Better Buy: AMD vs. Micron Technology

 Here is the link.

The semiconductor sector has outperformed the broader stock market so far this year, as demand for chips remains strong amid the economic damage done by the coronavirus pandemic. Not surprisingly, chipmakers such as Advanced Micro Devices (NASDAQ:AMD) have stepped on the gas and delivered impressive gains so far in 2020. At the same time, other companies, such as memory and storage company Micron Technology (NASDAQ:MU), have disappointed investors, despite the favorable environment prevailing in the semiconductor industry.

While AMD has benefited from an increase in demand for graphics cards, computer processors, and server chips, Micron has been contending with uncertainty in the memory industry, which was struggling due to oversupply before the pandemic arrived. So does this mean that investors should dump Micron Technology shares to go long on AMD?

My notes:

1. Memory chips should continue to be in good demand thanks to catalysts such as data centers, smartphones, and gaming consoles. 
2. According to data from DRAMeXchange, the price of an 8GB DDR4 DRAM in June stood at $3.31 -- the same as in May. The prices rose consistently from December 2019 until May, indicating that the price gains Micron has been enjoying so far may have come to a halt.

There are two factors that have helped Micron stage this impressive comeback: an uptick in memory demand and improved pricing. In the third quarter, Micron's DRAM (dynamic random access memory) shipments were up 10% sequentially, while average selling prices (ASPs) increased in the mid-single digits. Shipments of NAND flash also increased in the lower single digits quarter over quarter, while ASPs were up in the upper single digits.

Memory chips should continue to be in good demand thanks to catalysts such as data centers, smartphones, and gaming consoles. At the same time, investors need to keep an eye on the supply side as well. An oversupply in the industry sent prices crashing after two solid years in 2017 and 2018, and there are a few ominous signs already that investors need to worry about.

According to data from DRAMeXchange, the price of an 8GB DDR4 DRAM in June stood at $3.31 -- the same as in May. The prices rose consistently from December 2019 until May, indicating that the price gains Micron has been enjoying so far may have come to a halt. The report also points out that spot DRAM prices have dropped 17% over the past three months, and they are expected to drop in the ongoing quarter as well.

Both server and PC DRAM prices are expected to lose momentum as buyers are reportedly holding back purchases in anticipation of a drop in prices. So Micron Technology may have delivered a terrific quarterly report and guidance last month, but the uncertainty around memory prices could play spoilsport.

CVI stock: over 9% dividend -

 I made purchase of CVI stock 10 share on June 8, 2020. 

2020 Year of Crisis: Markets Melt Up

 Here is the link. 

WDC stock: Another 8% drop

 August 20, 2020

Introduction

It is my best place to learn how to invest using my Ameritrade.com retirement account. I like to look into WDC stock. 

My position

I made purchase when earning day over 10% drop, and now it has another 8% loss. I like to see if I should purchase more WDC stock or stock from its competitors. 

I made purchase on August 7, 2020, 100 share WDC at price $37.39.

Why The NAND Industry May Be Heading For Another Downturn That Could Last Longer This Time Around For Western Digital

 Here is the article. 

WDC reported sizable gains in revenue and net income, but earnings call revelations caused the stock to drop nonetheless.

WDC sees weakness ahead in cloud data center demand, a bright spot in prior quarters.

WDC anticipates another downturn in the storage industry and getting out of it may not be so straightforward this time due to several factors.

WDC and the NAND industry may have to deal with a price war to reduce the number of competitors.

Bloomberg Special Report: The Bankruptcy Breakdown

 Here is the link. 

2020 Economy is Being Driven by Central Banks | Ray Dalio Interview

 Here is the link. 

Ray Dalio discusses his views on the global economy and the new role that Central Banks are having in the Economy. Recorded in July 2020. Raymond Thomas Dalio is an American billionaire hedge fund manager and philanthropist who has served as co-chief investment officer of Bridgewater Associates since 1985. He founded Bridgewater in 1975 in New York. Within ten years, it was infused with a US$5 million investment from the World Bank's retirement fund.

Stock investor: How to learn properly from my mistakes?

 August 20, 2020

Introduction

As an investor, I started to invest individual stocks from March 27, 2020. I learned the first mistake to purchase $13,000 at SPX 3300, and a lot of stocks I owned went down over 20 to 40% after my purchase on June 8, 2020. I know that how danger it is to purchase stocks. 

