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  • Recognizing terminals in a CFG production previously not defined as tokens.

    - by kmels
    I'm making a generator of LL(1) parsers, my input is a CoCo/R language specification. I've already got a Scanner generator for that input. Suppose I've got the following specification: COMPILER 1. CHARACTERS digit="0123456789". TOKENS number = digit{digit}. decnumber = digit{digit}"."digit{digit}. PRODUCTIONS Expression = Term{"+"Term|"-"Term}. Term = Factor{"*"Factor|"/"Factor}. Factor = ["-"](Number|"("Expression")"). Number = (number|decnumber). END 1. So, if the parser generated by this grammar receives a word "1+1", it'd be accepted i.e. a parse tree would be found. My question is, the character "+" was never defined in a token, but it appears in the non-terminal "Expression". How should my generated Scanner recognize it? It would not recognize it as a token. Is this a valid input then? Should I add this terminal in TOKENS and then consider an error routine for a Scanner for it to skip it? How does usual language specifications handle this?

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  • What is the best way to become a professional in PHP and Website Building?

    - by Mr.TAMER
    I would like to become a professional in php, I have learned nearly all about the language syntax and concepts and I have a good knowledge in C and C++, which made it easier to become familiar with PHP. (Of course, I learned MySql too.) But I don't feel like being able to build even a little good website of my own! It looks like PHP is all about knowing lots of functions and using them, while in fact I don't think it's like that, is it? How can I become a professional in PHP and Website Building? I would do anything and spend whatever amount of time required for that. EDIT I've also a very good knowledge in HTML and a normal knowledge in CSS and JavaScript. Sorry for not mentioning that, I just thought it was implicitly included.

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  • recursion tree and binary tree cost calculation

    - by Tony
    Hi all, I've got the following recursion: T(n) = T(n/3) + T(2n/3) + O(n) The height of the tree would be log3/2 of 2. Now the recursion tree for this recurrence is not a complete binary tree. It has missing nodes lower down. This makes sense to me, however I don't understand how the following small omega notation relates to the cost of all leaves in the tree. "... the total cost of all leaves would then be Theta (n^log3/2 of 2) which, since log3/2 of 2 is a constant strictly greater then 1, is small omega(n lg n)." Can someone please help me understand how the Theta(n^log3/2 of 2) becomes small omega(n lg n)?

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  • Why is x86 ugly? aka Why is x86 considered inferior when compared to others?

    - by claws
    Hello, recently I've been reading some SO archives and encountered statements against x86 architecture. http://stackoverflow.com/questions/2667256/why-do-we-need-different-cpu-architecture-for-server-mini-mainframe-mixed-cor says "PC architecture is a mess, any OS developer would tell you that." http://stackoverflow.com/questions/82432/is-learning-assembly-language-worth-the-effort says "Realize that the x86 architecture is horrible at best" http://forums.anandtech.com/showthread.php?t=976577 says "Most colleges teach assembly on something like MIPS because it's much simpler to understand, x86 assembly is really ugly" and many more comments like Compared to most architectures, X86 sucks pretty badly. It's definitely the conventional wisdom that X86 is inferior to MIPS, SPARC, and PowerPC x86 is ugly I tried searching but didn't find any reasons. I don't find x86 bad probably because this is the only architecture I'm familiar with. Can someone kindly give me reasons for considering x86 ugly/bad/inferior compared to others.

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  • Unix tree convert to recursive php array

    - by Fordnox
    I have a response from remote server like this: /home/computer/Downloads |-- /home/computer/Downloads/Apple | `-- /home/computer/Downloads/Apple/Pad |-- /home/computer/Downloads/Empty_Folder `-- /home/computer/Downloads/Subfolder |-- /home/computer/Downloads/Subfolder/Empty `-- /home/computer/Downloads/Subfolder/SubSubFolder `-- /home/computer/Downloads/Subfolder/SubSubFolder/Test this is the output for command computer@athome:$ tree -df --noreport -L 5 /home/computer/Downloads/ I would like to parse this string to recursive php array or object, something like this. I would show only part of result to get the idea. array( 'title' => '/home/computer/Downloads', 'children' => array( 0 => array( 'title' => '/home/computer/Downloads/Apple', 'children' => array( ... ) ) ); Response from server can change according to scanned directory. Can someone help me write this function. Please note that this is response from remote server and php functions can not scan any remote dir.

