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Java Forum / First Aid / December 2005need help on this problem.
Hello, I have an assignment for school. I'm looking for help and advise on how to solve this. My professor is bad, meaning that she can't explain correctly, her english is bad, and it's one of those people that expect students to know everything. well, this is the problem: On a floor, parallel lines separated of a length L are drawn. When you launch a pen of length L on this floor, the probability that it crosses a line is 2/Pi. Suppose that you have a computer that has 64 processors. Write a program to compute Pi in java for that computer. But run it on your computer. I went to her to explain me certain things I didn't understand. For example, the lines are drawn parallel like this: | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | and L is the distance between each line. The pen's width (not the length like she wrote it) is L as well. For the rest, the pen is thrown at random. So for example, the pen can fall diagonally or vertically or horizontally. Does anyone else understand this problem? I don't, that's why I'm asking for help from anyone that might have a clue. Even after I visited her her explainations are bad and don't help at all. I was hoping that someone can help me guess what I need to do, since I have no clue. I already spent 2 days on this and I can't come up with anything. I appreciate anyone reading this. Thanks. p.s. and please, i'm not looking for solutions, so please don't start b.s.ing or bashing the post. > On a floor, parallel lines separated of a length L are drawn. When > you launch a pen of length L on this floor, the probability that it > crosses a line is 2/Pi. I believe that this problem is known as "Buffon's Needle", and that you will find lots of information and analysis if you search using that name. For example: http://www.mste.uiuc.edu/reese/buffon/buffon.html /gordon  Signature[ do not email me copies of your followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > Hello, > [quoted text clipped - 38 lines] > p.s. and please, i'm not looking for solutions, so please don't start > b.s.ing or bashing the post. I'd say you're in a very awkward position. I truly don't understand what your prof wants from this description but that's not surprising since you obviously don't either. I'm particularly baffled by how pens thrown over lines on the floor have anything to do with calculating pi on a computer with 64 processors. Perhaps she is using some kind of metaphor to illustrate the algorithm you'll need but it isn't one I've ever seen before. The main issue seems to that she isn't able to state the problem clearly due to difficulties with English. It simply isn't fair of her to expect you to solve the problem if she can't explain it clearly. I'm tempted to question the wisdom of hiring someone to teach when they can't speak the student's language clearly but I remember my own university days when profs who were not terribly fluent at English were not unusual. A variety of possible strategies come to mind: 1. Go to her again and make her explain the problem again. Explain to her very politely that you are having trouble understanding her due to her accent but that you really want to understand. See if she can go over it all again, as slowly and carefully as possible. Ask her to draw diagrams or do real life simulations of the problem so that you can understand what she wants. (For example, put some actual lines on the floor and throw pens over them and get her to explain how this gives the value of pi.) If this doesn't clarify things, see if either you or she can find a third party to translate. Maybe one of your fellow students or another prof is fluent in her language and can get it explained in the prof's native language, then translate it for you. 2. Consult with your fellow students and see if any of them understand what is required. If any of them expresses very high confidence that they understand the problem, get them to explain it to you. (It might be a good idea to then go to the prof to verify that this is the correct explanation of the problem. Your confident friend may simply be mistaken.) 3. If the first two strategies don't pay off and everyone is just as confused as ever, you should probably go to the prof and say that you and everyone else in the class are completely baffled. It might be helpful to bring a cross-section of the class with you so that she understands it is not just you who are struggling. Ask her if she can give a different problem that is more comprehensible. Make it very clear that you are not trying to defy her or get an easier assignment and that you are willing to tackle the original problem if she can possibly clarify it. 4. If you still can't get anywhere, see her supervisor - the department head? - and explain the problem to the supervisor. Again, make it clear that you genuinely want to do the assignment, you just don't understand what it is. In my opinion, the key here is to give everyone involved, especially the prof, the benefit of the doubt. She's probably very smart and is probably doing her best to give you a challenging assignment that will teach you a lot about programming. She's probably as frustrated by her deficiencies in English as you are. She may also have overestimated the backgrounds of her students and may need a bit of a reality check. If she is new to your country and not familiar with the educational system there, she may think students have more experience than you actually do. We all make bad assumptions sometimes and she may have done that in this case. Rhino Hi, > Hello, > > I