My plan 

I was afraid to invest using my TFSA account with my savings last 10 years. I have to be very responsible. One of ideas is to invest into a few stocks to get 10% rebound, I thought about Canada airline stock, and I think that it is much safe since it is not inflated as other stocks like TSLA, SHOP. 

But I am a beginner, I do not know how to calculate the risk properly. 

Ray Dalio Screams: The Stock Market Is Rigged!

 Here is the article. 

Here are highlights for me to learn from:

1. Central banks and the coordination with the central government - market makers - value of the money
2. Free market - is it dead? 
3. Traditional ways - political agenda - economic agenda? 
4. Air Canada - TSX: AC - $9 billion in liquidity, lost near $2.5 billion over 6 months alone, $10 million/ daily, but market cap remains above $5 billion
5. 
   

The market is rigged

In a recent interview with Bloomberg, Dalio outlined what he really thinks about the stock market in 2020.

“Today the economy and the markets are driven by the central banks and the coordination with the central government,” he said. “We’re in a situation now where they’re the market makers…including the value of money.”

Dalio warned that the entire concept of free markets is now dead. “Capital markets are not free markets allocating resources in the traditional ways,” he stressed. “They have a political agenda, not an economic agenda.”

It’s not hard to see how markets are overinflated. Just look at Air Canada (TSX:AC). The company has $9 billion in liquidity and lost nearly $2.5 billion over the last 180 days alone. The daily burn rate is likely above $10 million. Bankruptcy is a serious consideration, yet the market cap remains above $5 billion!

Follow Dalio’s advice

Dalio isn’t the only one concerned.

Jeremy Grantham, head of GMO Asset Management, is an expert at spotting bubbles. He foresaw the property bubble in Japan, the dot-com bubble in the 1990s, and the financial crisis of 2008. He’s often a year or two early, but investors that trusted his opinion weren’t too concerned, as they avoided losses of 50% to 90%.

What does Grantham have to say about the current environment?

“Everything is uncertain, perhaps to a unique degree,” he begins, after noting that the current economy is in the worst 10%, or even bottom 1% in history.

“The market’s P/E level typically reflects current conditions. Markets have historically loved fat margins, low inflation, stability and, by inference, low levels of uncertainty. This is apparently one of the most impressive mismatches in history,” he concludes.

Dalio and Grantham are clearly concerned about the market’s frothiness. Grantham is pointing out the historical mismatch. Dalio is placing the blame on government intervention.

AC.TO stock: Yahoo -> Finance -> Financials -> Income statement ->Quarterly

 August 19, 2020

Introduction

As an investor, I like to work on some basics. One of ideas is to watch some youtube channel, and see how others are working. I like to read more carefully about Air Canada quarterly income statement. 

Yahoo -> Finance -> Financials -> Income statement ->Quarterly

I like to find out how many shares Air Canada 

Sabr stock: Public offering

 Sabre Corporation ("Sabre") (Nasdaq: SABR) today announced registered public offerings (the "Offerings") of (1) $250,000,000 of mandatory convertible preferred stock (or $287,500,000 if the underwriters fully exercise their overallotment option to purchase additional shares) and (2) $250,000,000 of common stock (or $287,500,000 if the underwriters fully exercise their option to purchase additional shares). The precise timing, size and terms of the offerings are subject to market conditions and other factors. The net proceeds from the Offerings will be used for general corporate purposes. The completion of each Offering is not contingent on the consummation of the other Offering.

Each share of preferred stock is expected to have a liquidation preference of $100.00 per share. Unless earlier converted, each share of preferred stock will automatically convert into a variable number of shares of Sabre's common stock on the mandatory conversion date, which is expected to be September 1, 2023. The dividend rate and the conversion terms of the preferred stock will be determined by negotiations between Sabre and the underwriters.

Brex: A Business Card That Doesn’t Require a Personal Guarantee

 Here is the article. 

BUY Air Canada After Earnings? - What I'm Doing

 Here is the link. 

1.752 billion dollars loss - second quarter 2020

Unrestricted liquidity - 9,120 - keep the business afloat 

Free cash flow (1,493) - 

Net debt - 4,564 

Consumer as an example:

ALL The Stocks I Bought Recently - Portfolio Update

 Here is the link. 

