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• Code Golf: Leibniz formula for Pi

  - by Greg Beech

  I recently posted one of my favourite interview whiteboard coding questions in "What's your more controversial programming opinion", which is to write a function that computes Pi using the Leibniz formula. It can be approached in a number of different ways, and the exit condition takes a bit of thought, so I thought it might make an interesting code golf question. Shortest code wins! Given that Pi can be estimated using the function 4 * (1 - 1/3 + 1/5 - 1/7 + ...) with more terms giving greater accuracy, write a function that calculates Pi to within 0.00001. Edit: 3 Jan 2008 As suggested in the comments I changed the exit condition to be within 0.00001 as that's what I really meant (an accuracy 5 decimal places is much harder due to rounding and so I wouldn't want to ask that in an interview, whereas within 0.00001 is an easier to understand and implement exit condition). Also, to answer the comments, I guess my intention was that the solution should compute the number of iterations, or check when it had done enough, but there's nothing to prevent you from pre-computing the number of iterations and using that number. I really asked the question out of interest to see what people would come up with.

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• Navigating through a sea of hype

  - by wouldLikeACrystalBall

  This is a vague, open question, so if you have no interest in these, please leave now. A few years ago it seemed everyone thought the death of desktop software was imminent. Web applications were the future. Everyone would move to cloud-based software-as-a-service systems, and developing applications for specific end-user platforms like Windows would soon become something of a ghetto. Joel's "How Microsoft Lost the API War" was but one of many such pieces sounding the death knell for this way of software development. Flash-forward to 2010, and the hype is all around mobile devices, particularly the iPhone. Software-as-a-Service vendors--even small ones such as YCombinator startups--go out of their way to build custom applications for the iPhone and other smart phone devices; applications that can be quite sophisticated, that run only on specific hardware and software architectures and are thus inherently incompatible. Now some of you are probably thinking, "Well, only the decline of desktop software was predicted; mobile devices aren't desktops." But the term was used by those predicting its demise to mean laptops also, and really any platform capable of running a browser. What was promised was a world where HTML and related standards would supplant native applications and their inherent difficulties. We would all code to the browser, not the OS. But here we are in 2010 with the AppStore bulging and development for the iPad just revving up. A few days ago, I saw someone on Hacker News claim that the future of computing was entirely in small, portable devices. Apparently the future is underpowered, requires dexterous thumbs and induces near-sightedness. How do those who so vehemently asserted one thing now assert the opposite with equal vehemence, without making even the slightest admission of error? And further, how are we as developers supposed to sift through all of this? I bought into the whole web-standards utopianism that was in vogue back in '06-'07 and now feel like it was a mistake. Is there some formula one can apply rather than a mere appeal to experience?

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• MacPorts - Installing Port, Dependencies Failed

  - by Louis

  I am attempting to install xulrunner on OSX 10.6.3 using the following: sudo port install xulrunner However, I am receiving the following error: nat-10-200-136-126:phoneyc-new $ sudo port install xulrunner ---> Computing dependencies for xulrunner ---> Activating zlib @1.2.5_0 Error: The following dependencies failed to build: gconf dbus-glib glib2 zlib gtk-doc docbook-xml docbook-xml-4.1.2 xmlcatmgr docbook-xml-4.2 docbook-xml-4.3 docbook-xml-4.4 docbook-xml-4.5 docbook-xml-5.0 docbook-xsl gnome-doc-utils iso-codes libxslt libxml2 p5-xml-parser py26-libxml2 python26 bzip2 db46 gdbm openssl readline sqlite3 tk Xft2 fontconfig freetype xrender xorg-libX11 xorg-bigreqsproto xorg-inputproto xorg-kbproto xorg-libXau xorg-xproto xorg-libXdmcp xorg-util-macros xorg-xcmiscproto xorg-xextproto xorg-xf86bigfontproto xorg-xtrans xorg-renderproto tcl xorg-libXScrnSaver xorg-libXext xorg-scrnsaverproto rarian getopt intltool gnome-common p5-getopt-long p5-pathtools p5-scalar-list-utils gtk2 atk cairo libpixman libpng jasper jpeg pango shared-mime-info tiff xorg-libXcomposite xorg-compositeproto xorg-libXfixes xorg-fixesproto xorg-libXcursor xorg-libXdamage xorg-damageproto xorg-libXi xorg-libXinerama xorg-xineramaproto xorg-libXrandr xorg-randrproto orbit2 libidl policykit heimdal lcms libcanberra gstreamer bison flex gzip texinfo lzmautils libvorbis libogg libnotify nss xorg-libXt xorg-libsm xorg-libice Error: Status 1 encountered during processing. Before reporting a bug, first run the command again with the -d flag to get complete output. nat-10-200-136-126:phoneyc-new$ I am unsure how to correct this issue, so any help would be much appreciated!

