reference:
https://www.runoob.com/nodejs/nodejs-tutorial.html

下载Node.js.xmind

金字塔原理：

自下而上的思考，自上而下的表达。

1. 文章结构中任一层次上的思想必须是其下一层次思想的概括
2. 每一层次的思想要归属于同一范畴
3. 每一层次的思想要按逻辑顺序组织

表达的逻辑

框架的构架

在较高层次的主题之间尽量用归纳法进行论述，在低层次用演绎方式论述。

• 演绎推理：背景(情境)—冲突—问题—解决方案
• 归纳推理：找到一组具体共同思想的名词，识别并剔除该组思想中与其他思想不相称的观点

深入的过程

通过纵向的思想引出主题和子主题之前的纵向关系。

“思想”定义：向读者发出新信息并引发读者疑问的语句。

纵向的思想实质是“疑问/回答”形式，这样更能吸引读者注意力。

序言的结构

以“情境、冲突、疑问、回答”方式来开篇，情境和冲突是读者熟知的事实。通过明确读者最初关心的问题，让后续的内容能吸引读者注意力。

• 标准式： 情境—冲突—解决方案
• 开门见山： 解决方案—情境—冲突
• 突出忧虑： 冲突—情境—解决方案
• 突出信心： 疑问—情境—冲突—解决方案

思考的逻辑（内容的填充）

1. 应用时间顺序、结构顺序、重要程度顺序来构建思考逻辑树
2. 总结句避免使用“缺乏思想”的句子，要说明行动产生的结果或目标
3. 找出各结论之间的共性，得出金字塔尖的结论

四种主要的逻辑顺序：

• 演绎顺序：大前提、小前提、结论—按照演绎推理组织的思想
• 时间顺序：第一、第二、第三—按因果关系组织的思想
• 结构顺序：将整体分割为部分进行评论，划分后的各部分需要符合以下要求：MECE
  • 各部分之间相互独立（mutually exclusive）
  • 所有部分完全穷尽（collectively exhaustive）
• 重要性顺序：最重要、次重要，等等—按类别组织思想

解决问题的逻辑

界定问题：

• 界定问题的框架
• 展开问题的各要素
• 发掘读者的疑问
• 回答疑问

结构化分析问题：

• 设计诊断框架
• 收集信息
• 建立逻辑树（回答是否问题）
• 寻找解决方案

经典:建立诊断框架和逻辑树的指导来分析和引导思维，不仅能提高解决问题的效率，而且还简化了把结果构建成金字塔的工作。无目的的收集资料，会造成60%的无用功！！！

设计诊断框架的方法：其本身呈现有行结构/根据因果关系分解构建/归类分组

Reference:
https://www.jianshu.com/p/bdbf71572911
https://book.douban.com/review/7121761/
https://zhuanlan.zhihu.com/p/78548168

基本数学符号

加减乘除

比较运算符

括号

级数表示

微分和偏微分

其他数学符号

进阶数学符号

代数

指数对数

带参函数

专业课常用符号

高等数学符号

线性代数中的矩阵和向量

其他常用表达式

Reference:
https://mp.weixin.qq.com/s/80Kleej0oO5FNgB10OG8tg

Pearson

要理解Pearson相关系数，首先要理解协方差（Covariance），协方差是一个反映两个随机变量相关程度的指标，如果一个变量跟随着另一个变量同时变大或者变小，那么这两个变量的协方差就是正值，反之相反，公式如下：

$$
\operatorname{cov}(x, y)=\frac{\sum_{i=1}^{n}\left(x_{i}-x_{\mu}\right)\left(y_{i}-y_{\mu}\right)}{n-1}
$$

虽然协方差能反映两个随机变量的相关程度（协方差大于0的时候表示两者正相关，小于0的时候表示两者负相关），但是协方差值的大小并不能很好地度量两个随机变量的关联程度。

为了更好的度量两个随机变量的相关程度，引入了Pearson相关系数，其在协方差的基础上除以了两个随机变量的标准：

$$
\delta^{2}=\frac{\sum_{i=1}^{n}\left(x_{i}-x_{\mu}\right)}{n}
$$

容易得出，pearson是一个介于-1和1之间的值，当两个变量的线性关系增强时，相关系数趋于1或-1；当一个变量增大，另一个变量也增大时，表明它们之间是正相关的，相关系数大于0；如果一个变量增大，另一个变量却减小，表明它们之间是负相关的，相关系数小于0；如果相关系数等于0，表明它们之间不存在线性相关关系。

$$
p_{x, y}=\operatorname{cor}(x, y)=\frac{\operatorname{cov}(x, y)}{\delta x \delta y}=\frac{E\left[\left(x-x_{\mu}\right)\left(y-y_{\mu}\right)\right]}{\delta x \delta y}
$$

