash equilibrium". These studies led to fourarticles:
Nash did ground-breaking work in the area of real algebraic geometry:
His work in mathematics includes the Nash embedding theorem, which showsthat any abstract Riemannian manifold can be isometrically realized as a submanifold of Euclidean space. He also made significantcontributions to the theory of nonlinear parabolic partialdifferential equations and to singularity theory.
In the book A Beautiful Mind, author Sylvia Nasarexplains that Nash was working on proving a theorem involving ellipticpartial differential equations when, in 1956, he suffered a severedisappointment when he learned of an Italian mathematician,Ennio de Giorgi, who had published a proof acouple of months[vague]before Nash achieved his proof. Each took different routes to getto their solutions. The two mathematicians met each other at theCourant Institute of Mathematical Sciences of New York University during the summer of1956. It has been speculated that if only one of them had solvedthe problem, he would have been given the Fields Medal for the proof.[3]
In 2011, the National Security Agencydeclassified letters written by Nash in 1950s, in which he hadproposed a new encryption-decryption machine.[8]The letters show that Nash had anticipated many concepts of moderncryptography, which are based on computationalhardness.[9]
In 1951, Nash went to the MassachusettsInstitute of Technology as a C. L. E. Moore Instructor in themathematics faculty. There, he met Alicia Lopez-Harrison de Lardé(born January 1, 1933), a physicsstudent from El Salvador, whom he married in February1957 at a Catholic ceremony, although Nash was an atheist.[10]She admitted Nash to a mental hospital in 1959for schizophrenia; their son, John Charles MartinNash, was born soon afterward, but remained nameless for a yearbecause his mother felt that her husband should have a say in thename.
Nash and de Lardé divorced in 1963, though after his finalhospital discharge in 1970 Nash lived in de Lardé's house. Theywere remarried in 2001.
Nash has been a longtime resident of West Windsor Township,New Jersey.[11]
Nash began to show signs of extreme paranoia and his wife later described his behavioras erratic, as he began speaking of characters like Charles Hermanand William Parcher who were putting him in danger. Nash seemed tobelieve that all men who wore red ties were part of a communistconspiracy against him. Nash mailed letters to embassies inWashington, D.C., declaring that they wereestablishing a government.[12][13]
He was admitted to the McLean Hospital, April–May 1959, where he wasdiagnosed with paranoidschizophrenia. The clinical picture is dominated by relativelystable, often paranoid, fixed beliefs that are either false,over-imaginative or unrealistic, usually accompanied by experiencesof seemingly real perception of something not actuallypresent— particularly auditory and perceptionaldisturbances, a lack of motivation for life, and mild clinicaldepression.[14]Upon his release, Nash resigned from MIT, withdrew his n,and went to Europe, unsuccessfully seeking political asylum inFrance and East Germany. He tried to renounce his U.S.citizenship. After a problematic stay in Parisand Geneva, he was arrested by the French police anddeported back to the United States at the request of the U.S.government.