Fenviz -> Screener -> Performance -> Perf YTD

 August 18, 2020

Introduction

It is important for me to explore Finviz and understand what product features can be very helpful. So I like to look into Screener -> performance -> Perf YTD. I like to find those stocks like big five store or overstock, so that I can evaluate which stocks I should invest. 

Build wealth

It takes time for me to learn more about mistakes as an investor and a beginner. I do like to explore product features on fenviz, and then I can quickly undertand those top performers. 

Hedge fund - positions second quarters

 Here is the article. 

What I like to do is to go over those stocks and then spend 10 minutes for each stock. I need to look into more business and understand how things work under this Coronavirus environment. 

Micron technology:

 Here is the link. 

Air Canada: Extended Travel Restrictions Could Tank Air Canada (TSX:AC) Stock More

 Here is the article. 

Here are highlights:

1. AC earns 22% of its passenger revenue from the U.S. transborder
2. Second quarter - reduce capacity 97.7% in the second quarter
3. Burning 20 million a day, 80% of last year profit - $3.55 billion
4. First six months of 2020 - 2.8 billion, next six months of 2020, 1.5 billion
5. In second quarter, it raises 5.5 billion in capital, thereby increasing its liquidity to $9.12 billion

Things are getting tougher for Air Canada (TSX:AC). The Canadian government extended the travel restrictions at the Canada-U.S. border by a month, till September 21. The Canada-U.S. borders have been closed for discretionary travel since March 21, resulting in six months of reduced capacity for North American airlines. The news sent AC stock down 1.35%.

AC earns 22% of its passenger revenue from the U.S. transborder. With the border closed for six months, it had to reduce the capacity of U.S. flights by 97.7% in the second quarter. It will see similar capacity reductions in the third quarter as well.

Air Canada’s mounting losses

In my previous article on AC, I was bearish on the stock, because the airline is likely to operate at just a fraction of its capacity for the entire year. The airline is burning $20 million cash every day, which has vanished almost 80% of its last three years’ combined profit of $3.55 billion. It has already lost $2.8 billion in the first six months and could lose another $1.5 billion in the next six months.

AC is doing almost everything to save cash. It has adopted a three-step approach to cut $1.3 billion in costs and delay bankruptcy:

• It has slashed 50% of its workforce in June, which would halve its second-biggest expense after fuel.
• The airline is retiring 75 aircraft, which equates to more than 30% of its overall fleet. It is also willing to cancel orders for new aircraft if needed. I believe this need will soon arise.
• It is raising cash from every possible source, such as stocks, debt, loans against aircraft, and credit facility. In the second quarter, it raised $5.5 billion in the capital, thereby increasing its liquidity to $9.12 billion.
• 
  

The rocky runway to recovery

While its three-step approach will help AC reduce its cash burn, the recovery will only begin when its planes take off from the runaway. The airline saw some demand for domestic travel and cargo. But that is not enough to begin the recovery. It needs international long-distance flights because they make most of the profits.

Any recovery in international travel will most likely begin in 2021. AC expects international travel to return to the pre-pandemic by 2023. Many analysts find three years to be an overly optimistic estimate. But even if we go by this estimate, AC will take seven to 10 years to see any profit.

BGFV stock: over 200% rebound after March 2020 crash

 RECOMMENDATION 

We rate BIG 5 SPORTING GOODS CORP (BGFV) a HOLD. The primary factors that have impacted our rating are mixed - some indicating strength, some showing weaknesses, with little evidence to justify the expectation of either a positive or negative performance for this stock relative to most other stocks. The company's strengths can be seen in multiple areas, such as its solid stock price performance, compelling growth in net income and attractive valuation levels. However, as a counter to these strengths, we also find weaknesses including generally higher debt management risk and poor profit margins. 

HIGHLIGHTS 

This stock has managed to rise its share value by 236.12% over the past twelve months. Regarding the stock's future course, our hold rating indicates that we do not recommend additional investment in this stock despite its gains in the past year. 

BIG 5 SPORTING GOODS CORP has shown improvement in its earnings for its most recently reported quarter when compared with the same quarter a year earlier. The company has demonstrated a pattern of positive earnings per share growth over the past two years. During the past fiscal year, BIG 5 SPORTING GOODS CORP turned its bottom line around by earning $0.40 versus -$0.16 in the prior year. 