Spearman

斯皮尔曼相关性系数，通常也叫斯皮尔曼秩相关系数。“秩”，可以理解成就是一种顺序或者排序，那么它就是根据原始数据的排序位置进行求解，这种表征形式就没有了求皮尔森相关性系数时那些限制。下面来看一下它的计算公式：

$$
\rho_{s}=1-\frac{6 \sum d_{i}^{2}}{n\left(n^{2}-1\right)}
$$

计算过程就是：
对两个变量（X，Y）的数据进行排序（统一用升序或降序），每个变量在排序之后的位置即为其秩次（X’, Y’），原始位置相同的X，Y的秩次X’, Y’的差值即为 $d_i$ 。n是变量的个数（或者对数）。

Kendall

Kendall相关系数是对于定类变量的统计，之前讲pearson是对定距变量的统计，而spearman是对定序变量的统计。

Kendall相关系数的计算公式：

$$
Kendall1=\frac{C-D}{\frac{1}{2} N\left(N-1\right)}
$$

另一个计算公式：

$$
Kendall2=\frac{C-D}{\sqrt{\left(N_{3}-N_{1}\right)\left(N_{3}-N_{2}\right)}}
$$

其中C表示的是两变量中一致性元素的对数，D是不一致性元素的对数。
举例来讲，如果要计算相关性的数据是一个nx2的矩阵M，那么如果 $m_{i,1}$ > $m_{j,1}$ 且 $m_{i,2} > m_{j,2}$，或 $m_{i,1} < m_{j,1}$ 且 $m_{i,2} < m_{j,2}$ ，则称 $m_i$ 和 $m_j$ 构成一个一致性元素对。反之则为不一致性元素对。

第一个和第二个公式的区别在于，当两变量任何一个中都不存在相同元素时用公式1，两变量中任何一个中存在相同元素用2。

其中N为样本数量。再说N3，N2，N1。

$$
\mathrm{N} 3=\frac{1}{2} N(N-1)
$$

N2、N1就比较复杂，它们各指向一个变量，但是计算方法一致：

$$
\mathrm{N} 2=\sum_{i=1}^{s} \frac{1}{2} v_{i}\left(v_{j}-1\right)
$$

s是指该变量中拥有相同元素的小集合的个数，v就是每个集合中元素的个数。

Reference:
https://blog.csdn.net/ichuzhen/article/details/79535226
https://blog.csdn.net/zmqsdu9001/article/details/82840332?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.edu_weight&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-1.edu_weight
https://www.jianshu.com/p/93fd5ab408ae

Something You Shound Not Do

1. 删减、归纳审稿人的意见————有逃避问题的嫌疑
2. 在response中疯狂解释原文内容没问题，不需要修改————存在没有吸取审稿意见的嫌疑
3. 长篇大论、语无伦次的解释————这个问题很大，而且你脑子不清楚
4. 因为不需要回复而隐藏定性评价————其他审稿人发现了会认为：隐藏这部分是因为这些文字对你不利（比如建议reject等）

Tricks

1. 把意见分条，逐条回答
2. 回复时指出修改内容对应文中的章节和位置
3. 针对大部分问题，类似创新性不强、相关性不够、某一部分没讲清楚等等，都可以用以下三段式
   1. 谢谢你的意见
   2. 是我们没写清楚
   3. 我们已经加强了相关部分，把口口口口强调出来。本文的口口口口就在于…
4. 审稿人认为你引文不够，分两种情况
   1. 你引文确实不够————那就老老实实加
   2. 审稿人定向推荐了几篇论文————那就老老实实帮他增加引用量吧
5. 审稿人要求补实验
   1. 补了，且结果有用，加进去
   2. 补了，且结果没用，说明情况并讨论原因
   3. 补不了，但有必要，根据具体原因找替代方案
   4. 补不了，但没必要，还是要找替代方案，不能让审稿人觉得你怂了

reference:
http://blog.sciencenet.cn/blog-71964-1181769.html

遇见心理学，看清真实的自己

1. 看到“鬼”了，大多数情况下是视觉后效
2. 梦境反应的是潜意识
3. 经常与自己沟通，心理暗示远远比你想象的更重要

解读心理学，心理无时不在被“出卖”

微表情

眼睛

1. 眼球左上：回忆
2. 眼球左下：思考，与自己对话
3. 眼球右上：创造视觉想象（说谎）
4. 眼球右下：感受情感、触觉
5. 眼球向左、向右平视：思考，弄懂别人的话
6. 眨眼频率先变快后变慢：很有可能在说假话
7. 长时间凝视对方：极度自信，目空一切