In 1961, Nash was committed to the New Jersey State Hospital at Trenton. Over thenext nine years, he spent periods in psychiatric hospitals, where, aside fromreceiving antipsychotic medications, he was administered insulin shock therapy.[14][15][16]
Although he sometimes took prescribed medication, Nash laterwrote that he only ever did so under pressure. After 1970, he wasnever committed to the hospital again and he refused anymedication. According to Nash, the film A Beautiful Mind inaccuratelyimplied that he was taking the new atypical antipsychotics during thisperiod. He attributed the depiction to the screenwriter (whosemother, he notes, was a psychiatrist), who was worried aboutencouraging people with the disorder to stop taking theirmedication.[17]Others, however, have questioned whether the fabrication obscured akey question as to whether recovery from problems like Nash's canactually be hindered by such drugs,[18]and Nash has said they are overrated and that the adverse effectsare not given enough consideration once someone is deemed mentally ill.[19][20][21]According to Sylvia Nasar, author of the book A Beautiful Mind, on which themovie was based, Nash recovered gradually with the passage of time.Encouraged by his then former wife, de Lardé, Nash worked in acommunitarian setting wherehis eccentricities were accepted. De Lardé said of Nash, "it's justa question of living a quiet life".[13]
Nash in November 2006 at a game theory conference in Cologne.Nash dates the start of what he terms "mental disturbances" tothe early months of 1959 when his wife was pregnant. He hasdescribed a process of change "from scientific rationality ofthinking into the delusional thinkingcharacteristic of persons who are psychiatrically diagnosed as'schizophrenic' or 'paranoid schizophrenic'"[22]including seeing himself as a messenger or having a specialfunction in some way, and with supporters and opponents and hiddenschemers, and a feeling of being persecuted, and looking for signsrepresenting divine revelation.[23]Nash has suggested his delusional thinking was related to hisunhappiness and his striving to feel important and be recognized,and to his characteristic way of thinking such that "I wouldn'thave had good scientific ideas if I had thought more normally." Hehas said, "If I felt completely pressureless I don't think I wouldhave gone in this pattern".[24]He does not see a categorical distinction between terms such asschizophrenia and bipolar disorder.[25]Nash reports that he did not hear voices until around 1964, laterengaging in a process of rejecting them.[26]He reports that he was always taken to hospitals against his will,and only temporarily renounced his "dream-like delusionalhypotheses" after being in a hospital long enough to decide tosuperficially conform - to behave normally or to experience"enforced rationality". Only gradually on his own did he"intellectually reject" some of the "delusionally influenced" and"politically-oriented" thinking as a waste of effort. However, by1995, although he was "thinking rationally again in the style thatis characteristic of scientists," he says he also felt morelimited.[22][27]
At Princeton, campus legend Nash became "The Phantom of FineHall" (Princeton's mathematics center), a shadowy figure who wouldscribble arcane equations on blackboards in the middle of thenight. The legend appears in a work of fiction based on Princetonlife, The Mind-Body Problem, by Rebecca Goldstein.
In 1978, Nash was awarded the John von Neumann Theory Prizefor his discovery of non-cooperative equilibria, now calledNash equilibria. He won the Leroy P. Steele Prize in 1999.
In 1994, he received the Nobel MemorialPrize in Economic Sciences (along with John Harsanyi and Reinhard Selten) as a result of his gametheory work as a Princeton graduate student. In the late 1980s,Nash had begun to use email to gradually link with workingmathematicians who realized that he was the John Nash andthat his new work had value. They formed part of the nucleus of agroup that contacted the Bank of Sweden's Nobelaward committee and were able to vouch for Nash's mental healthability to receive the award in recognition of his earlywork.[citationneeded]
As of 2011 Nash's recent work involves ventures in advanced gametheory, including partial agency, which show that, as in his earlycareer, he prefers to select his own path and problems. Between1945 and 1996, he published 23 scientific studies.
Nash has suggested hypotheses on mental illness. He hascompared not thinking in an acceptable manner, or being "insane"and not fitting into a usual social function, to being "on strike" from an economic point of view. He hasadvanced evolutionary psychology views aboutthe value of human diversity and the potential benefits ofapparently nonstandard behaviors or roles.[28]
Nash has developed work on the role of money in society. Withinthe framing theorem that people can be so controlled and motivatedby money that they may not be able to reason rationally about it,he has criticized interest groups that promote quasi-doctrinesbased on Keynesian economics that permitmanipulative short-term inflation and debt tacticsthat ultimately undermine currencies. He has suggested a global"industrial consumption price index" system that would support thedevelopment of more "ideal money" that people could trust ratherthan more unstable "bad money". He notes that some of his thinkingparallels economist and political philosopher Friedrich Hayek's thinking regarding moneyand a nontypical viewpoint of the function of theauthorities.[29][30]
Nash received an honorary degree, Doctor of Science andTechnology, from Carnegie Mellon University in1999, an honorary degree in economics from the University of NaplesFederico II on March 19, 2003,[31]an honorary doctorate in economics from the University ofAntwerp in April 2007, and was keynote speaker at a conferenceon Game Theory. He has also been a prolific guest speaker at anumber of world-class events, such as the Warwick Economics Summit in 2005held at the University of Warwick.
Nash has an Erdős number of 3.[32][33][34]
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