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• Excel export displaying '#####...'

  - by Cypher

  I'm trying to export an Excel database into .txt (Tab Delimited), but some of my cells are quite large. When I export into a txt some of the cells are exported as '#######....' which is surprisingly useless. Has this happened to anyone else? Do you know an easy fix? Data from one cell of my column: Accounting, African Studies, Agricultural/Bioresource Engineering, Agricultural Economics, Agricultural Science, Anatomy/Cell Biology, Animal Biology, Animal Science, Anthropology, Applied Zoology, Architecture, Art History, Atmospheric/Oceanic Science, Biochemistry, Biology, Botanical Sciences, Canadian Studies, Chemical Engineering, Chemistry/Bio-Organic/Environmental/Materials,ChurchMusicPerformance, Civil Engineering/Applied Mechanics, Classics, Composition, Computer Engineering,ComputerScience, ContemporaryGerman Studies, Dietetics, Early Music Performance, Earth/Planetary Sciences, East Asian Studies, Economics, Electrical Engineering, English Literature/ Drama/Theatre/Cultural Studies, Entrepreneurship, Environment, Environmental Biology, Finance, Food Science, Foundations of Computing, French Language/Linguistics/Literature/Translation, Geography, Geography/ Urban Systems, German, German Language/Literature/Culture, Hispanic Languages/Literature/Culture,History,Humanistic Studies, Industrial Relations, Information Systems, International Business, International Development Studies, Italian Studies/Medieval/Renaissance, Jazz Performance, Jewish Studies, Keyboard Studies, Kindergarten/Elementary Education, Kindergarten/Elementary Education/Jewish Studies,Kinesiology, Labor/Management Relations, Latin American/Caribbean Studies, Linguistics, Literature/Translation, Management Science, Marketing, Materials Engineering,Mathematics,Mathematics/Statistics,Mechanical Engineering, Microbiology, Microbiology/Immunology, Middle Eastern Studies, Mining Engineering, Music, Music Education, MusicHistory,Music Technology,Music Theory,North American Studies, Nutrition,OperationsManagement,OrganizationalBehavior/Human Resources Management, Performing Arts, Philosophy, Physical Education, Physics, Physiology, Plant Sciences, Political Science, Psychology, Quebec Studies, Religious Studies/Scriptures/Interpretations/World Religions,ResourceConservation,Russian, Science for Teachers,Secondary Education, Secondary Education/Music, Secondary Education/Science, SocialWork, Sociology, Software Engineering, Soil Science, Strategic Management, Teaching of French/English as a Second Language, Theology, Wildlife Biology, Wildlife Resources, Women’s Studies.

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• Resources related to data-mining and gaming on social networks

  - by darren

  Hi all I'm interested in the problem of patterning mining among players of social networking games. For example detecting cheaters of a game, given a company's user database. So far I have been following the usual recipe for a data mining project: construct a data warehouse that aggregates significant information select a classifier, and train it with a subsectio of records from the warehouse validate classifier with another test set lather, rinse, repeat Surprisingly, I've found very little in this area regarding literature, best practices, etc. I am hoping to crowdsource the information gathering problem here. Specifically what I'm looking for: What classifiers have worked will for this type of pattern mining (it seems highly temporal, users playing games, users receiving rewards, users transferring prizes etc). Are there any highly agreed upon attributes specific to social networking / gaming data? What is a practical amount of information that should be considered? One problem I've run into is data overload, where queries and data cleansing may take days to complete. Related to point above, what hardware resources are required to produce results? I've found it difficult to estimate the amount of computing power I will require for production use. It has become apparent that a white box in the corner does not have enough horse-power for such a project. Are companies generally resorting to cloud solutions? Are they buying clusters? Basically, any resources (theoretical, academic, or practical) about implementing a social networking / gaming pattern-mining program would be very much appreciated. Thanks.