眉毛

1. 眉毛上扬：积极情绪
2. 皱眉：防护性、侵略性
3. 耸眉：不愉快、无可奈何

鼻子

1. 鼻孔长大：兴奋、紧张、恐惧
2. 鼻头冒汗：焦躁、紧张
3. 鼻子提起：轻蔑

嘴巴

1. 咬嘴唇：认真、专注
2. 缩拢嘴唇：否定
3. 嘴角上扬/下拉：高兴/沮丧
4. 嘴唇圆满呈现：放松
5. 嘴唇闭起来：紧张

微行为

头部

1. 抬头：有意投入
2. 低头：谦卑、害羞
3. 点头/摇头：同意/否定
4. 歪头：示弱（头和脸向一侧歪，露出脖颈）、怀疑（下巴向一侧歪）
5. 猛然上扬：惊讶
6. 僵直：无畏或者无聊

舌头

1. 吐舌头：专注，或是为了缓解紧张以表示准备完毕
2. 舔嘴唇：压力大
3. 露出舌尖：调皮

手

1. 尖塔式：自信
2. 交叉式：压力、焦虑
3. 竖起大拇指：优越感
4. 双手摊开：真诚、坦率
5. 双手紧握：显示力量、安全感
6. 双手插兜：不打算行动
7. 双手冻结（手部动作大大减少）：精神紧张，大概率在说谎
8. 搓手、摩拳擦掌：期待、自信
9. 摸鼻子：内心换乱，紧张
10. 摸下巴：自我安慰
11. 摸耳朵：紧张、抗拒、说谎，说话喜欢摸耳朵的人通常心思超极细腻

手臂

1. 收紧或合于身前：防御
2. 手臂挥动：高兴
3. 手臂下沉：消极情绪
4. 张开双臂：放松
5. 背在身后：自信
6. 叉腰：维护权威
7. 双手抱头，打开手臂：投降，或者极度放松、声明统治权

腿

1. 双腿抖动：兴奋、高兴
2. 双腿交叉：放松、自信
3. 跷二郎腿：舒服、自信
4. 双腿分开站立：有信心、膨胀
5. 脚踝相扣：克制情绪、隐藏信息
6. 双脚转向：期望离开
7. 脚跟着地、脚尖上翘：心情很好
8. 双脚冻结：遇到威胁

色彩心理学

色彩使用的讲究

1. 色彩的温度：有冷到暖->蓝色，绿色，紫色，黄色，红色
2. 色彩的重量：搬家用浅色的白箱，保险柜用深色的黑箱
3. 色彩的距离感：蓝色的汽车遇到的追尾事故比红色的汽车要多，因为冷色系让人感觉更远
4. 色彩的时间感：浅色让人感觉到的时间变慢，深色让人感觉到的时间变快