Regardless of the drop in revenue, the company managed to outperform against the subsector average of 11.0%. Since the same quarter one year prior, revenues slightly dropped by 5.4%. The declining revenue has not hurt the company's bottom line, with increasing earnings per share. 

The gross profit margin for BIG 5 SPORTING GOODS CORP is currently lower than what is desirable, coming in at 33.66%. Regardless of BGFV's low profit margin, it has managed to increase from the same period last year. Despite the mixed results of the gross profit margin, the net profit margin of 4.88% trails the subsector average.

SPG stock: challenge time in coronavirus

 Giant mall owner Simon Property Group is pursuing an unorthodox business strategy, smashing the foundation of the traditional industry model on the one hand while trying to glue certain elements of it back together with the other.

Simon has been in talks with Amazon.com Inc. to convert department stores into warehouse distribution hubs, say people familiar with the matter, an innovation that could plug large holes filled by ailing tenants such as Sears Holdings Corp. and J.C. Penney Co. But the move would challenge a long-held industry belief that anchor tenants are crucial for attracting foot traffic to other stores.

At the same time, Simon has been trying to keep aspects of the old business model intact, despite heightened pressure from e-commerce and other forces that have pushed some once-prominent retailers into bankruptcy. It is using cash to help stabilize some companies whose demise would mean closing stores in Simon malls.

The mall operator and a partner recently agreed to buy apparel retailers Brooks Brothers Inc. and Lucky Brand Dungarees LLC out of chapter 11. With another partner, Simon is in advanced talks to buy J.C. Penney.

One thing the two strategies have in common: a focus on maintaining occupancy levels at Simon malls as high as possible. Analysts say there is still a glut of malls, and that as many as half of the roughly 1,100 U.S. malls could shut for good as tenants close their doors.

Some view Simon's moves as boosting the company's income while buying time to reconfigure malls with only one anchor department store.

"Nobody in the $5.5 trillion-a-year retail business stands to lose more from bankrupt tenants or declining tenants than Simon Property right now, " said Nick Egelanian, president of SiteWorks, a retail consulting firm. "They need to keep rents flowing. I see it as the natural conclusion of the 50-year run of the mall industry."

Some investors said they think Simon Property is being astute and making out-of-favor investments that might seem foolhardy now but could pay off in the long term. Shares of the largest U.S. mall owner by number of malls are flat since June 30, when news started to emerge that it was interested in buying more flagging retailers. The S&P 500 rose around 9.1% during the same period.

Air Canada promotes leisure flights despite travel advisories

 Here is the article. 

Air Canada is promoting “leisure and business” flights to the U.S. at a time when tens of thousands of Americans are getting infected by the novel coronavirus every day and as federal travel advisories continue to warn against any non-essential travel out of the country.

• U.S. airlines try to convince wary public to fly amid coronavirus uptick
• Air Canada promoting ‘leisure’ travel to U.S. despite advisories warning against non-essential trips

American Airlines warns 25,000 employees about potential job cuts as coronavirus continues to sap demand

 Here is the article. 

• U.S. airlines have urged employees to take buyouts or early retirement packages to cut costs.
• American told employees earlier this month that it expects to be overstaffed by more than 20,000 people this fall.
• Carriers are prohibited from laying off workers until Oct. 1 under the terms of $25 billion in federal payroll support.

• American Airlines on Wednesday warned about 25,000 front-line employees — roughly 29% of its U.S. mainline workforce — that they could be furloughed this fall, the latest carrier to prepare staff for job cuts as surges in coronavirus cases dash hopes for a quick rebound in travel demand.

  The airline also urged employees to take new extended leaves that can last up to two years or early retirement packages to get as many people off payroll as possible before having to involuntarily cut their jobs. 

  American’s revenue in June was down more than 80% than a year ago, CEO Doug Parker and President Robert Isom said in a note to staff.

Think like beginner: stocks sold and purchase on August 17, 2020

 August 17, 2020

Introduction

It is important for me to show something as a beginner. I like to show concerns about hotel business in USA. So I sold those profit stocks and purchase PED, PK and also SAVE stocks today. 