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  • What are the lesser known but cool data structures ?

    - by f3lix
    There a some data structures around that are really cool but are unknown to most programmers. Which are they? Everybody knows linked lists, binary trees, and hashes, but what about Skip lists, Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I am also interested on techniques like Dancing links which make interesting use of the properties of a common data structure. EDIT: Please try to include links to pages describing the data structures in more detail. Also, try to add a couple of words on why a data structures is cool (as Jonas Kölker already pointed out). Also, try to provide one data-structure per answer. This will allow the better data structures to float to the top based on their votes alone.

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  • minimum enclosing rectangle of fixed aspect ratio

    - by Ramya Narasimha
    I have an Image with many rectangles at different positions in the image and of different sizes (both overlapping and non-overlapping). I also have a non-negative scores associated with each of these rectangles. My problem now is to find one larger rectangle *of a fixed (given) aspect ratio* that encloses as many of these rectangles as possible. I am looking for an algorithm to do this, if anyone has a solution, even a partial one it would be helpful. Please note that the positions of the rectangles in the image is fixed and cannot be moved around and there is no orientation issue as all of them are upright.

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  • The Definition of Regular Languages

    - by AraK
    Good Day, I have tried, and burned my brain to understand the definition of Regular Languages in Discrete Mathematics and its Applications(Rosen) without reaching the goal of understanding why the definition is like that in this book. On page(789), I am rephrasing the definition: Type 3 grammars are defined as: w1 --> w2 Where w1 is a non-terminal, and w2 is of the form: w2 = aB w2 = a Where B is a non-terminal, and a is a terminal. A special case is when w1 is the starting symbol and w2 is lambda(the empty string): w1 = S S --> lambda Two questions I couldn't find an answer for. First, Why can't w2 be of the form Ba. Second, Why lambda is only allowed for the starting symbol only. The book states that, regular languages are equivalent to Finite State Automaton, and we can easily see that a we can build FSA for both cases. I took a look at other resources, and these restrictions don't exist in these resources. Thanks,

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  • When does an ARM7 processor increase its PC register?

    - by Summer_More_More_Tea
    Hi everyone: I'm thinking about this question for a time: when does an ARM7(with 3 pipelines) processor increase its PC register. I originally thought that after an instruction has been executed, the processor first check is there any exception in the last execution, then increase PC by 2 or 4 depending on current state. If an exception occur, ARM7 will change its running mode, store PC in the LR of current mode and begin to process current exception without modifying the PC register. But it make no sense when analyzing returning instructions. I can not work out why PC will be assigned LR when returning from an undefined-instruction-exception while LR-4 from prefetch-abort-exception, don't both of these exceptions happened at the decoding state? What's more, according to my textbook, PC will always be assigned LR-4 when returning from prefetch-abort-exception no matter what state the processor is(ARM or Thumb) before exception occurs. However, I think PC should be assigned LR-2 if the original state is Thumb, since a Thumb-instruction is 2 bytes long instead of 4 bytes which an ARM-instruction holds, and we just wanna roll-back an instruction in current state. Is there any flaws in my reasoning or something wrong with the textbook. Seems a long question. I really hope anyone can help me get the right answer. Thanks in advance.

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  • Can you recommend a good tutorial on building custom package versions?

    - by Ivan
    After installing Ubuntu 11.04 I was disappointed by the fact there are still Scala 2.7 (when 2.8 is long ago current actual branch) and Mono 2.6 (when pretty a time has passed after 2.8 release). I am not sure I could build all the packages for Mono myself, but I'd like to try making my own custom version of Scala package (and I want my system to accept it not as a different package but a version of the original, so that if I put it into a configured repository, the system will automatically upgrade to it from currently installed original 2.7). Can you recommend a good tutorial on this subject (Ubuntu deb packages building and hacking for beginners)?

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  • How is a new programming language actually formed/created ?

    - by hory.incpp
    Fortran-Algol-Cpl-Bcpl-C-C++-Java ..... Seems like every language is built upon an ancestor language. My question : New languages extend parent ones or there is some kind of a trick? e.g. System.out.print() in Java ; is it actually printf() in C, and so on (printf is actually .. in Cpl)? If so, doesn't this make every further language be slower and need more memory? What separates a new language from a framework?