色彩代表的性格

1. 红色：行动者
2. 蓝色：思想者
3. 黄色：领导者
4. 绿色：和平主义者

情绪心理学

情绪定律

人在情绪高涨的时候，看什么都顺眼，做什么都顺手；人在情绪低落的时候，做什么都不顺手，做什么都别扭。

给自己的坏情绪找个排泄的出口

• 补偿法：用新的目标代替原本失败的目标
• 发泄法：语言上的发泄或者肢体上的发泄

成功心理学：成功是可以“想”出来的

让成功的信念破土而出

贝尔效应：时刻强化自己的成功意识

人们只要想着成功，成功的景象就会出现在心中。

舍恩定理：胸怀必胜的信念

新思想只有在真正相信它、对它着迷的人手中，才可以开怀结果。

詹森效应：摒弃杂念，别让自己发挥失常

平时表现良好，但因为没有足够的心理准备而在关键比赛场合失败的现象。

向着成功的目标前进

手表效应：朝着一个目标前行才会更专注

每个人都不能同时挑选两种或两种以上的行为准则或者目标信念，否则他的工作和生活很快就会陷入混乱。

自我选择效应：三年前的选择决定你的今天

我们今天的选择将决定我们三年后的生活，什么样的选择会产生什么样的结果。

客服半途效应：大目标，小步子

当一个人对某一特定目标的追求进行到一半时，通常会对自己能否完成最终目标而产生怀疑，甚至对完成这一目标的意义产生怀疑。

执着心理：不要停止，从开始一直走到最后

执着能让我们获得更多的机会，执着能让我们的行为受到钦佩，执着能让我们距离成功更近一步。

走出思维局限，把握成功机遇

墨菲定律：成功都伴随着错误发生

事情如果有变坏的可能，不过这种可能性有多小，它总会发生，并造成最大可能的破坏。

约拿情结：畏首畏尾将一事无成

期待机会，却又恐惧机会，对迎面而来的机会感到恐惧。

避免塞里格曼效应：冷静面对失败的定居

因失败而产生的绝望、抑郁和意志消沉。

瓦拉赫效应：要懂得经营自己的长处

每个人都不可能是全才，每个人都有其独特的优势和劣势，只要让一个人的优势得到充分的发挥，他一定能够取得惊人的成绩。

避免竞争优势效应：合作才能共赢

通常来说，在双方有共同利益的时候，人们都会优先选择竞争，而不是选择对双方都有利的合作。

社交心理学：相逢即是缘，四海皆兄弟

轻松吸引他人的秘诀

首因效应：第一印象是重头戏

人们第一次与某物或某人接触时会给对方留下深刻的印象。

真诚原则：没有真诚，就会丧失一切

人与人相遇靠的是一点缘分，人与人相处靠的则是一份诚意。

南风法则：“热情”让你轻松走进他人心中

南风法则也叫温暖法则，它源于法国作家拉·封丹的一则寓言：南风的温暖比北风的凌冽更容易让人脱下大衣。

亲和效应：学会成为他人的“自己人”

在人们的交际过程中，如果彼此间存在着某种共同之处或者相似的地方，那么双方就更容易互相接近，也更容易萌生亲密感。

暴露缺点效应：有一些小缺点比完美更好

一个人往往会因为有些小小的缺点，而显得更加可敬可爱。

有效互动，缩短彼此间的距离

自我暴露原则：适度袒露心声，增进彼此感情

良好的人际关系是在双方间自我爆率逐渐增加的过程中发展起来的。

同情效应：亮“辛酸史”，用悲情牌套近乎

同情容易引起好感

倾听定律：“听”比“说”更重要

人们对自己的关注大多胜于他人，所以如果你想进入他人的世界，获得他人的认可，就要学会关注他人。

跷跷板定律：投桃报李，礼尚往来

要让对方高一些，就必须使自己低一些；要让自己高一些，就必须使对方低一些。

频率原则：见面长不如常见面

见面频率低的朋友远不如见面频率高的朋友间的情谊深。

刺猬法则：拿捏好彼此间的最佳距离

刺猬彼此靠近取暖，但是距离太近又会被刺痛。

化解问题和冲突的黄金法则

登门槛效应：步步为营，登入对方心境

一个人若是接受了他人提出的一个小要求后，他会更容易接受后续更高的要求。

无声定律：在适当的时候保持沉默

沉默可以给人一种特别的压力，让对方望而却步，从而在适当的时候化解矛盾和冲突。

留面子效应：处处要给别人留面子

先提出一个大要求，在被拒绝之后，再提出小要求，小要求被接受的可能性更高。

换位思考：用换位思维“化敌为友”

站在对方的立场上去体验和思考问题。

标签效应：给自己贴上宽容的标签

人们一旦被贴上某种标签，就会成为标签所标定的人。

职场心理学：左右逢源，叱咤职场

求职第一步，把握好面试的关键时刻

杜根定律：用自信的明灯展现你的风采

强者不一定是胜利者，但胜利迟早都属于那些有信心的人。

避免羊群效应：不盲从，不打无准备之仗

全面认识自己，知己知彼，摆脱盲从的误区。

近因效应：应变能力不容忽视

人们识记一系列事物时，通常末尾部分形成的记忆最强烈。

脚踏实地，做一个受欢迎的职场人士

路径依赖法则：职场的第一步决定成败

人们一旦选择进入某一路径，无论这一路径是好是坏，惯性的力量会使这一选择不断自我强化，让其轻易走不出去。

蘑菇定律：成蝶需先破茧

人们在刚刚步入某一领域时，常常在一段时间内完全被置于自生自灭的状态下。

榜样效应：三人行，必有我师

在心中梳理某方面的榜样有助于我们梳理正确的人生理想。

冷热水效应：学会调控他人的心理期待

同样一杯温水，如果摸之前先摸了冷水，会觉得更热；如果摸之前先摸了热水，会觉得更冷。

突破心理关，掌控好你的工作节奏

杜利奥定理：时刻保持工作热情

没有什么比市区热忱更使人觉得垂垂老矣。精神状态不佳，一切都将处于不佳状态。

齐加尼克效应：提高效率，适时放松

第一天的工作没有做完，在休息时间，也会出现心里紧张状态。

酝酿效应：遇到难题，歇一歇

不知道从何下手的事情，搁置一段时间后会忽然茅塞顿开。

发挥优势，推动职业生涯发展

青蛙效应：安逸是晋升最大的“敌人”