have an assignment for school. I'm looking for help and advise on how > to solve this. My professor is bad, meaning that she > can't explain correctly, her english is bad, and it's one of those > people that expect students to know everything. First of all: Is your professor from Germany? (I'm asking because I think I understand the question, and my English is not so good (because I'm from Germany) ;-) Anyhow: > well, this is the problem: > > On a floor, parallel lines separated of a length L are drawn. When you > launch a pen of length L on this floor, the probability that it crosses > a line is 2/Pi. OK, that is not so complicated, I think: You drop the pen several times (lets say N times). In some cases, the pen will cross a line, in other cases it will not. Lets say, it crosses the line in n cases. Now, the theory says that the probability that the pen crosses the line is: n/N=2/Pi <=> Pi=2*N/n So, by throwing the pen a lot of times, you are able to approximate Pi. > Suppose that you have a computer that has 64 > processors. Write a program to compute Pi in java for that computer. > But run it on your computer. OK, now you can throw the pen yourself, or you can write a simulation that simulates how a pen is thrown. There is a x-coord and an angle a which are randomly distributed. From x and a you can calculate if the pen crosses one of the lines (*). By repeating this N times, you can approximate Pi. (*) I suppose, for calculating this simulation, you need Pi! ;-) Ciao, Ingo Hey Ingo and the rest, I like the help you three have provided. Rhino: I WILL go to her tomorrow and ask one more time. I'll also ask my colleagues as well. Some seem to have solved it already. I just wanted to do this on my own this time. Gordon Beaton: Thanks for the info. I have seen before that these professors sometimes copy material off another university or website and give it to us as an assignment. Some assignments are nice and it's cool that they got it for us from other sources, but some are just crap. It seems that they might not want to put too much effort in their assignments. I'll look into your link right away. It would be interesting to find out where this problem came from. Ingo: You are close! She is Dutch. I'm actually going to a University in The Netherlands. www.fdaw.unimaas.nl I have had similar situations on how I don't understand their English at all because of how they use it, but my girlfriend does, since she is Dutch as well. I think what you provided is close to what I might need to do, so I'll look into it. At least what you stated is close to what she was trying to tell me. Thanks again guys. > Hey Ingo and the rest, > [quoted text clipped - 3 lines] > my colleagues as well. Some seem to have solved it already. I just > wanted to do this on my own this time. I'm not saying you should ask your colleagues for the _solution_, just for a clarification of the _question_. You'll learn a lot more if you try to solve the problem alone than if you just imitate someone else's solution. :-) > Gordon Beaton: Thanks for the info. I have seen before that these > professors sometimes copy material off another university or website [quoted text clipped - 10 lines] > you provided is close to what I might need to do, so I'll look into it. > At least what you stated is close to what she was trying to tell me. Oh, that's a surprise: YOU are the foreigner, not the professor! I thought the prof was the foreigner. Hmm, that makes things harder for you since you are the foreigner and there is less pressure for them to accomodate you than if your prof was the foreigner and you were the native speaker. Well, it could have been much worse :-) The English spoken by the Dutch is a lot closer to Anglo-American English than you will hear in some other countries! I imagine you'll be developing a lot of insights into the subtleties between different dialects of English as you live in a place that has English as a second language, rather than a first one..... Good luck with your assignment and your studies in the Netherlands! Rhino > > Suppose that you have a computer that has 64 >> processors. Write a program to compute Pi in java for that computer. [quoted text clipped - 6 lines] > > (*) I suppose, for calculating this simulation, you need Pi! ;-) This last point is the part that confused me the most. I assumed that you had to simulate throwing the pen, but for this simulation you need Pi, but since you're trying to compute pi, presumably you don't know Pi yet! It did not occur to me that perhaps the assignment was to throw the pen in real life, and then write a computer program that kept track of how many line-crosses you got, and approximate Pi that way. I'm also not sure where the "64 processors" part comes into play, unless this is actually an assignment on parallel programming. - Oliver Hi, >>(*) I suppose, for calculating this simulation, you need Pi! ;-) > > This last point is the part that confused me the most. I assumed that > you had to simulate throwing the pen, but for this simulation you need Pi, > but since you're trying to compute pi, presumably you don't know Pi yet! Yes, the question is: Is this a trick of the prof. or didn't she realise that, or does she think it is OK to use Pi to calculate Pi :-) *Perhaps* (I'm not sure and I'm not a mathematican) it is possible to simulate the problem with a very rough approximation of Pi (say '1' ;-) and to get a better approximation of Pi by this (perhaps '3'). Then, run a new set of simulations to approximate it further. Perhaps that is a bad idea, perhaps it is possible. I just don't know, but I would consider thinking about that. > It did not occur to me that perhaps the assignment was to throw the pen > in real life, and then write a computer program that kept track of how many > line-crosses you got, and approximate Pi that way. For this, you do not need a computer program - a simple pocket calculator (or even a piece of papaer an d a pen ;-) is enough! :-) > I'm also not sure where the "64 processors" part comes into play, unless > this is actually an assignment on parallel programming. Hm, you can simulate it in 64 different threads and mediate the result, which improves the precision you are able to calculate in a constant amount of time. Ciao, Ingo Hi, >>> (*) I suppose, for calculating this simulation, you need Pi! ;-) Thinking more about it, that's not really true: You just need cos and sin which you can approximate with a weighted sum (somehting like a^2/2!