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  • Calculating rotation and translation matrices between two odometry positions for monocular linear triangulation

    - by user1298891
    Recently I've been trying to implement a system to identify and triangulate the 3D position of an object in a robotic system. The general outline of the process goes as follows: Identify the object using SURF matching, from a set of "training" images to the actual live feed from the camera Move/rotate the robot a certain amount Identify the object using SURF again in this new view Now I have: a set of corresponding 2D points (same object from the two different views), two odometry locations (position + orientation), and camera intrinsics (focal length, principal point, etc.) since it's been calibrated beforehand, so I should be able to create the 2 projection matrices and triangulate using a basic linear triangulation method as in Hartley & Zissermann's book Multiple View Geometry, pg. 312. Solve the AX = 0 equation for each of the corresponding 2D points, then take the average In practice, the triangulation only works when there's almost no change in rotation; if the robot even rotates a slight bit while moving (due to e.g. wheel slippage) then the estimate is way off. This also applies for simulation. Since I can only post two hyperlinks, here's a link to a page with images from the simulation (on the map, the red square is simulated robot position and orientation, and the yellow square is estimated position of the object using linear triangulation.) So you can see that the estimate is thrown way off even by a little rotation, as in Position 2 on that page (that was 15 degrees; if I rotate it any more then the estimate is completely off the map), even in a simulated environment where a perfect calibration matrix is known. In a real environment when I actually move around with the robot, it's worse. There aren't any problems with obtaining point correspondences, nor with actually solving the AX = 0 equation once I compute the A matrix, so I figure it probably has to do with how I'm setting up the two camera projection matrices, specifically how I'm calculating the translation and rotation matrices from the position/orientation info I have relative to the world frame. How I'm doing that right now is: Rotation matrix is composed by creating a 1x3 matrix [0, (change in orientation angle), 0] and then converting that to a 3x3 one using OpenCV's Rodrigues function Translation matrix is composed by rotating the two points (start angle) degrees and then subtracting the final position from the initial position, in order to get the robot's straight and lateral movement relative to its starting orientation Which results in the first projection matrix being K [I | 0] and the second being K [R | T], with R and T calculated as described above. Is there anything I'm doing really wrong here? Or could it possibly be some other problem? Any help would be greatly appreciated.

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  • Divide and conquer method to compute roots [SOLVED]

    - by hellsoul153
    Hello, Knowing that we can use Divide-and-Conquer algorithm to compute large exponents, for exemple 2 exp 100 = 2 exp(50) * 2 exp(50), which is quite more efficient, is this method efficient using roots ? For exemple 2 exp (1/100) = (2 exp(1/50)) exp(1/50) ? In other words, I'm wondering if (n exp(1/x)) is more efficient to (n exp(1/y)) for x < y and where x and y are integers.

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  • Building Enterprise Smartphone App &ndash; Part 2: Platforms and Features