温水煮青蛙，安逸不仅能让我们忽略周围环境的变化，还会让我们失去很多机会。

避免升职负效应：戒骄戒躁，升职先升值

如果水平不够提前升值，容易出现：

1. 未及时改变时间规划，疲于奔命，总感觉时间不够用
2. 升值后故步自封，不再有更长远的职业规划

管理心理学：一呼百应的管理秘诀

以人为本，赢得员工的心

雷尼尔效应：增强自身的感召力

因为可以从华盛顿大学食堂看到雷尼尔山峰，教授们就算工资低一些也愿意在这里工作。

马斯洛需求层次理论

胜利需求、安全需求、归属与爱的需求、尊重需求、自我实现需求。

避免刻板效应：沟通让管理更顺畅

刻板效应又叫定型效应，道听途说或者先入为主的想法都会使你的认知与真实情况产生极大的偏差。因此，经常与下属沟通至关重要。

保龄球效应：赞美比批评更有效

多看事情的正面，不断的表扬，会使人进步更快。

管理有术，让每位员工发挥最大的潜能

罗森塔尔效应：用积极暗示激发员工自信

向一个人传递积极的期望，他就会进步得更快，发展得更好。

需求激励理论：掌握员工需求，用心去激励

成就需要、权利需要、友谊需要。

鲶鱼效应：加强员工竞争意识，提升企业活力

鲶鱼会捕食沙丁鱼，在沙丁鱼的鱼槽中放入一条鲶鱼，会使沙丁鱼保持活力。

马蝇效应：对症下药，投其所好

因为有压力，所以有动力。

气质学理论：让合适的人做合适的事

• 胆汁质：精力旺盛，勇敢果断
• 多血质：活泼好动，情感外露
• 粘液质：沉稳，有耐心，自信心强
• 抑郁质：稳定情感产生很慢，但对情感的体验深刻、有力、持久，且具有高度的情绪易感性

运筹帷幄，打造一个卓越的团队

热炉效应：严格按照公司制度办事

热炉效应形象地阐述了企业的惩处原则，即警告性原则、一致性原则、及时性原则、公平性原则。

苛希纳定律：化繁为简，加强核心竞争力

有时管理人员越多，工作效率反而越差。

责任分散效应：职责分明，责任到人才有效

在处理一件事时，如果要求多个个体共同完成，每个个体的责任感就会变弱，也叫做旁观者效应。

销售心理学：绝对成交的销售谋略

1. 250定律：每一位客户身后都会有大约250位亲朋好友
2. 哈默定律：不仅抓住客户的显性需求，还会替客户深度挖掘隐性需求
3. 跨栏定律：不断打破自己的销售记录
4. 移情效应：爱屋及乌
5. 兴趣效应：志趣相投的人之间更容易熟识并建立起融洽的关系
6. 赞美效应：人类最基本的共同点，就是渴望被别人赞美，以及成为重要人物的欲望
7. 80/20法则：80%的业务来自20%的客户
8. 博内特定律：要想占领市场的销售份额，首先要占领人们的头脑，占领了人们的头脑，就获得了人们足够的注意力
9. 互惠原理：亏欠感让客户想你靠拢
10. 二选一法则：不要让客户选择要不要，让客户选要这个还是要那个
11. 逆反心理：越不卖，客户越要买（饥饿营销）
12. 名人效应：沾名人的光，商品卖得更好

The Process of a Bitcoin Transaction

Suppose that Alice is transferring 8 bitcoins to Bob, the process goes like this:

1. To initiate a Bitcoin transaction, Alice needs to have: address, private key, wallet
2. Alice signs her bitcoins in the wallet using the private key, transfers to Bob to initiate a transaction
3. Through the Internet, the transaction information start to broadcast to nodes on bitcoin-net
4. A node packs the transaction into the candidate block and starts hash calculation, which is called mining, to win the bookkeeping right
5. A node successfully mines, broadcasts to the whole network, generates new blocks and adds them to the end of the chain
6. Each node acknowledges that it will continue to add blocks after former ones. Mining nodes receive bitcoin rewards. Generally, the transaction is permanently retained after 6 blocks are added
7. Bob gets transferred bitcoins (expressed as UTXO of the transaction)

Five Key Technologies

In order to achieve a successful bitcoin transaction, the following five key technologies are needed:

• Distributed ledger and decentralized network
• Unused transaction output (UTXO)
• The data structure of bitcoin blockchain
• Proof of workload consensus mechanism
• Bitcoin mining mechanism and generation mechanism

Distributed ledger and decentralized network

Bitcoin network does not have a central server. It is composed of many full nodes and light nodes. Among them:

• Full nodes contain block data of all bitcoin blockchains;
• Light nodes only include data related to them.