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• Computed width with decimal values in Firefox, but without decimals in Webkit

  - by jävi

  Hello one more time! I have a strange problem working with HTML,CSS in different browsers: Firefox 3.6 and Webkit browsers (Chrome & Safari). My HTML looks like this: <div class="ln-letters"> <a href="#" class="all">ALL</a> <a href="#" class="a">A</a> <a href="#" class="b">B</a> <a href="#" class="c">C</a> </div> And my CSS is... .ln-letters a { font-family: 'Lucida Grande'; font-size:14px; display:block; float:left; padding:0px 7px; border-left:1px solid silver; border-right:none; text-decoration:none; } So as you can guess, each anchor gets a different width depending on its inner text. For example the first element with the text 'ALL' will be bigger (more width) than the others. Now the problem is that in Firefox (using Firebug) I can see that the computed width for the first element is 26.5667px, while in Chrome (using Chrome's developer tools) the computed width for the same element is exactly 27px. Therefore the div.ln-letters ends with different widths in each browser and that is causing me some troubles. Question is: there is any workaround to avoid Firefox computing decimal values? Or the opposite: to force Chrome to compute decimal values? Thank you in advance!

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• Silverlight combobox performance issue

  - by Vinzz

  Hi, I'm facing a performance issue with a crowded combobox (5000 items). Rendering of the drop down list is really slow (as if it was computing all items before showing any). Do you have any trick to make this dropdown display lazy? Xaml code: <Grid x:Name="LayoutRoot"> <StackPanel Orientation="Horizontal" Width="200" Height="20"> <TextBlock>Test Combo </TextBlock> <ComboBox x:Name="fooCombo" Margin="5,0,0,0"></ComboBox> </StackPanel> </Grid> code behind: public MainPage() { InitializeComponent(); List<string> li = new List<string>(); int Max = 5000; for (int i = 0; i < Max; ++i) li.Add("Item - " + i); fooCombo.ItemsSource = li; }

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• Displaying shifts on a timetable/calendar using C#

  - by Dave Peters

  I am very much a beginner and have experience of SQL and a tiny amount of VBA. What I am looking to do is create a tool to pull shift times from a database and to display them on a timetable/calendar. It will be part of a desktop application that the (very tech illiterate) end users will use to view and amend shift patterns. In essence it will be a grid with days on one axis and people on the other (I would however like to have the blocks proportional to shift length). In my mind it would potentially be a simple Gantt chart. All computing stuff I’ve learnt has been through trial and error and I want to use this project to get a much better understanding of C# as well as to get to the end product. I have been reading around for ways to tackle the problem and my issue is creating the timetable framework to which I will bind the data. I am using Visual Studio 2010 and SQL Server 2008 R2. Do you know of good resources which will either start me on the road to designing my own interface or give a basic framework I can adapt? All the resources I’ve found so far have been in different languages or for web based applications. Thank you for your time.

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• Required Working Precision for the BBP Algorithm?