+a^4/4!+a^6/6!+...). You do not need Pi directly (although everything concerning this depends on each other and you can approximate Pi with a similar sum, iirc) Ciao, Ingo > Hi, > [quoted text clipped - 42 lines] > Ciao, > Ingo I'm glad I checked back on this thread :-) I was really wondering how dropping a pen could help you compute pi and you've explained it very well, Ingo! Now the problem starts to make sense to me.... Rhino Hey Rhino :), Interestingly enough, you make some interesting remarks. First off, by me saying that I would check with my colleagues didn't mean that I was going to copy or base my answer from them. I would "check" what they understood from the problem just like I'm dong by posting this message. Another thing, yes, I'm the foreigner. However, I'm from the U.S. and I know what I'm saying when I talk. It's funny because the professors sometimes don't know what to say and they look at me and ask "how do you say that?", and then I pronounce the word. it happens from things like how to say ';' (semicolon) to something like comparable. So I think that I'm not the one with the problem, but they have the problem. Specially since they started offering the english program to attract more foreign students. I think that they should be more careful with their english because other students might learn their errors and speak like them. but anyway, that's something else. i just wanted to add that small bit. But even with those remarks, I have to say that the Dutch speak a pretty good English. It's just sometimes with technical stuff (like in this case) that words get difficult. > Hey Rhino :), > > Interestingly enough, you make some interesting remarks. First off, by > me saying that I would check with my colleagues didn't mean that I was > going to copy or base my answer from them. I would "check" what they > understood from the problem just like I'm dong by posting this message. I wasn't accusing you of anything negative :-) You said something about wanting to do the assignments alone for a change, or words to that effect, and it brought back memories of doing assignments in some courses with my fellow students. In my case, this was something of a crutch although it certainly helped me get through the assignments more quickly. However, I later did the assignments on my own: it took me longer but I definitely learned more so it was better for me to do it that way. It struck me that you might mean that you were trying the same thing so I was just trying to be supportive and encourage you to do the assignments alone. > Another thing, yes, I'm the foreigner. However, I'm from the U.S. and I > know what I'm saying when I talk. It's funny because the professors [quoted text clipped - 7 lines] > like them. but anyway, that's something else. i just wanted to add that > small bit. Yes, I see. It's an interesting situation! They're teaching you but learning from you at the same time. You're obviously a better authority on English since you're a native speaker but you're still a student who is there primarily to learn things that your profs are expert at. I can relate to the situation a bit. I'm Canadian and living in the English-speaking portion of the country. I've had French courses and did okay with them - in a classroom - but when I travel to Quebec, it's a lot like travelling in a foreign country even though I haven't crossed a national border. In the French-speaking parts of Quebec, which is most of the province, I'm like a foreigner. When French-speakers speak English to me, I'm conscious of their accents and the occasional grammar or pronunciation mistake but I feel sure that my French is far worse than their English. I envy them their relative fluency in my language and regret my own relative weakness in their language. > But even with those remarks, I have to say that the Dutch speak a > pretty good English. It's just sometimes with technical stuff (like in > this case) that words get difficult. I know what you mean. I was in the Netherlands in 1983 as a tourist and was very pleasantly surprised by how the younger people all seemed to speak fluent English. I was quite surprised by how good their English was, considering that they learned it as a second language - or in some cases, as a third or fourth or fifth language! (I talked to a Swiss guy on a computer forum a few times and was amazed by how good his English was. I asked if he had an English speaking parent or had been educated in English; he just laughed and said English was his fourth language. They'd had a little bit of English in school but he mostly learned the language from rock videos, which were invariably in English!) I hope you take a few moments now and again to reflect on how lucky you are to have such an experience; aside from the stresses of trying to understand assignments by profs who speak