Compared to traditional centralized transaction system, the Bitcoin uses a distributed ledger in which users open “accounts,” strictly speaking, addresses. Everyone can set up an “account” on the bitcoin blockchain and get a pair of a public key and a private key. The address is the hash value of the public key. We interact with the address through the private key.

Each of us has a wallet, which stores a private key. When two people transfer bitcoin to each other, they can do it directly through their wallet software.

Here, the decentralization of bitcoin is reflected in the fact that there is no longer a centralized organization for centralized management of ledgers. The account books are stored in the decentralized network composed of many nodes; there is no longer a centralized organization to help us manage accounts and deal with transactions. Everyone manages their own wallets, and the transactions are recorded by the distributed account books.

Some people will ask whether the bitcoin in our address is recorded in the account book or whether there seems to be a “centre” to store our assets. In fact, this ledger is stored in the decentralized network in a distributed way, so from this perspective, it can be seen as decentralized.

In contrast, for centralized online payment systems, centralized servers usually manage centralized ledgers. For the bitcoin system, the system behind it is a decentralized network, and network nodes jointly maintain a distributed ledger.

(to be continued)

What is decentralization

Here we illustrate it by means of comparison.

There have always been three forms of “currency” in the digital world:

• Centralized online payment: Paypal, Alipay, Apple Pay…
• Centralized computer points or Internet points: Game coins…
• Decentralized e-cash: Bitcoin, ETH…

Comparison of three forms and cash in the physical world:

The relationship between three forms and cash in the physical world:

What is the decentralization of Bitcoin

From the shallower to the deeper, it has the following aspects:

1. Decentralization of transactions (Automatic)
2. Decentralization of transactions (Autonomous)
3. Decentralization of issuance (Automatic)
4. Decentralization of issuance (Autonomous)
5. Partial decentralization of network (Distributed network)
6. Decentralization of network (Fully open, non-trust-based)
7. Coordinated community (Coordinated and managed by people)
8. Completely decentralized community (Autonomous achieved by mechanism)

Later, in the process of developing and applying blockchain technology, we have to adjust from the most extreme ideal state to the practical direction.

Most blockchain projects are now managed by foundations. For example, Ethereum is co-ordinated between founder Vitalik Butlin and the Ethereum foundation, rather than being fully autonomous as the bitcoin community.

How does blockchain decentralize bitcoin

Main design principles of blockchain system:

• A true point-to-point e-cash should allow direct online payments from the originator to the other party without the need to go through a third party financial institution.
• Although the existing digital signature technology provides some solutions, if a trusted third-party organization is needed to prevent “double payment”, the main benefits (Brought by e-cash) will be lost.
• To solve the problem of “double payment” in e-cash, we provide a solution with point-to-point network technology.
• The network stamps the transaction records, hashes the transaction records, and merges them into a growing chain, which is composed of hash based proof of work. If we don’t redo the proof of work, the records can’t be changed.
• The longest chain is not just proof of the sequence of events observed, but also proof that it is generated by the largest pool of CPU processing power. As long as the computer nodes that control most CPU processing power don’t attack the network itself (with the attacker), they will generate the longest chain, leaving the attacker behind.
• The network itself needs only the simplest structure. The information can be broadcast in the whole network as much as possible. The node can leave and rejoin the network at any time, only need (when rejoining) take the longest workload proof chain as the proof of the transaction occurred during the offline period of the node.

Four key features by William Mougayar:

1. Point to point electronic transactions;
2. No need for financial institutions;
3. Encrypting evidence rather than centralized credit;
4. Credit exists in the network, not in a central institution.

Five key points of bitcoin system design:

Decentralized point-to-point e-cash system

What bitcoin needs to do is a “point-to-point e-cash system”, in which the sender and the receiver deal directly without the intervention of intermediaries.

In order to remove the trusted third party and other intermediaries, we need to solve the “double blossom problem”. In the summary, Nakamoto presents a point-to-point network solution, and introduces the core of the solution - blockchain. He didn’t mention the word block chain, but in the paper he mentioned the two concepts of block and chain respectively.

Distributed ledger

The blockchain of bitcoin is a data block with time stamp and data storage and a chain connected by hash pointer based on workload proof.

This chain, or ledger, is stored on nodes of bitcoin network in a distributed way, so it is also called distributed ledger.

