tricky tricky airline price

I know a little bit about revenue management, such as littlewood's rule. In my mind, the price of air ticket should stochastically increase. When I try to book the tickets to Orlando from the southwest during the winter break, the price change of air ticket is quite dymatically as I can imagine. The lowest one way price in my case is $59. This price will be randomly available at each day. Moreover, the number of available seats also change at each day. That might be due to change of reservation by the other people. But it may not be entirely true.

Yesterday when other couple reserved one ticket at one time slot(depart at 12:00) and tried to reserved anther one at the same time slot, it failed since there was only one slot remaining before they reserved. So they changed to 10:00 now. Today that slot is available too. It seems that someone change or cancell their reservation yesterday. But it is not just that. I changed mine 12:55 to 10:00 in order we can go togather. But I cannot find available seats for 12:55 today(Yesterday 12:55 is unavailable). One possible explanation is that demand at 12:55 is stochastically higher than demand at 10:00 with respect to the same price. So southwest move the tickets available from me to higher price. But I don't think this is the whole story. What is the control mechnism of air ticket price at southwest is still a puzzle to me.

Btw: southwest allows you to change your reservation without any penalty. That is why "Last August, low-cost king Southwest Airlines carried more passengers than any other U.S. airline, the first time an LCC has claimed the top spot." reported by Time

Stochastic processes@wikipedia

I haven't seen most of them. A long way to go!

Poster presentation next year at INFORMS charpter@Lehigh?

Today Lehigh's INFORMS chapter had its first meeting this semester. Basically we discuss who will be invited as INFORMS chapter seminar speaker next semester. After that, we need to figure out a way to spend increased budget. There is one idea comes out during the discussion. That is we will provide T-shirt having ISE logo. I like this idea a lot. At least we need something to connecting people togather.

Right after meeting, I get an idea about create poster presentation next year. Now in our department, those optimization people have very strong connection. They have their own CORAL and IP seminar. But the connection outside optimization is quite loose. So hope this poster presentation will let people know what the other people do. And every poster presenter should wear the ISE T-shirt.

I also get idea to create subdivision leader in our chapter, say, optimization, stochastic, finance, scm&rm. Each leader should arrange 3 weeks long seminar. This is just coming from IP seminar yesterday.

Maybe we can also create the connection between IE and other department student, so that we can see what cool stuff we can do for other fields.

And just now, I send an email to our president about giving a talk to the first year phd student of the career path of phd. It is very often to mention in the company but seldom done by university. I guess after that we can also create Q&A page for all IE student.

I believe by doing more stuff like that. We can create the best INFORMS charpter ever and sell OR to more people.

If we can get enough people joining us, we can also make the newsletter once a semester. Maybe some short introduction about what happens to every member in our chapter. What had done last semester and what we will do next sememster.

Keeping your direction, don't just follow fashion

This Friday, Kevin Shang gave us a talk about multi-echolen inventory problem. It is very classical problem but there aren't many people focusing on this area. And the barrier to this area is higher than most other areas related to inventory theory. So most people like to chase research 'fashion'. Somebody told me that a few years ago, sessions of SCM are full of people. But in this Informs meetings, RM seems more popular. A lot of people talk about dynamic pricing etc.

But Shang sticks to multi-echolen inventory problem after he passed his qualify exam. And he told me that he will continue to explore this area. It should be appreciate. Although our field just like a branch of applied math, it doesn't mean that everybody should just apply similar math technics to different applications. Once the math is too hard to go on in one area, then everybody shift their research interests. I don't mean that we shouldn't do so. In contrast, we need some people to do so to spread out our field. But what I mean is that we need some people to develop some unique math methods to solve those unsolved problems. Like developing in physics can push math forward. Why won't our IE people do the similar things? (Btw: I am not talking about those optimization people in IE fields)

Actually, I am a guy, who cannot focus on one thing for a long time. I like to find tons of applications, which can be easy in math. But I will find an area which can attract me for at least ten years. Of course, I will do other things on the same time.

What should I do in the next Informs meeting?

• Since I already get to know some friends from this conference, I hope I can meet each one individually and have deep conversation. Also because, I will have more time to do research from the fourth year, I hope to seek more opportunities to work on the different subjects with different people with their own expertise
• Prepare some deeper work to present. That's the only way to impress people, so that they are willing to work with you if possible.
• Get to know job market
• Create the chance to talk with those faculties
• Last but the most important, live at a hotel nearby the convention center. I run into trafic every day and get too less sleep every day during conference. And I haven't recovered yet.

internal force(nei gong) or external technic(zhao shu)?

I went to an Informs conference from Nov. 4 to Nov. 8. Everything goes well. Meeting and making friends is the most important thing for me since our department only has very few people sharing the same interests with me. I need to extend my network. Second thing is to present my work. It is ok since nobody left during my talk and I got two questions and handled well in my opinion.

