Robust scheduling

This has been puzzling me recently: When we are making schedules, for simplicity we mostly assume that there is no uncertainty involved. Now, I don't want to imply that no research has been done, the Pinedo's book contains several chapters;  but in real-world applications, everything seems to be deterministic.
Of course sometimes you don't mind - when scheduling school classes, you can be pretty sure that a good deterministic schedule will work fine. On the other hand, sometimes ignoring uncertainty is just impossible and this has been recognized - in airline operations for instance, disruptions occur all the time.

In manufacturing, the situation seems as bleak as in aviation industry, even though manifestations of uncertainty may be less spectacular and perhaps because of this, the uncertainty aspect is less stressed. In my current manufacturing OR adventure, I have encountered in principle two related views on uncertainty:

1. Handling disruption is what manufacturing managers are for. Scheduling tools can help (among other things) to make sure that day-to-day planning and scheduling is done appropriately when nothing weird happens.
2. The factory should have certain amount of well-managed buffers (e.g. overtime possibilities, surplus stocks) which can help them get back to normal when an unexpected event occurs.

 Now from a view of "advanced planning & scheduling champion", it is hard to passively accept such views. I want to plan in a way which at least implicitly reflects my recognition of uncertainty - this can mean making schedules insensitive to small changes ("robust scheduling"). Ideally one could, based on the past data, say which parts of the schedule touch volatile resources and hence need more insensitivity and which parts can be assumed rather stable.
As for the buffers, a question is how to put the phrase "well-managed" in more concrete terms. Given my amount of such and such uncertainty, what is my "optimal" amount of such and such buffers?

Now this is an area I want to learn about, so I can't flood you with a discussion of existing approaches... Still, I know there is this "robust scheduling" stuff. Incorporating uncertainty directly, e.g. by taking processing times to be random variables, seems just too complex to swallow, at least for systems with more than 2 machines...Still, under the label of Stochastic optimization one can find, among other approaches, simulation of possible scenarios - a schedule is made for each - and from these what-if schedules, a final schedule can be obtained by taking kind-of-expected-value. The idea of running a scheduling algorithm  for each scenario seems off-putting from the computer-time perspective; still, the concept seems attractive.
Well, enough said for today...

Farewell, Netherlands

Time to leave. Still, the two years have given me so much - unforgettable memory and a whole new direction in my life and... a lot of amazement from a new culture.
Bikes - everywhere; the most confident and prominent part of the traffic. And be careful when you come here - it's just too easy to get rid over by a bicycle! To make it even worse, the state of some bikes is desolate - in other lands, such bikes would not be allowed to enter a city (indeed, for instance, the Netherlands is unique in that it doesn't require bikes to have a hand brake - apparently there is no expectation that cyclists would need to brake...)
Water - everywhere. On the one hand, you have the omnipresent canals and ditches. And the fact that some parts of the Netherlands have been under the sea a few years ago... On the other hand, it's raining all the time and Dutch people talk incessantly about the weather.
The cohesive society - I was just amazed by the number of association (verenigingen) - student associations, sport association, cultural associations, you name it... The Netherlands has one of the largest percentages of volunteers in the population among European countries and "cooperative mindset" is all pervasive.
Coming from the "poor" Czech Republic, I have also noticed that "consumerism" - in a broad sense - is far more advanced in the Netherlands. People in general expect much more from their life. Almost everyone wants to own a house. Even students feel that they are entitled to live a comfortable life - so even though everyone gets a grant and a free travel card from the government, many students end up heavily indebted after their studies. A lot of people pride themselves as "environmentally conscious", but don't mind throwing away food rests or buying a new cell phone every year.
Architecture - very courageous. The first time that I went to Amsterdam and left the train in the Bijlmer Arena station, I felt as emerging in a crazy futuristic city. The UFO that I saw there just emphasized this feeling.
The Dutch are world famous for their directness or even rudeness, what a stereotype, isn't it? Still, I have noticed that the use of "please" is essentially obsolete in the Dutch language. Also, trying to use the polite form of "you" ("U") leads people quickly to shaking their heads in disbelief - even professors are addressed informally. That said, I have found the overall openness quite refreshing - there are very few tabus, people don't mind talking about sexuality, drugs, money...
Optimism - Enormous atmosphere of "we can do it" and "everything is possible". Everything should be "top" and people seek out "challenge" ("uitdaging") in what they do - at least they claim so. When you write a motivation letter for a job, it is expected that you are very very self-confident...a Czech recruiter would laugh seeing such a letter. And this optimism is also somewhat connected to the "nation of traders" tradition - many people know three foreign languages and when talking to my classmates, I sometimes have a feeling that almost everyone was an exchange student at a different continent - perhaps unsurprisingly, given that e.g. Universiteit Utrecht has exchange agreements with schools on all continents (OK, leave Antarctica out...).
Food - A shock was eating bread as lunch... Other than that, there is just overabundance of fried food - well, I guess you take the kilos down quickly when you are biking all the time... Also, when Dutch people are asked to cook a typical Dutch meal, they come up with something Surinamese or Indonesian - perhaps no one is proud of stampot or erwtensoep...