Stocks sold

Stocks purchased

Blue Chip Borrowers Rush to Lock In Low Rates

 Here is the link. 

New debt sales from blue-chip companies are poised to reach a record for annual issuance this week as more opportunistic borrowers lock in some of the lowest borrowing costs in history. Meanwhile, high-yield supply may slow to a trickle.

Investment-grade syndicate desks are anticipating about $30 billion in new bond sales for the week, which would push total volume for the year past the current supply record of $1.3 trillion for all of 2017. Supply could reach $1.9 trillion by the end of the year, according to Monica Erickson, head of investment-grade corporates at Doubleline Group LP.

Apple Inc. led other high-quality companies in borrowing $48.8 billion last week, easily surpassing the top projection for $35 billion. Risk premiums on U.S. investment-grade corporate bonds have tightened substantially to early March levels and yields are flirting with the lowest levels in history, according to Bloomberg Barclays index data.

Stock research: 3 Things to Watch in the Stock Market This Week

 Here is the article. 

NVIDIA's data center sales

Computing chip giant NVIDIA will announce its latest results on Wednesday afternoon, and its surging stock price year to date suggests a high bar for this report. Shares have doubled in 2020 as the fiscal second-quarter announcement approaches.

NVIDIA's previous results gave investors plenty to feel excited about. Revenue spiked 39% overall, thanks mainly to standout results from the data center segment, which crossed $1 billion in quarterly revenue for the first time. "The demand is the strongest we've ever had in data centers," CEO Jensen Huang said in the late May earnings call.

Huang's initial outlook for the fiscal second quarter called for sales to land around $3.65 billion, and we'll learn this week whether that projection was a bit too cautious. The headline grabbing update this week will likely be NVIDIA's outlook, though, which should incorporate robust demand in areas like PC and console gaming for the second half of 2020.

Mathmatician: Paul Richard Halmos，1916–2006

 Here is the article. 

我之所以成长为一名数学工作者，并热衷于几何观点下的线性代数，与一个人有很大的关系，这个人就是美国数学家哈尔莫斯（Paul Richard Halmos，1916–2006）。我第一次接触到哈尔莫斯，是通过他的数学自传《我要作数学家》[1]。不记得是大一还是大二，当时我在南开大学数学院的图书资料室闲逛，偶然看到这本书。翻开前几页，我立刻就迷上了它。哈尔莫斯写道（[1]，p. 4）：

“

我主张讲解问题要多用文字少用数字，特别是讲解数学时要这样做。在数学中，创造精妙的符号体系（以表示乘积、方幂、级数、积分等一切计算概念），常常是一大进步，然而，使用符号虽然能简化计算，同样也会导致概念变得晦涩难懂。

”

接下来哈尔莫斯举了一个例子来说明文字的优越性，他只用一句话就点透了内积空间中著名的贝塞尔（F. Bessel）不等式的证明，令我大开眼界，并永志不忘。我觉得自己学到了妙招，在此之前我从未听到有老师这样讲数学。

Prof. Lu zhiqing - 陆志勤：记交大数学系二三事

 Here is the article. 

I spent time from 1984 to 1988 in math department of SJTU as well. All those teachers are my teachers as well. 

It is so surprising to learn so many stories about those stories. 

作者 | 陆志勤

来源 | 本文原载于上海交通大学数学系组编的《数学系八十年》（上海交通大学出版社，2013年），感谢陆志勤教授授权转载并提供照片。

作者简介：陆志勤，上海交大数学系本科、硕士，柯朗研究所博士，现任教于加州大学尔湾分校数学系，研究方向为微分几何。陆志勤教授不仅研究成果丰硕，而且有许多高水平的数学普及文章和报告，见他的主页 https://www.math.uci.edu/~zlu/zhongwen-vita.html，其中Erdos-Mordell inequality and beyond从三角几何谈到了他本人的研究工作。

教我们70121班数学分析的主讲老师是顾振达老师，助教是吴忠英老师。顾老师治学严谨，对学生又和蔼可亲。按规定，我们的作业都是助教批改的，但是顾老师经常专门批改我的作业。每一次看到顾老师改过的作业本，我都十分感激，也为自己在作业中偷懒被顾老师发现而羞愧。