But there is one fundamental question occuring several times during the conference. On one hand, we need to have good papers before we graduate. It means that I need to work hard on generating papers, which implies that I need to read a lot of literature. As Long told me that we need to accumulate several tricks which are used by different authors again and again in their papers but no one collect and publish those as a reference book. This is absolutely right. Even those great mathematicians has only a few tricks. On the other hand, I like to take as much courses as I can since I believe only when you have complete skill set, you can consider problems from different angles which gives you more insight. Also you can do something crossing the different fields.

In Chinese Wuxia novel, there are two kind of persons. One is working on internal force(nei gong) . It takes a long time to master. The other person is working on external technic(zhao shu). It is fast to learn but easy to hit the bottleneck. In the short run, the people working on zhao shu can easily beat the previous type of people since the stuff they learn is more practical. But in the long run, the previous people can outperform the people only having zhao shu since it has more power.

In this conference, when people start to talk about those 'famous' people's name, I feel a little bit embarrassing since I cannot recognize a lot of those 'big' names. I start to think whether I spend too much time in taking course other than reading related literature. For example, the next semester, I plan to take two courses and audit another two courses again. But I stick to finish those courses since I won't get any time to do so after I graduate. And only when you have enough nei gong, you can pick up those tricks quickly. I am not worried about my ability to come up ideas. Actually, during this Informs, I generate several new ideas. For now, I need to focus on developing those nei gong and try to work on only one or two ideas. After next semester, I would devote most of time into research but not now.

MSOM 2006 submission statistics

Till the latest data, there are 154 submission for the regular issues and 36 submission for the special issue.

For the regular issues, there only 4 papers(2.6%) get accepted. Among these 4, there are 2 papers get accepted without going through review process. 8 papers(5.19%) get minor revision and 35 papers(22.73%) get major revision.

For the special issue, 4 papers(11%) get major revision and 4 papers have got the decision. All other paper got rejected.

You can access data from http://msom.pubs.informs.org/msomdata.xls

The accpetion ratio is very low. MSOM currently publishs 4 issues a year. And each issue contain around 6 papers. So the acception ratio is around 24/(154+36)=12%. That means around 2/3 major revision paper will get rejected finally.

Lehigh ranked 18th undergraduate B-school

It is a little bit surprising to see Lehigh can get 18th rank in that category. ANyway, it is still a good news.

Beamer's columns

\frame
{
\frametitle{Interview}

\begin{columns}
\begin{column}{0.5\textwidth}
\begin{itemize}
\item current symptoms
\item past medical history
\item family history
\item social history
\item review of systems
\end{itemize}
\end{column}

\begin{column}{0.5\textwidth}
\begin{itemize}
\item detect hypertension
\item recognize emergency
\item recognize reversible causes
\item find chronic target organ damage
\item discover co-morbid conditions
\item plan therapy
\end{itemize}
\end{column}
\end{columns}
}

You can have as many columns, of whatever widths, as you like. Note that
within a column, \textwidth will correspond to the column width, not the
width of the beamer slide, so it works pretty much like minipage.
Material within columns is vertically centred, and you can have part of
the slide in normal (single column) format, and other parts in more than
one column.

Insert List into Tabular in Latex

Here is the code. But I still cannot figure out how to do under Beamer. The ultimate goal is to insert the Figure into the left top corner and put the list on the right.

\documentclass[12pt]{article}
\makeatletter % Yes, it's horrible
\def\spacehack{%
\@minipagetrue% % Disables spacing above
\expandafter\everypar\expandafter{% % Add stuff to \everypar
\the\everypar% % Do what was there before
\@minipagefalse% % Clear the mystic flag
\everypar={}% % And reset \everypar
}%
\let\@oldbs=\\% % Remember old \\ command
\def\\{\nointerlineskip\@oldbs}% % Turn off final odd spacing
}
\makeatother

%
\begin{document}
%
\begin{tabular}{p{40mm}p{40mm}p{40mm}}\hline
& Advantages & Disadvantages \\ \hline
Method 1 & \spacehack\begin{enumerate}
\setlength{\itemsep}{-\parsep}
\item item one
\item item two
\item item three
\end{enumerate} & \spacehack\begin{enumerate}
\item item one
\item item two
\end{enumerate} \\[-12pt] \hline
Method 2 & \begin{enumerate}
\item item one
\end{enumerate} & \begin{enumerate}
\item item one
\item item two
\end{enumerate} \\ \hline
Method 3 & \begin{enumerate}
\item item one
\end{enumerate} & \begin{enumerate}
\item item one
\end{enumerate} \\ \hline
\end{tabular}

\end{document}

How to be a good lecturer?

You need

• Have interesting problem (not to be too hard and too specific, especially when your audience background is mixed
• Always talking something that is easy to understand.
• More figures than words and formula
• I will add more here

How to be a good listener?