English imperfectly, it should be very good for you :-) Rhino Hi, I must agree to Rhino here, I think you are in a situation which could be much worse: I remember my time at the university were the prof came from asia and had to talk english with germans and some russians - no one was a native speaker and our dialects were not only bad but even worse they differed! > But even with those remarks, I have to say that the Dutch speak a > pretty good English. It's just sometimes with technical stuff (like in > this case) that words get difficult. Interesting: I think, my technical English is OK, but when I try to do some small talk in English, I'm facing problems. Even watching DVDs in original language (=English) is very difficult for me since it has beeen common in Germany for eons of years that all movies were translated and (before DVDs) it was in fact extremely difficult to see a move in a language other than german (quite different to some northern Europe countries, where it was common to see the movies in English with native subtitles). Ciao, Ingo > Hi, > [quoted text clipped - 3 lines] > native speaker and our dialects were not only bad but even worse they > differed! Oh dear! I'll bet that was very difficult! Still, it would have been _much_ harder if you had _no_ languages in common :-) >> But even with those remarks, I have to say that the Dutch speak a >> pretty good English. It's just sometimes with technical stuff (like in >> this case) that words get difficult. > > Interesting: I think, my technical English is OK, but when I try to do > some small talk in English, I'm facing problems. Really? It's the opposite for me! I have some French and German and I can probably manage to converse on general topics easily enough - What's for dinner? Where is the WC? etc. - but don't have any technical vocabulary to speak of. (I know that 'computer' is 'ordinateur' in French and I think it is 'Rechner' in German but after that I'm lost.) I've worked with internationalization and localization in my applications a bit and had to post to newsgroups to find out what terms a German or French person would typically use for words like "Exit" or "Save". But I've also had fairly lengthy conversations in German on trains about general topics like the German reunification. Mind you, I know what you're saying. I went camping with a Vietnamese friend a few years ago. She and her husband, who was also born and raised in Vietnam, were camping with several of their Vietnamese relatives and I dropped by for the afternoon to visit with them. Lien's sister, who has lived in France since the late 1970s was one of the relatives; she was there with her husband and kids. Lien's sister spoke a very good English so we agreed that she would speak to me in English, to help her improve it, and I would speak to her in French, to improve my French. It was very easy for me to follow her English and I asked her how she'd learned the language, since English is not widely spoken in France. It turns out that she was a CICS system programmer and all the manuals for CICS were in English so she'd had to learn English, mostly from the manuals, in order to do her job! I still find that amazing; I can't imagine learning German (or Vietnamese) from a computer manual written in that language! The odd thing is that Lien's sister and I were _not_ discussing computers when we talked; I asked where they lived, how they liked living in France, how old the children were, etc., nothing remotely computer-related. She had obviously expanded her knowledge of English well beyond what she needed to read her CICS manuals. > Even watching DVDs in original language (=English) is very difficult for > me since it has beeen common in Germany for eons of years that all movies > were translated and (before DVDs) it was in fact extremely difficult to > see a move in a language other than german (quite different to some > northern Europe countries, where it was common to see the movies in > English with native subtitles). It's the same for me! I've tried to watch German TV programs in German and find I quickly get quite lost, unless it is something for very young children. I didn't have much trouble following the Teletubbies in German but a game show or movie was more difficult. I think the only real antidote is full immersion in the other language for several months or years. Then, things should be a lot easier. Tchuss, Rhino On Fri, 9 Dec 2005 09:43:05 -0500, "Rhino" <no.offline.contact.please@nospam.com> wrote, quoted or indirectly quoted someone who said : >find out what terms a German or French person would >typically use for words like "Exit" or "Save". You can't solve that with a dictionary. You have to learn the conventions by looking at other French software. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > On Fri, 9 Dec 2005 09:43:05 -0500, "Rhino" > <no.offline.contact.please@nospam.com> wrote, quoted or indirectly [quoted text clipped - 5 lines] > You can't solve that with a dictionary. You have to learn the > conventions by looking at other French software. Or ask native German- or French-speakers who used computers, which I did by using German and French newsgroups. That was easier than trying to acquire and use existing programs written in German and French. Rhino On Fri, 9 Dec 2005 18:13:43 -0500, "Rhino" <no.offline.contact.please@nospam.com> wrote, quoted or indirectly quoted someone who said : >> You can't solve that with a dictionary. You have to learn the >> conventions by looking at other French software. > >Or ask native German- or French-speakers who used computers, which I did by >using German and French newsgroups. That was easier than trying to acquire >and use existing programs written in German and French. If anyone knows of word lists for the conventional words used for various computer related equipment buttons and menuitems, in various languages, I will compile them in a table in the java glossary under internationalisation. I have prepared such as list for Esperanto at http://mindprod.com/esperanto/esperanto.html Perhaps we could start by getting the list for English and various language speakers could help fill in the gaps. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Java custom programming, consulting and coaching. > If anyone knows of word lists for the conventional words used for > various computer related equipment buttons and menuitems, in various [quoted text clipped - 6 lines] > Perhaps we could start by getting the list for English and various > language speakers could help fill in the gaps. One hurdle is that such terms are not nescessarily standardized. Even in English, some applications call it "&Quit", and others call it "E&xit". There might also be subtle differences that sometimes matter and sometimes don't. E.g. I expect "quit" to always mean "quit the entire application", but I can imagine "exit" might mean "exit this submodule to return to the main module of the application". Here, the difference matters, but in the case of "File -> Quit" versus "File -> Exit", the different doesn't matter. Translation tends to be a tricky thing to get perfect. - Oliver > If anyone knows of word lists for the conventional words used for > various computer related equipment buttons and menuitems, in various > languages, I will compile them in a table in the java glossary under > internationalisation. Sun already compiled such a list. It is part of the Java GUI style guide. IMHO such lists are of no great help when localizing an application. You get what you pay for, and paying a professional translator and native speaker specialized in localizing software is probably your best bet. Otherwise you get the GUI equivalent of these dreaded instructions which have been "translated" from Chinese to English to German or whatever. /Thomas SignatureThe comp.lang.java.gui FAQ: ftp://ftp.cs.uu.nl/pub/NEWS.ANSWERS/computer-lang/java/gui/faq http://www.uni-giessen.de/faq/archiv/computer-lang.java.gui.faq/ Hi, >>find out what terms a German or French person would >>typically use for words like "Exit" or "Save". > > You can't solve that with a dictionary. You have to learn the > conventions by looking at other French software. In Germany, the advantage is that the "international" words "computer" or "save" are more common than the German translations "Rechner" and "speichern". I think there is no German who does *not* know these words (perhaps because of the fact that much software is not localized, but in English). So, technical English is quite easy for Germans. Ciao, Ingo > Hello, > [quoted text clipped - 10 lines] > processors. Write a program to compute Pi in java for that computer. > But run it on your computer. This is known as a Monte Carlo Method. Buffon's Needle to be precise. If you search the web for Buffon's Needle you will find more detail on how you can approximate PI using this method. The history behind this is that the lines are cracks in the floor boards and the pen was actually needles. Buffon, in 1733, dropped needles on the floor and calculate how often the needles crossed the spaces between floor boards. The correct formula is, if given a needle of length L and lines evenly spaced by a distance of D then the probability of the needle overlapping a line is: 2*L / PI*D If we set L = 1 and D = 1 (inch, centimetre, etc. does not matter) then we get the: 2 / PI > I went to her to explain me certain things I didn't understand. For > example, the lines are drawn parallel like this: [quoted text clipped - 10 lines] > at random. So for example, the pen can fall diagonally or vertically or > horizontally. She is correct that it is the pen's LENGTH not the width that needs to be measured. > Does anyone else understand this problem? I don't, that's why I'm asking > for help from anyone that might have a clue. Even after I visited her > her explainations are bad and don't help at all. I was hoping that > someone can help me guess what I need to do, since I have no clue. I > already spent 2 days on this and I can't come up with anything. I > appreciate anyone reading this. You need to: - Create a class called Line - Create instance of Line that represent the lines on the floor - Using Random, create random instances of Line - Create a method that determines if two Line intersect SignatureSend e-mail to: darrell dot grainger at utoronto dot ca > You need to: > > - Create a class called Line > - Create instance of Line that represent the lines on the floor > - Using Random, create random instances of Line At this step, you cannot just use a uniform distribution for endpoints of the lines that represent the needles to be thrown, right? Otherwise the lines might not end up being the correct length. The technique I'm thinking is to use a fixed length line and then apply a random amount of rotation on it, and then placing it at a random position, but the random rotation bit assumes you already have a value for Pi. > - Create a method that determines if two Line intersect - Oliver I'm studying what "." wrote, and I can't quite grasp the idea of creating random instances of Line. How can you do that? I also started thinking like Oliver, which is the first step to take? What exactly should be randomized? Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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