  - by brainfsck

  Hello, I'm looking to compute the nth digit of Pi in a low-memory environment. As I don't have decimals available to me, this integer-only BBP algorithm in Python has been a great starting point. I only need to calculate one digit of Pi at a time. How can I determine the lowest I can set D, the "number of digits of working precision"? D=4 gives me many correct digits, but a few digits will be off by one. For example, computing digit 393 with precision of 4 gives me 0xafda, from which I extract the digit 0xa. However, the correct digit is 0xb. No matter how high I set D, it seems that testing a sufficient number of digits finds an one where the formula returns an incorrect value. I've tried upping the precision when the digit is "close" to another, e.g. 0x3fff or 0x1000, but cannot find any good definition of "close"; for instance, calculating at digit 9798 gives me 0xcde6 , which is not very close to 0xd000, but the correct digit is 0xd. Can anyone help me figure out how much working precision is needed to calculate a given digit using this algorithm? Thank you,

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• Function approximation with Maclaurin series

  - by marines

  I need to approx (1-x)^0.25 with given accuracy (0.0001 e.g.). I'm using expansion found on Wikipedia for (1+x)^0.25. I need to stop approximating when current expression is less than the accuracy. long double s(long double x, long double d) { long double w = 1; long double n = 1; // nth expression in series long double tmp = 1; // sum while last expression is greater than accuracy while (fabsl(tmp) >= d) { tmp *= (1.25 / n - 1) * (-x); // the next expression w += tmp; // is added to approximation n++; } return w; } Don't mind long double n. :P This works well when I'm not checking value of current expression but when I'm computing 1000 or more expressions. Domain of the function is <-1;1 and s() calculates approximation well for x in <-1;~0.6. The bigger the argument is the bigger is the error of calculation. From 0.6 it exceeds the accuracy. I'm not sure if the problem is clear enough because I don't know English math language well. The thing is what's the matter with while condition and why the function s() doesn't approximate correctly.

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• OleDbExeption Was unhandled in VB.Net

  - by ritch

  Syntax error (missing operator) in query expression '((ProductID = ?) AND ((? = 1 AND Product Name IS NULL) OR (Product Name = ?)) AND ((? = 1 AND Price IS NULL) OR (Price = ?)) AND ((? = 1 AND Quantity IS NULL) OR (Quantity = ?)))'. I need some help sorting this error out in Visual Basics.Net 2008. I am trying to update records in a MS Access Database 2008. I have it being able to update one table but the other table is just not having it. Private Sub Admin_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 'Reads Users into the program from the text file (Located at Module.VB) ReadUsers() 'Connect To Access 2007 Database File con.ConnectionString = ("Provider=Microsoft.ACE.OLEDB.12.0;" & "Data Source=E:\Computing\Projects\Login\Login\bds.accdb;") con.Open() 'SQL connect 1 sql = "Select * From Clients" da = New OleDb.OleDbDataAdapter(sql, con) da.Fill(ds, "Clients") MaxRows = ds.Tables("Clients").Rows.Count intCounter = -1 'SQL connect 2 sql2 = "Select * From Products" da2 = New OleDb.OleDbDataAdapter(sql2, con) da2.Fill(ds, "Products") MaxRows2 = ds.Tables("Products").Rows.Count intCounter2 = -1 'Show Clients From Database in a ComboBox ComboBoxClients.DisplayMember = "ClientName" ComboBoxClients.ValueMember = "ClientID" ComboBoxClients.DataSource = ds.Tables("Clients") End Sub The button, the error appears on da2.update(ds, "Products") Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click Dim cb2 As New OleDb.OleDbCommandBuilder(da2) ds.Tables("Products").Rows(intCounter2).Item("Price") = ProductPriceBox.Text da2.Update(ds, "Products") 'Alerts the user that the Database has been updated MsgBox("Database Updated") End Sub However the code works on updating another table Private Sub UpdateButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles UpdateButton.Click 'Allows users to update records in the Database Dim cb As New OleDb.OleDbCommandBuilder(da) 'Changes the database contents with the content in the text fields ds.Tables("Clients").Rows(intCounter).Item("ClientName") = ClientNameBox.Text ds.Tables("Clients").Rows(intCounter).Item("ClientID") = ClientIDBox.Text ds.Tables("Clients").Rows(intCounter).Item("ClientAddress") = ClientAddressBox.Text ds.Tables("Clients").Rows(intCounter).Item("ClientTelephoneNumber") = ClientNumberBox.Text 'Updates the table withing the Database da.Update(ds, "Clients") 'Alerts the user that the Database has been updated MsgBox("Database Updated") End Sub

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• how to better (inambiguaously) use the terms CAPTCHA and various types of interactions?