Proof of workload

Nodes in bitcoin network perform encryption hash calculation according to rules to compete for the right to generate new blocks. After the node wins the competition, it gets the bookkeeping right. When it generates a block and becomes the latest block, it gets the mining reward corresponding to the new block.

Workload proof is also the security mechanism of blockchain account book. This chain cannot be modified without redoing the large amount of calculation required by “proof of workload”, which ensures the reliability of the data on the blockchain.

Longest chain principle

At any moment, the longest chain is the final record accepted by all.

Since the longest chain is completed by the main computing power in the network, as long as they do not cooperate with attackers, the longest chain they generate is reliable. This principle is called the “longest chain principle”.

Decentralized network

Bitcoin’s decentralized network architecture is very simple and requires very little infrastructure. It can run on the Internet network. Computer nodes can leave or join the decentralized network at any time. When they join, they only need to follow the longest chain principle.

reference:
http://c.biancheng.net/view/1889.html

Brief History

• 1983, David Chaum first proposed to use encryption technology in digital cash
• 1998, Wei Dai’s B coin first introduced the idea of creating currency by solving calculation problems and decentralized consensus, but the proposal did not give a specific method to achieve decentralized consensus.
• 2005, Hal Finney introduced the concept of “reusable proof of work” (RPOW), which uses the idea of b-coin and the hash cash problem proposed by Adam Baker to create cryptology currency. However, this concept is once again lost in idealization because it relies on trusted computing as the back end.
• May/2007, Nakamoto Satoshi started the Bitcoin project
• August/2008, Nakamoto Satoshi registered domain name bitcoin.org
• 31/Obtober/2008, Nakamoto Satoshi sent an email to all members of a cryptography mailing list entitled “bitcoin: peer-to-peer e-cash thesis.”
• 16/November/2008, Nakamoto Satoshi announced the source code of bitcoin system
• 3/January/2009, Nakamoto Satoshi launched Bitcoin network on the Internet
• 22/May/2010, Bitcoin pizza Festival, one programmer traded 10,000 bitcoins for two great John pizza coupons. For the first time, bitcoin had a fair price: 10000 bitcoins cost $25
• November/2011, Nakamoto Satoshi disappeared

Why Bitcoin

1. Disintermediation: E-cash between individuals with no intervention of a trusted third-party intermediary
2. Decentralization: This e-cash currency issuance does not need a centralized institution, but is completed by the code and community consensus

Why dose Bit coin need Block Chain

In the digital world, if we want to create a disintermediated and decentralized “e-cash”, we also need to design a complete financial system.

This system should be able to solve a series of problems as follows:

• How can this “cash” be issued fairly and impartially without being controlled by any centralized institution or individual?
• How to realize that just like in the physical world, one person can hand the cash directly to another person without any intermediary assistance?
• How to “prevent counterfeiting” this kind of e-cash? Or how can an e-cash not be spent twice?

To solve the problems, Nakamoto developed Bitcoin system, which consists of 3 layers:

1. Application layer. The top layer is bitcoin. This is the application layer of the whole system.
2. Application protocol layer. The function of the middle layer is to issue bitcoin and handle the bitcoin transfer between users. This layer, also known as bitcoin protocol, is the application protocol layer of the whole system.
   1. Application layer. Transfer and bookkeeping functions
   2. Incentive layer. Issuance mechanism and distribution mechanism
   3. Consensus layer. POW(Proof Of Work)
3. General protocol layer. At the bottom are bitcoin’s distributed ledgers and decentralized networks. This layer, also known as bitcoin blockchain, is the general protocol layer of the whole system.
   1. Network layer. P2P mechanism, broadcast mechanism, and verification mechanism
   2. Data layer. Block data(Hash), chain structure(Merkle Tree), and digital signature(Asymmetric encryption)

In the design of bitcoin system, Nakamoto creatively combines computer computing power competition with economic incentives to form a proof of work (POW) consensus mechanism, which enables mining computer nodes to complete the function of currency issuance and accounting in the calculation competition, as well as the operation and maintenance of blockchain ledger and decentralized network.

This forms a complete cycle: the mining machine mining (calculation power competition), the completion of decentralized accounting (operation system), and the economic incentive (economic reward) in the form of bitcoin.

Bitcoin’s workload proof consensus mechanism is a connecting layer, connecting the upper application and the lower technology: the upper layer is the issuance, transfer and anti-counterfeiting of e-cash; the lower layer is the node to the central network to reach an agreement and update the distributed ledger.

Definition of Blockchain

Blockchain is the technology of “value representation” and “value transfer” in the digital world. One side of blockchain coin is the encrypted digital currency or token representing value, and the other side is the distributed ledger and decentralized network for value transfer.