Fietsen

I've already gotten used to that Dutch people make phone calls while riding a bike (no hands-free...). But just recently, I've also seen a biker reading a book!

Gourmet's thoughts

I like broccoli with peanut butter. Matej also recommended me carrots with peanut butter. And apples with ham.

Another impressions from the Netherlands

• What makes me happy: I got a second-hand chair, second-hand table, second-hand table lamp and a mattress from IKEA... Ja, en ik al weet, hoe werkt de IKEA systeem. A few days after buying the chair, I saw a few nice chairs being dumped into a garbage in front of the Mathematics building...too late.
  

• To be a little bit cynic: first impressions from the Netherlands = bikes + rain.
• I was said that perhaps around 20-25 percent are accepted for the Mathematical Sciences...wow, I was maybe more lucky than I thought...
• How to get a job as a pure mathematician: "Go to your future employee, give them your CV. Now, what do they see? They see that you're a genius, so they're going to accept you." :-D
• Summerschool is fun, I like learning again. I like the lecturers, maybe I'm going to take their subjects in the regular school year.
• I met two of my new classmates (in the summerschool) - one from Norway, the second one from here (with Chinese parents, but apparently as Dutch as any other Dutch person). Yeah, I like them :-)
  

First impressions from Netherlands

Not all of the impressions, just what has come to my mind just now.
I arrived on Friday with Wizz Air to Eindhoven. Cheap flight - pretty comfortable actually, people complain because of too little leg space, my legs are short enough, no problems with them :-)
Plenty of brick houses - just the whole city made of brick houses. Also seen a mosque there; a lot of Muslim people there. It caught my attention, but then why not, it may well have been an organic part of the city.
Arrived to Utrecht, by train. Train was very cheap, though pretty comfortable, a little bit airplane-like. The house, where I have my room in Zeist, is just lovely; my room is bigger than I had expected. My flat mate seems like a very nice guy.
Arrived to the summer school housing - a student housing; I guess getting the room was a good choice (albeit a very lucky one). Summer school participants are all around the world - probably much more multicultural, than the people in the 3 workcamps, where I had participated.
Utrecht - a lot of bikes, a very smart city; my house in Zeist is probably closer to Uithof then a big part of the Utrecht proper.
Went to "Utrechtse Bazaar" - it was like a Moroccan suq (also, a lot of sellers were probably of Moroccan origin, I even heard some Arabic being spoken). It was huge - I have a new backpack, cost me 6e; is bigger and seems more durable than my old one (I am already thinking about the possible use of the old one...). I also visited the Vredenburg market; it had a different flavor, was also pretty big.
Second hand shopping exists, but seems not to be too widespread :-( I found an address of a few second-hands (I need a table and a chair...); have yet to visit them. The new stuff is probably too cheap.
Food - a lot of food that I like is pretty cheap (even cheaper than in the CZ); yet fruit and vegetables are expensive (not so much in the suq...but it's pretty far :-( ). There is a lot of stuff to be put on a bread, much more than just cheese, butter, jam, ham. Dutch people seem really crazy in this (for instance, chocolate flakes, used in the Czech Republic just to decorate cakes...).
In Netherlands, everything seems so neat (at least on the first sight). It seemed to me the same in other "Western" European countries; perhaps neat in different way, but always neat (of course, some cities or city quarters were exceptional, but in general it held). Perhaps this is the origin of the sentiment that we are rich enough and that we should concentrate on other stuff than getting richer; this perspective is obviously much stronger in such neat countries (but actually, the Czech Republic has been becoming more and more neater during my life as well...).
The preserved patches of nature in Eindhoven and Utrecht seemed really well preserved - water birds, rabbits (on just very small areas, where there were no buildings!!!).
Dutch people speak Dutch too quickly...; but actually, it happened to me just twice or so, that they would switch to English, seeing I was a foreigner - a nice surprise :-)
I have a new (Dutch) cell phone number.