  - by vgv8

  I am working on survey of state-of-the-art and trends of spam prevention techniques. I observe that non-intrusive, transparent to visitor spam prevention techniques (like context-based filtering or honey traps) are frequently called non-captcha. Is it correct understanding of term CAPTCHA which is "type of challenge-response [ 2 ]test used in computing to ensure that the response is not generated by a compute" [ 1 ] and challenge-response does not seem to imply obligatory human involvement. So, which understanding (definition) of term and classification I'd better to stick with? How would I better call CAPTCHA without direct human interaction in order to avoid ambiguity and confusion of terms understnding? How would I better (succinctly and unambiguously) coin the term for captchas requiring human interaction but without typing into textbox? How would I better (succinctly and unambiguously) coin the terms to mark the difference between human interaction with images (playing, drag&dropping, rearranging, clicking with images) vs. just recognizing them (and then typing into a textbox the answer without interaction with images)? PS. The problem is that recognition of a wiggled word in an image or typing the answer to question is also interaction and when I start to use the terms "interaction", "interactive", "captcha", "protection", "non-captcha", "non-interactive", "static", "dynamic", "visible", "hidden" the terms overlap ambiguously with which another (especailly because the definitions or their actual practice of usage are vague or contradictive). [ 1 ] http://en.wikipedia.org/wiki/CAPTCHA

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• Linux 2.6.31 Scheduler and Multithreaded Jobs

  - by dsimcha

  I run massively parallel scientific computing jobs on a shared Linux computer with 24 cores. Most of the time my jobs are capable of scaling to 24 cores when nothing else is running on this computer. However, it seems like when even one single-threaded job that isn't mine is running, my 24-thread jobs (which I set for high nice values) only manage to get ~1800% CPU (using Linux notation). Meanwhile, about 500% of the CPU cycles (again, using Linux notation) are idle. Can anyone explain this behavior and what I can do about it to get all of the 23 cores that aren't being used by someone else? Notes: In case it's relevant, I have observed this on slightly different kernel versions, though I can't remember which off the top of my head. The CPU architecture is x64. Is it at all possible that the fact that my 24-core jobs are 32-bit and the other jobs I'm competing w/ are 64-bit is relevant? Edit: One thing I just noticed is that going up to 30 threads seems to alleviate the problem to some degree. It gets me up to ~2100% CPU.

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• Where to find algorithms for standard math functions?

  - by dsimcha

  I'm looking to submit a patch to the D programming language standard library that will allow much of std.math to be evaluated at compile time using the compile-time function evaluation facilities of the language. Compile-time function evaluation has several limitations, the most important ones being: You can't use assembly language. You can't call C code or code for which the source is otherwise unavailable. Several std.math functions violate these and compile-time versions need to be written. Where can I get information on good algorithms for computing things such as logarithms, exponents, powers, and trig functions? I prefer just high level descriptions of algorithms to actual code, for two reasons: To avoid legal ambiguity and the need to make my code look "different enough" from the source to make sure I own the copyright. I want simple, portable algorithms. I don't care about micro-optimization as long as they're at least asymptotically efficient. Edit: D's compile time function evaluation model allows floating point results computed at compile time to differ from those computed at runtime anyhow, so I don't care if my compile-time algorithms don't give exactly the same result as the runtime version as long as they aren't less accurate to a practically significant extent.

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• Detecting death of spawned process using Window CRT