初学数学分析的时候，有很多的习题不会做。甚至是吉米多维奇的习题集我也做不全。同时，在1982年左右的时间里，课外参考书很少。我记得只有《吉米多维奇习题集》，克莱鲍尔的《数学分析》，以及Polya & Szego的《数学分析中的问题和定理》等寥寥几本书。1983年夏天，顾先生把他自己的书——徐利治的《数学分析的方法及例题选讲》借给了我，我如获至宝。在整个1983年暑假中，我反复学习研究徐利治书中的习题。我甚至抄录下该书中的所有习题。该抄本我珍藏至今。

1983年的秋天，我将徐利治的书还给顾老师。顾老师问我看得怎么样了。我说基本看完。顾老师问我有没有看过陶贝尔定理，我说只看了小o陶贝尔定理，Littlewood的大O陶贝尔定理太难，看不下去。结果顾老师说了下面一句话使我终生难忘：“要有恒心，慢慢看就会懂的。”我一直谨记顾老师的这句话，凡遇到困难，决不放弃。一定要到搞懂为止，不管花多少时间。

到了美国我才知道，有恒心、不放弃在美国被称为persistence。我看到的大数学家们无不有persistence的素质。哪怕只是写一篇博士论文，也必须忍受至少二、三年的挫折和孤独。如果没有恒心，可能连博士也毕不了业。

在交大本科的时候，我除了十分幸运地遇到顾老师之外，还十分幸运地遇到了陆少华老师，他教我们高等代数。

听陆老师的讲课是一种美的享受。陆老师的课立意精确，又不拘泥于繁琐。他往往能在众多表象中抽出最本质的东西。可以想象，对于一个高中刚毕业的我，陆老师的高等代数课向我展示了数学的深谨和美好。

我至今还记得陆老师给我们做的一道习题：“证明在 n 维欧几里得空间中不存在n+2个非零向量 v₁, v₂ , … , v_n+2 使得它们两两之间的夹角都是钝角”。当n=2时，该问题是显然的。但是高维的情形对一个大一的学生来讲可以说是一道难题。我做出了这个问题，直至今日，我还能记得解决该问题后的欢欣和喜悦。

和顾老师一样，陆老师对我的鼓励和鞭策也是我终身难忘的。

在交大本科的学习中，还有许多老师教过我的课。我能回忆起来的有张益杰(解析几何、机械识图)，陈大新(常微)，陆心杰(复变)，乐经良(数理方程)，概率(许重光)，统计(徐明钧)，胡鸿钊(数值分析)，谢如彪(非线性方程)，倪弘杰（矩阵计算)，屠规彰(微分几何)，何焕熹(Fortran和Unix)。

如果说顾、陆两位老师对我的本科学习帮助极大，那么陈志华先生对我的帮助、指导和提携，奠定了我在美国发展的坚实基础。

在大四下半学期的时候，我旁听了陈志华先生的“多复变函数”课，立刻被深深地吸引了。很难描述我当时的感觉，应该说我是十分shock。大四的时候，我对自己的数学能力十分自满，但陈老师的课我几乎只能听懂20%。陈老师让我看到世界上还有如此艰深、漂亮的数学。我毫不犹豫地跟了陈老师做研究生。

陈老师具有一个优秀导师所具备的一切素质。在他的指导下，我的数学水平有了飞速的提高。1986年我参加了复旦的数学暑期班，听钟家庆先生讲授“多元复分析”(助教为杨洪苍老师)。1986年的暑期班汇集了全国最好的学生78人，在最后的考试中只有两个学生得了A+，我是其中之一。能得到这样的成绩，给我以后的发展起了很大的鼓舞作用，同时也展示了上海交大的数学水平。

现举一些小事。

1. 陈先生的数学素养很高，在读研究生期间，他先教我们“多复变函数”，然后又教我们“微分几何”，并且(十分正确地)指出，结合多复变与微分几何的复几何是世界潮流。陈先生的指路，使我出国后十分容易地融入主流核心数学。

2. 第一次给陈先生痛骂，是在我第一次做学术报告的时候。我以为准备得十分充分了，结果还差得很远。那个报告讲得很糟糕。挨骂之后，我每次演讲都花很多时间准备，演讲的技术也突飞猛进。2000年，我找教职的时候，四个面试我拿下了三个 (另外一个给了我博士后工作)。