Fortran

So I ended up working (kind of) in FZU again, this time even doing something with Math, I am just lucky being given the possibility - already now, after the first year of the university! I just hope I don't get fired too early.
But this is not, what I wanted to write about. As the work I do has something to do with computational physics, I've had to learn a suitable programming language.
So far, I have put my hands more seriously on PHP (this was because of webdesign) and, of course Pascal (and I don't count Karel far back in the early secondary school :D. Still PHP is mostly - well, just for the webdesign - and Pascal, let's face it, have always been designed to teach students basics of programming. Oh, yes, and I remember some of those basic steps in Delphi and Java.. (Delphi again because of FZU - back then; Java because I wanted to see, what Meldath was creating in it all the time.)
First, I was hoping to have to learn C; still, not truly surprisingly in an institute of physics, I was told to learn Fortran. I've always been told it's a crazy language for crazy physicists. Well, it's definitely apparent, what is the purpose of the language, and intended audience. On the other hand, (to my surprise), there have apparently been quite some changes recently (no infamous FORTRAN 77 anymore). I actually came to acknowledge, something is really joy to program in it. E.g. it was really painful to do some more serious (from the viewpoint of a first-grader, of course) programming in the ancient Turbo Pascal. Yet in some of this stuff actually lies the Fortran's main power (I always thought Fortran was used just because of the vast number of libraries available - not true).
Let's see - the support for complex arithmetic is built inside by default. There is a pretty convenient system of handling "modules" (that means - user-built libraries). What I really love - the possibility to name every control structure in the code - and compiler will nicely localize errors for you this way. Possibility to handle new data types and defining arbitrary operators on them really easily. Lots of built-in mathematical functions - and easy-to-use libraries to provide another ones. No I don't say this is not possible to use these functions in other languages, just so far, the Fortran's way to do this is somehow most readily available. I just now don't like the idea of having to write the program in Pascal in order to get my Programming credit ;)

Let fly a dragonfly!

Ever roving near a river or a pond, watching a dragonfly staying at one place, and then, suddenly, popping up just nearby? Actually, the dragonfly is not staying at one place. It's moving toward you, yet in the way, that you perceive it stationary.

Even when moving, most animals
have a good sense of the direction to a given fixed object at any time,
and expect to see it on that line. If the aggressor moves so that at each
moment it is on the line between the target and a given fixed point,
which could be its initial position, then its relative motion in the eyes
of the target is the same as that of the stationary reference point. The
only way that the target can know that it is not stationary is to notice the change in size of the aggressor as it approaches.

Look here to read a more understandable (i. e. with a picture) description.
Fascinating :-)

Biodiesel at home

Vera sent me an interesting link concerning how to make biodiesel at home from cooking oil. I suggest that you take it with a grain of salt, yet it's interesting (and also amusing). Just don't get poisoned ;-)

Comparison of Livejournal and Blogger

Recently, I moved my blog from Livejournal to Blogger. I maybe wanted to distract myself a bit, I thought Blogger had some interesting features and I also liked Google.
For now, I'm quite content with my blog at Blogger (except for that I haven't had much time to post recently), though in some things Livejournal may have been better.

• Livejournal was much more profiled toward diaries; there was the "memories" feature, user groups, "friends" and stuff like that; one can mostly emulate it in Blogger as well, though.
• With Livejournal, I had feeling that there were almost no new features added. And those added were mostly designed only to suscribers - that irritated me greatly; on the other hand Blogger has no subscribing and money is raised by other means.
• Contrastingly, in Blogger (and other Google products as well), there are new features being added constantly. Not that I would need it, but I like experimenting.
• There is more that you can do with your blog in Blogger - one can customize it freely; on the other hand, in Livejournal there were many more (and prettier) templates.
• Blogger is a little bit buggy, seems to me; but I may reasonably expect bugs to be fixed quickly.
• The overall design of Livejournal looked better.
• Blogger account may be the same as Google account.
  

An important advantage of the Bohr's model

http://www.ped.muni.cz/wphy/FyzVla/index.htm :

The Bohr model is the last model which could be understood using "common sense". Yet shortly after its creation, it was criticized on various grounds (...) Therefore the last model was created - the quantum-mechanical one (unfortunately, a clear imagination of this model is impossible).