  - by Michael Tiller

  Executive summary: I need a way to determine whether a Windows process I've spawned via _spawnl and am communicating with using FDs from _pipe has died. Details: I'm using the low-level CRT function in Windows (_eof, _read) to communicate with a process that was spawned via a call to _spawnl (with the P_NOWAIT) flag. I'm using _pipe to create file descriptors to communicate with this spawned process and passing those descriptors (the FD #) to it on the command line. It is worth mentioning that I don't control the spawned process. It's a black box to me. It turns out that the process we are spawning occasionally crashes. I'm trying to make my code robust to this by detecting the crash. Unfortunately, I can't see a way to do this. It seems reasonable to me to expect that a call to _eof or _read on one of those descriptors would return an error status (-1) if the process had died. Unfortunately, that isn't the case. It appears that the descriptors have a life of their own independent of the spawned process. So even though the process on the other end is dead, I get no error status on the file descriptor I'm using to communicate with it. I've got the PID for the nested process (returned from the _spanwnl call) but I don't see anything I can do with that. My code works really well except for one thing. I can't detect whether the spawned process is simply busy computing me an answer or has died. If I can use the information from _pipe and _spawnl to determine if the spawned process is dead, I'll be golden. Suggestions very welcome. Thanks in advance. UPDATE: I found a fairly simple solution and added it as the selected answer.

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• Testing a wide variety of computers with a small company

  - by Tom the Junglist

  Hello everyone, I work for a small dotcom which will soon be launching a reasonably-complicated Windows program. We have uncovered a number of "WTF?" type scenarios that have turned up as the program has been passed around to the various not-technical-types that we've been unable to replicate. One of the biggest problems we're facing is that of testing: there are a total of three programmers -- only one working on this particular project, me -- no testers, and a handful of assorted other staff (sales, etc). We are also geographically isolated. The "testing lab" consists of a handful of VMWare and VPC images running sort-of fresh installs of Windows XP and Vista, which runs on my personal computer. The non-technical types try to be helpful when problems arise, we have trained them on how to most effectively report problems, and the software itself sports a wide array of diagnostic features, but since they aren't computer nerds like us their reporting is only so useful, and arranging remote control sessions to dig into the guts of their computers is time-consuming. I am looking for resources that allow us to amplify our testing abilities without having to put together an actual lab and hire beta testers. My boss mentioned rental VPS services and asked me to look in to them, however they are still largely very much self-service and I was wondering if there were any better ways. How have you, or any other companies in a similar situation handled this sort of thing? EDIT: According to the lingo, our goal here is to expand our systems testing capacity via an elastic computing platform such as Amazon EC2. At this point I am not sure suggestions of beefing up our unit/integration testing are going to help very much as we are consistently hitting walls at the systems testing phase. Has anyone attempted to do this kind of software testing on a cloud-type service like EC2? Tom

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• randomized quicksort: probability of two elements comparison?

  - by bantu

  I am reading "Probability and Computing" by M.Mitzenmacher, E.Upfal and I have problems understanding how the probability of comparison of two elements is calculated. Input: the list (y1,y2,...,YN) of numbers. We are looking for pivot element. Question: what is probability that two elements yi and yj (ji) will be compared? Answer (from book): yi and yj will be compared if either yi or yj will be selected as pivot in first draw from sequence (yi,yi+1,...,yj-1,yj). So the probablity is: 2/(y-i+1). The problem for me is initial claim: for example, picking up yi in the first draw from the whole list will cause the comparison with yj (and vice-versa) and the probability is 2/n. So, rather the "reverse" claim is true -- none of the (yi+1,...,yj-1) elements can be selected beforeyi or yj, but the "pool" size is not fixed (in first draw it is n for sure, but on the second it is smaller). Could someone please explain this, how the authors come up with such simplified conclusion? Thank you in advance

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• What are practical guidelines for evaluating a language's "Turing Completeness"?

  - by AShelly

  I've read "what-is-turing-complete" and the wikipedia page, but I'm less interested in a formal proof than in the practical implications of being Turing Complete. What I'm actually trying to decide is if the toy language I've just designed could be used as a general-purpose language. I know I can prove it is if I can write a Turing machine with it. But I don't want to go through that exercise until I'm fairly certain of success. Is there a minimum set of features without which Turing Completeness is impossible? Is there a set of features which virtually guarantees completeness? (My guess is that conditional branching and a readable/writeable memory store will get me most of the way there) EDIT: I think I've gone off on a tangent by saying "Turing Complete". I'm trying to guess with reasonable confidence that a newly invented language with a certain feature set (or alternately, a VM with a certain instruction set) would be able to compute anything worth computing. I know proving you can building a Turing machine with it is one way, but not the only way. What I was hoping for was a set of guidelines like: "if it can do X,Y,and Z, it can probably do anything".