3. 陈先生从来不吝对学生经济上的资助。我1986年在复旦和1987年在长沙的暑期学校的学习，开阔了视野。有一次办公室的老师骂我们复印费用得太多，要我们“负责任”。陈先生哈哈一笑，说我们没钱，怎么负得起责任。结果陈老师用他的科研经费支付了我们所有的复印费。在八十年代，如果能有经费复印出所有的感兴趣的文章，对学生们科研的帮助是十分巨大的。

在上海交大数学系，我打下了坚实的数学基础。这使我在柯朗研究所读博士时游刃有余。我在半年内就以第一名的成绩通过了博士资格考试，并且我所有的成绩都是A。然后在田刚老师的指导下，拿下了博士学位。光阴似箭，18年过去了，当年的雄关已不复为险隘，但饮水思源，对于当年帮助我、鼓励我克服种种困难的老师们，我有一种深深的敬意和思念。

Scaling Facebook Live Videos to a Billion Users

 Here is the link. 

Network flapping

 Here is the article. 

Flapping

Written by Editor  in Letter F

Flapping, in computer networking, is a problem condition that can occur with dynamic routers on large internet works. Learn all about flapping-routers reading this article.

What is Flapping?

A problem condition that can occur with dynamic routers on large internet works. When a router is flapping (called a “flapping router”), it broadcasts routing table updates that alternate between two different routes to a host.

For example, the flapping router might indicate during the first broadcast that route A is the best route to a given host, indicate during the second broadcast that route B is the best route, indicate during the following broadcast that route A is best, and so on.

Flapping routers thus generate unnecessary routing traffic over the network. This generally happens when a router is unnecessarily configured to load-balance between paths with equal hop counts. To determine whether a router is flapping, use a network packet sniffer.

To check out best seller routers on Amazon click here.

System design: My workshops - Learn distributed system

 August 16, 2020

Introduction

It is time for me to learn system design. The way I can play a trick is to pretend that I will have an offer from Facebook, and I need to rush myself in one week to learn large distributed system. How many things can I learn and what good contents I can find and choose to learn from if I have time. 

Curiosity

It is hard for me to understand myself. I have so many ideas to work on things, but it ends up that I do not work on system design enough since my first onsite from Amazon Vancouver in June 2016. 

System design: Turning Caches into Distributed Systems with mcrouter - Data@Scale

August 16, 2020

Introduction

It is best time for me to learn system design. I do not have to worry about onsite system design, and I have time to take break, no need to run a Leetcode marathon. It is best time for me to learn something about FACEBOOK distributed system. 

Mcrouter -  

Here is the link.

2:57/ 32:04

Usage models

- demand-filled, look-aside cache

     - "standard model" of memocache

    - suggest model for most use cases

- Non-durable store

    - Your data could disappear at any moment!

- Fast published store

    - Lookup regularly published values

     - Often replicated for redundancy

Set TTL - 

6:00 - 32:04

Memcache at Facebook

- Query cache for expensive TAO/DB queries

    - Birthday index

    - Typeahead bootstrap data

- Replicated cache for extremely hot TAO/DB data

    - chat visibility

Memcache at Facebook

- write-heavy, non-durable storage

    - For data that is nice-to-have, but not necessary for correct operation

    - Might be a performance or quality optimization

- Example 

    - Complex calculation analytics

8:38/ 32:04

What we want

As simple as a single memcached instance, except:

 - server never fails

 - Network never flaps

 -It has limitless memory

 - It offers infinite read throughput

 - All clients see uniformly low latency

mcrouter 

- feels as simple as a sginle memcached instance

- operates as a robust distributed system

- 

10:16/32:04

From memcached to Memcache

Not just backspace

 - As the system scales, we encounter many issues

    - growing working set

    - high read rates

    - Heterogeneous workloads

    - hardware and transient network failures

    - Inter-cluster inconsistencies

    - Planned maintenance and data center issues

Growing working set

    - account confirmation status

Turning Caches into Distributed Systems with mcrouter - Data@Scale

 Here is the link. 

Ryan McElroy, software engineer at Facebook, introduces "mcrouter," software that the company has developed for turning standalone caches into a robust distributed system.

System Design distributed web crawler to crawl Billions of web pages | web crawler system design

 Here is the link. 