Blockchain is an underlying technology derived from bitcoin. In other words, bitcoin is the first successful application of blockchain technology.

When people talk about Blockchain, what do they mean:

1. Blockchain refers to the data structure of bitcoin, that is, the chain formed by the connection of data blocks, which is also known as “distributed ledger”. In the bitcoin white paper, Nakamoto mentioned block and chain respectively, but later they were combined into the new term block chain.
2. Blockchain refers to the combination of bitcoin’s distributed ledger and decentralized network. Corresponding to bitcoin system, it refers to the whole third layer of bitcoin blockchain.
3. Blockchain refers to the combination of the second layer (bitcoin protocol) and the third layer (bitcoin blockchain) of bitcoin system. It includes distributed ledgers, decentralized networks and bitcoin protocols.
4. Blockchain refers to the whole bitcoin system, including all three layers, including bitcoin with value representation and the whole system behind it. From this perspective, blockchain is regarded as a complete system including both technical and economic parts.

When referring to blockchain, ordinary people often refers to the fourth largest scope, namely “account book + Network + protocol + currency”. In the industry, when people refer to blockchain, they usually refer to the third scope, namely “account book + Network + Protocol”. When talking about blockchain, many software developers usually refer to the second range of “ledger + network”.

reference:
http://c.biancheng.net/view/1884.html

An evaluation index system refers to an organic whole with an internal structure composed of multiple indicators that characterize various aspects of the evaluation object and their interconnections.

Principles to be followed

In order to make the indicator system scientific and standardized, the following principles should be followed when constructing it:

1. Systematic principle. There should be a certain logical relationship between the indicators. They should not only reflect the main characteristics and states of the ecological, economic and social subsystems from different aspects, but also reflect the internal relationship between the ecological, economic and social systems. Each subsystem is composed of a set of indicators, which are independent of each other and connected with each other to form an organic unity. The construction of the index system is hierarchical, from the top to the bottom, from the macro level to the micro level, forming an indivisible evaluation system.
2. Typical principle. It is necessary to ensure that the evaluation indicators have certain typical representativeness, and reflect the comprehensive characteristics of the environment, economy and social changes in a specific region as accurately as possible. Even if the number of indicators is reduced, it is also necessary to facilitate data calculation and improve the reliability of the results. In addition, the setting of evaluation index system, the distribution of weight among indexes and the division of evaluation standard should be adapted to the natural and socio-economic conditions of a specific region.
3. Dynamic principle. The interactive development of ecology, economy and social benefits can only be reflected through certain time scale indicators. Therefore, dynamic changes should be fully considered in the selection of indicators, and the change values of several years should be collected.
4. Concise and scientific principle. The design of each index system and the selection of evaluation indexes must be based on the principle of scientificity, which can objectively and truly reflect the characteristics and conditions of Gaoxigou’s environmental, economic and social development, and can objectively and comprehensively reflect the real relationship between each index. Each evaluation index should be typical, not too many and too detailed, so that the index is too cumbersome and overlapping, and the index cannot be too few and too simple, so as to avoid the omission of index information, errors and untrue phenomena, and the data is easy to obtain and the calculation method is simple and easy to understand.
5. Comparable, operable and quantifiable principle. In terms of indicator selection, special attention should be paid to the consistency within the overall scope. The construction of indicator system serves for the formulation of field assessment and scientific management. The calculation measures and calculation methods of indicator selection must be consistent and unified. Each indicator should be as simple and clear as possible, micro and easy to collect. Each indicator should be highly practical, operable and comparable. In addition, when selecting indicators, it is also necessary to consider whether quantitative processing can be carried out to facilitate mathematical calculation and analysis.
6. Comprehensive principle. At the corresponding evaluation level, the factors affecting the environment, economy and social system are comprehensively considered, and comprehensive analysis and evaluation are carried out.

Features that should be possessed

And the constructed index system should possess these features:

1. Perform a clear guidance direction
2. Quantitative based and qualitative supplemented
3. Difference classification considered

General construction process

1. Building the theoretical foundation
2. Provide empirical evidence
   1. Statistical data support
   2. Evidence from typical cases
   3. Reasonable interpretation of contradictory cases
3. Verify operability

Representative evaluation system: 3E

3E theory refers to:

• Efficacy, which measures its own output
• Efficiency, which reflects the utilization of resources
• Effectiveness, which reflects the effect of the system output on its superior system

3E system represents the trend of diversified development of performance evaluation system. Through the establishment of 3E standard system, the soft environment evaluation system is more scientific and transparent, and the efficiency and operability of performance evaluation are increased, which greatly promotes the improvement and development of public policy evaluation system.