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• Performance of Java matrix math libraries?

  - by dfrankow

  We are computing something whose runtime is bound by matrix operations. (Some details below if interested.) This experience prompted the following question: Do folk have experience with the performance of Java libraries for matrix math (e.g., multiply, inverse, etc.)? For example: JAMA: http://math.nist.gov/javanumerics/jama/ COLT: http://acs.lbl.gov/~hoschek/colt/ Apache commons math: http://commons.apache.org/math/ I searched and found nothing. Details of our speed comparison: We are using Intel FORTRAN (ifort (IFORT) 10.1 20070913). We have reimplemented it in Java (1.6) using Apache commons math 1.2 matrix ops, and it agrees to all of its digits of accuracy. (We have reasons for wanting it in Java.) (Java doubles, Fortran real*8). Fortran: 6 minutes, Java 33 minutes, same machine. jvisualm profiling shows much time spent in RealMatrixImpl.{getEntry,isValidCoordinate} (which appear to be gone in unreleased Apache commons math 2.0, but 2.0 is no faster). Fortran is using Atlas BLAS routines (dpotrf, etc.). Obviously this could depend on our code in each language, but we believe most of the time is in equivalent matrix operations. In several other computations that do not involve libraries, Java has not been much slower, and sometimes much faster.

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• 1k of Program Space, 64 bytes of RAM. Is assembly an absolute must?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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• Calculate an Internet (aka IP, aka RFC791) checksum in C#

  - by Pat

  Interestingly, I can find implementations for the Internet Checksum in almost every language except C#. Does anyone have an implementation to share? Remember, the internet protocol specifies that: "The checksum field is the 16 bit one's complement of the one's complement sum of all 16 bit words in the header. For purposes of computing the checksum, the value of the checksum field is zero." More explanation can be found from Dr. Math. There are some efficiency pointers available, but that's not really a large concern for me at this point. Please include your tests! (Edit: Valid comment regarding testing someone else's code - but I am going off of the protocol and don't have test vectors of my own and would rather unit test it than put into production to see if it matches what is currently being used! ;-) Edit: Here are some unit tests that I came up with. They test an extension method which iterates through the entire byte collection. Please comment if you find fault in the tests. [TestMethod()] public void InternetChecksum_SimplestValidValue_ShouldMatch() { IEnumerable<byte> value = new byte[1]; // should work for any-length array of zeros ushort expected = 0xFFFF; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); } [TestMethod()] public void InternetChecksum_ValidSingleByteExtreme_ShouldMatch() { IEnumerable<byte> value = new byte[]{0xFF}; ushort expected = 0xFF; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); } [TestMethod()] public void InternetChecksum_ValidMultiByteExtrema_ShouldMatch() { IEnumerable<byte> value = new byte[] { 0x00, 0xFF }; ushort expected = 0xFF00; ushort actual = value.InternetChecksum(); Assert.AreEqual(expected, actual); }

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• tips for fixing bad coding/dev habits ?

  - by dfafa

  i want to become a better coder....so i have decided to sign up for computing science program...maybe a formal education can assist me. i started working on smaller projects to learn but currently i have really bad coding/dev habits which is hindering my productivity as the codebase increases.... i have highlighted them and perhaps someone could make suggestions (or redirect to resources) or a more efficient method. most stuff that i made in the past were web apps. i usually develop with putty + nano...i just love the minimalist feel i use winscp and develop directly on my private web server...too lazy to do it on localhost and upload it later. i dont use subversion control...which one do i need ? sometimes ctrl +z doesn't work well. when i run out of ideas for naming variable, i use swear words instead. i swear a lot when i get stuck....how to deal with anger issue ? my codes look ugly with comments everywhere. would rather use procedural coding finds "thinking" in OO difficult and time consuming i "write first think later". refactors code only if i am getting paid for it. dislikes configuring linux distro, Apache, MySQL, scaling, designing graphics and layouts. does not like writing tests likes working alone. does not like sharing codes. has an econ degree dislikes reading other people's code would rather write it on my own it seems my only true desire is to translate my ideas to a working prototype as fast as possible....it seems like i am very uninterested in the other details...could it be that i am not cut out to be a coder after all ? is going back to study comp sci a bad idea ?