Learn webcrawler system design, software architecture Design a distributed web crawler that will crawl all the pages on the internet. Question asked in most of the top company interviews like GOOGLE, FACEBOOK, and AMAZON Let's learn how to build google sipderbot or google distributed web crawler.

Bloom filter

 Here is the article. 

A Bloom filter is a space-efficient probabilistic data structure, conceived by Burton Howard Bloom in 1970, that is used to test whether an element is a member of a set. False positive matches are possible, but false negatives are not – in other words, a query returns either "possibly in set" or "definitely not in set". Elements can be added to the set, but not removed (though this can be addressed with the counting Bloom filter variant); the more items added, the larger the probability of false positives.

Bloom proposed the technique for applications where the amount of source data would require an impractically large amount of memory if "conventional" error-free hashing techniques were applied. He gave the example of a hyphenation algorithm for a dictionary of 500,000 words, out of which 90% follow simple hyphenation rules, but the remaining 10% require expensive disk accesses to retrieve specific hyphenation patterns. With sufficient core memory, an error-free hash could be used to eliminate all unnecessary disk accesses; on the other hand, with limited core memory, Bloom's technique uses a smaller hash area but still eliminates most unnecessary accesses. For example, a hash area only 15% of the size needed by an ideal error-free hash still eliminates 85% of the disk accesses.^[1]

More generally, fewer than 10 bits per element are required for a 1% false positive probability, independent of the size or number of elements in the set.^[2]

Robots exclusion standard

 Here is the article talking about web crawl's text format file. 

System design: Build a Web Crawler

 Here is the link. 

#1 – Basic solution

How to build a rudimentary web crawler?

One simple idea we’ve talked about in 8 Things You Need to Know Before a System Design Interview is to start simple. Let’s focus on building a very rudimentary web crawler that runs on a single machine with single thread. With this simple solution, we can keep optimizing later on.

To crawler a single web page, all we need is to issue a HTTP GET request to the corresponding URL and parse the response data, which is kind of the core of a crawler. With that in mind, a basic web crawler can work like this:

• Start with a URL pool that contains all the websites we want to crawl.
• For each URL, issue a HTTP GET request to fetch the web page content.
• Parse the content (usually HTML) and extract potential URLs that we want to crawl.
• Add new URLs to the pool and keep crawling.

It depends on the specific problem, sometimes we may have a separate system that generates URLs to crawl. For instance, a program can keep listening to RSS feeds and for every new article, it can add the URL into the crawling pool.

 

Behavior interview preparation: Archive the handwriting notes

 August 15, 2020

Introduction

It is my job to make sure that I should take pictures of my behavior questions two hours preparation on Thursday morning, and I like to review them later. It is hard for me to understand where I am in my career, and one thing I can help is to document them, and review them in short future. 

Behavior questions

STAR method is most popular one. I learn better this time from those questions. 

Tech titan Barry Diller discusses the future of tech, media, and the internet economy

 Here is the link. 

Barry Diller, Chairman & Senior Executive, IAC & Expedia, sat down with CNBC Reporter Julia Boorstin to talk the future of tech, media, and net neutrality at Internet Association’s 2017 Virtuous Circle Conference.

Barry Diller: Guard against arrogance by forgetting your success

 Here is the link. 

— "I remember thinking, I see the people around me getting really arrogant. And I learned how awful a poison arrogance is. And so one of the ways you guard against arrogance is to forget success. So I just always tried to brush it clean. Sometimes successfully." — •Yahoo Finance Editor-in-Chief Andy Serwer sits down with Barry Diller, IAC chairman and senior executive. Diller offers his take on the different media mergers and the evolution of the industry, while praising Netflix. He calls for more tech regulation, but suggests that the public has overreacted over Facebook. The media mogul looks back on his time with Fox and praises Rupert Murdoch for his vision and courage. Diller slams President Donald Trump, calling his win of the 2016 election, an "accident."

What Barry Diller Knows About Travel

 Here is the link. 

WSJ's Scott McCartney joins Tanya Rivero to discuss his interview with IAC and Expedia chairman Barry Diller about where travel is headed next. Photo: Getty

Barry Diller On President Donald Trump: Hopefully Will Be Over Soon | CNBC

 Here is the link.