From those experience, I see there are several keys to be a good listener.

• Try to understand the main point
• Try to answers all the questions other people ask
• Try to think all possible ways to attack their theory
• A good lecturer is neccessary

How I remember those speakers' presentation(2004, Fall)?

Yesterday I read through the advice to the young scientist. It gives some advice about how to do a good talk. The first advice is 'Every lecture should make only one main point. ' And the fouth advice is 'Give them something to take home.'. What can make people remember you. Here is the answer.

It is not easy to follow this advice. It is easier to state what features of a
lecture the audience will always remember, and the answer is not pretty.
I
often meet, in airports, in the street, and occasionally in embarrassing
situations, MIT alumni who have taken one or more courses from me. Most of the
time they admit that they have forgotten the subject of the course and all the
mathematics I thought I had taught them. However, they will gladly recall some
joke, some anecdote, some quirk, some side remark, or some mistake I made.

So I want to recall all the seminar in our department I attend to see what I remember from those talks. Then I may know how to improve my presentation. And how to be a good audience. Here I need to clarify. The talks I don't remember now may be due to that I don't have enough knowledge at that time. I begin from 2004, Fall which is my first semester here.

2004 Fall, I attended all the seminars. The following is the talks that I still have an impression.

08/27/04 David Drake Lehigh Phd student: This is first seminar I attended. The only thing I still can remember is that he thought HongKang is nice place.

9/17/04 Suvrajeet Sen. Program director at NSF. This was the time that every professor was going to take notes. I remember that Dr. Ralphs and Linderoth asked some questions about software patent.

11/5/04 Aurelie Thiele. Lehigh. I know newsboby model can also extend to revenue management. But the terminology is different. Basically, for the simple concave problem, the optimal solution is achieved at marginal cost equal to marginal revenue. In the revenue management, if we have high fare class and low fare class. The number of seats reserved to high fare class is achieved at expected revenue brought by high fair class is equal to expected revenue brought by low fare class.

12/3/04 Krishnan Anand, Upenn, There was an interesting situation that sometimes information may cause increase of inventory. I also remember there is an question related to Wal-mart. Later on, I find a good explanation and email it to Prof. Anand.

An example of converge in probability but not almost sure converge

This is one homework question in stochastic process class. I cannot come up even one example by myself. First I use goole, nothing valuable is found. Then I http://books.google.com/. I get a book named 'Counterexamples in Probability and Statistics'. The example is X_n=H_n, where H_n is Bernoulli variable with probability 1/n to be 1. X_n converge to 1 in probability. But Prob(H_n = 1 infinity often)=1 by Borel Cantelli Lemma.

2 hours to clearn up the inbox

I store all the emails in the box and only delete some when I get the warning about storage. Last time I did clearning is last semester. Today I spent 2 hours to move every email to the proper local folders. It is a good chance to see what I have done since the end of last semester. Although the outcome of research isn't that breakthrough, I am still satisfied with how I deal with those multi-tasks. Now I have fewer things to do. I can put more emphasis on each thing I am doing.

Advice for the Young Scientist

Another related article mentioned is Ten Lessons I Wish I Had Been Taught

My presentation@IP seminar: "rondom thoughts about optimization"

Yesterday I did my first outside class presentation Since my research is not mainly about optimization, I have to make up some stuff to fit the audience's interest. Also I hope that my talk can create some coordination between students in our department. So I just provide several of my ideas which I think that might be attractive to other people.

The result of presentation is OK, at least people don't feel bored during that 50 min. But I am sure that I don't achieve my target fully, since no one shows strong interests. Larry told me that my confidence overcomes my spoken English. Prof. Huang shows a different approach to solve one of my problems about LP and regression after presentation, where there is no need to change matrix A but only constants on RHS. Also I find another way too. We can just change one column instead of replacing the rows. Prof. Linderoth also provides me how do sampling in multi-stage stochastic programming. Prof. Ralphs reminds me how to get dual solution easily. Ash shows interest on my network formulation and I explain to him about bootstrap idea further. Zumbul told me that she has her own problem and want to coordinate with me. Finally my wife told me that I put too much contact with those professors and lose contact to the students.

Finally, I should say I need focus. After that I hope get any coordination with other students.

I have three SCM books now

After struggling for a while, I final decided to buy two more SCM books. They are

• The logic of logistics
• Foundations of stochastics inventory theory

Plus I already have

• Foundations of Inventory Management

Also I copy

• Inventory Control

What else do I need to collect?

The best deal for the Economist ever

Today when I got books from Amazon. I found such good coupon. There is only $100 for 51 issues of Economist plus $25 Amazon coupon. I wish that I could have to read.

Prediction of Nobel Prize in Economics 2006

I guess it would belong to Bhagwati, Dixit and Krugman since their topic is more interesting to me.