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• Using game of life or other virtual environment for artificial (intelligence) life simulation? [clos

  - by Berlin Brown

  One of my interests in AI focuses not so much on data but more on biologic computing. This includes neural networks, mapping the brain, cellular-automata, virtual life and environments. Described below is an exciting project that includes develop a virtual environment for bots to evolve in. "Polyworld is a cross-platform (Linux, Mac OS X) program written by Larry Yaeger to evolve Artificial Intelligence through natural selection and evolutionary algorithms." http://en.wikipedia.org/wiki/Polyworld " Polyworld is a promising project for studying virtual life but it still is far from creating an "intelligent autonomous" agent. Here is my question, in theory, what parameters would you use create an AI environment? Possibly a brain environment? Possibly multiple self contained life organisms that have their own "brain" or life structures. I would like a create a spin on the game of life simulation. What if you have a 64x64 game of life grid. But instead of one grid, you might have N number of grids. The N number of grids are your "life force" If all of the game of life entities die in a particular grid then that entire grid dies. A group of "grids" makes up a life form. I don't have an immediate goal. First, I want to simulate an environment and visualize what is going on in the environment with OpenGL and see if there are any interesting properties to the environment. I then want to add "scarce resources" and see if the AI environment can manage resources adequately.

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• how would you like computer science classes to be taught?

  - by aaa

  hello I am a graduate student now, and hopefully someday I will teach. my interests are C++, Python, embedded languages, and scientific computing. Meanwhile I daydream about how I would teach. I was not quite happy with my undergraduate university as I found many computer science classes lacking. so I would like to ask you, if you were a student, how would you like your computer science classes to be taught? I understand it is a very subjective question, but nevertheless I think it's important to know what people want. Some specific points I am interested in: should computer languages be taught explicitly, or should students be required to pick up language on their own? what is better for learning, tests, projects, some sort of take-home exam? how do you think classtime should be used? theory, introduction, explanations, etc.? do you think the group projects are important? how much about computer architecture do you want to learn in computer science class, not necessarily assembler class. should particular operating system/editor be mandated or encouraged? Thanks thank you for your comments. Question has been closed because it is a discussion question rather than Q&A. If you know appropriate website for discussions of such sort with low noise ratio, please let me know.

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• 1k of Program Space, 64 bytes of RAM. Is 1 wire communication possible?

  - by Earlz

  (If your lazy see bottom for TL;DR) Hello, I am planning to build a new (prototype) project dealing with physical computing. Basically, I have wires. These wires all need to have their voltage read at the same time. More than a few hundred microseconds difference between the readings of each wire will completely screw it up. The Arduino takes about 114 microseconds. So the most I could read is 2 or 3 wires before the latency would skew the accuracy of the readings. So my plan is to have an Arduino as the "master" of an array of ATTinys. The arduino is pretty cramped for space, but it's a massive playground compared to the tinys. An ATTiny13A has 1k of flash ROM(program space), 64 bytes of RAM, and 64 bytes of (not-durable and slow) EEPROM. (I'm choosing this for price as well as size) The ATTinys in my system will not do much. Basically, all they will do is wait for a signal from the Master, and then read the voltage of 1 or 2 wires and store it in RAM(or possibly EEPROM if it's that cramped). And then send it to the Master using only 1 wire for data.(no room for more than that!). So far then, all I should have to do is implement trivial voltage reading code (using built in ADC). But this communication bit I'm worried about. Do you think a communication protocol(using just 1 wire!) could even be implemented in such constraints? TL;DR: In less than 1k of program space and 64 bytes of RAM(and 64 bytes of EEPROM) do you think it is possible to implement a 1 wire communication protocol? Would I need to drop to assembly to make it fit? I know that currently my Arduino programs linking to the Wiring library are over 8k, so I'm a bit concerned.

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