    - by Tim Murphy
    This is part 2 in a series of posts based on a talk I gave recently at the Chicago Information Technology Architects Group.  Feel free to leave feedback. In the previous post I discussed what reasons a company might have for creating a smartphone application.  In this installment I will cover some of history and state of the different platforms as well as features that can be leveraged for building enterprise smartphone applications. Platforms Before you start choosing a platform to develop your solutions on it is good to understand how we got here and what features you can leverage. History To my memory we owe all of this to a product called the Apple Newton that came out in 1987. It was the first PDA and back then I was much more of an Apple fan.  I was very impressed with this device even though it never really went anywhere.  The Palm Pilot by US Robotics was the next major advancement in PDA. It had a simple short hand window that allowed for quick stylus entry.. Later, Windows CE came out and started the broadening of the PDA market. After that it was the Palm and CE operating systems that started showing up on cell phones and for some time these were the two dominant operating systems that were distributed with devices from multiple hardware vendors. Current The iPhone was the first smartphone to take away the stylus and give us a multi-touch interface.  It was a revolution in usability and really changed the attractiveness of smartphones for the general public.  This brought us to the beginning of the current state of the market with the concept of an online store that makes it easy for customers to get new features and functionality on demand. With Android, Google made this more than a one horse race.  Not only did they come to compete, their low cost actually made them the leading OS.  Of course what made Android so attractive also is its major fault.  It is so open that it has been a target for malware which leaves consumers exposed.  Fortunately for Google though, most consumers aren’t aware of the threat that they are under. Although Microsoft had put out one of the first smart phone operating systems with CE it had to play catch up and finally came out with the Windows Phone.  They have gone for a market approach between those of iOS and Android.  They support multiple hardware vendors like Google, but they kept a certification process for applications that is similar to Apple.  They also created a user interface that was different enough to give it a clear separation from the other two platforms. The result of all this is hundreds of millions of smartphones being sold monthly across all three platforms giving us a wide range of choices and challenges when it comes to developing solutions. Features So what are the features that make these devices flexible enough be considered for use in the enterprise? The biggest advantage of today's devices is network connectivity.  The ability to access information from multiple sources at a moment’s notice is critical for businesses.  Add to that the ability to communicate over a variety of text, voice and video modes and we have a powerful starting point. Every smartphone has a cameras and they are not just useful for posting to Instagram. We are seeing more applications such as Bing vision that allow us to scan just about any printed code or text to find information.  These capabilities have been made available to developers in the form of standard libraries for reading barcodes of just about an flavor and optical character recognition (OCR) interpretation. Bluetooth give us the ability to communicate with multiple devices. Whether these are headsets, keyboard or printers the wireless communication capabilities are just starting to evolve.  The more these wireless communication protocols grow, the more opportunities we will see to transfer data between users and a variety of devices. Local storage of information that can be called up even when the device cannot reach the network is the other big capability.  This give users the ability to work offline as well and transmit information when connections are restored. These are the tools that we have to work with to build applications that can be leveraged to gain a competitive advantage for companies that implement them. Coming Up In the third installment I will cover key concerns that you face when building enterprise smartphone apps. del.icio.us Tags: smartphones,enterprise smartphone Apps,architecture,iOS,Android,Windows Phone

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  • Do invariant assertions fit into C# programming?

    - by P.Brian.Mackey
    In the book coders at work, the author asks "How do you use invariants in your code". Please explain what this question means. I saw class invariants on wiki, but the example is in Java and I am not skilled enough in Java to relate this example to C#. .NET 4.0 introduces invariance, covariance, and contravariance and is well explained here. Invariance is so broad. The authors usage of the word seems unit test related. For those that read the book, what does the author mean? Are we talking about making an assumption and simply testing the validity after the unit test?

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  • How do I get rid of this drive mount confirmation question when booting the computer?

    - by Dave M G
    With help from this site, I was able to set up an SSHFS connection between two computers on my LAN so that one auto mounts on the other at boot time. Everything works, but there is this annoying confirmation that comes up whenever I boot: An error occurred while mounting /home/dave/Mythbuntu. Press S to skip mounting or M or Manual recovery If I press S, then booting continues, and my drive is mounted as hoped, so it seems like even though I "skipped" it, maybe it tried again and succeeded later in the boot process. I followed the instructions here to set up "if up / if down" scripts, and here is my current /etc/fstab: sshfs#[email protected]:/home/mythbuntu /home/dave/Mythbuntu fuse auto,users,exec,uid=1000,gid=1000,allow_other,reconnect,transform_symlinks,BatchMode=yes 0 0 Although the mounting is working, this step of having to press S every time I boot is obviously kind of a hassle. How do I configure my computer so I don't have to do that, and so that my other computer will still automount?

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  • Why does my computer just keep restarting while trying to install Ubuntu 13.04 (x86) from USB alongside Windows 7?

    - by Sumit Chahal
    I have checked the other questions, but none of them match my problem (the ones that do don't have satisfactory answers). I downloaded the Ubuntu 13.04 iso and burned it to my USB device following the given instructions. I was also able to boot the Ubuntu setup from it by changing the boot sequence so that the USB device is now at the top. But I am only able to use the "trial" version of Ubuntu. Every time I tick "Install Ubuntu alongside Windows" and click "Continue", the computer just restarts and I see the same Try-Ubuntu-or-install-it menu. I have tried pressing any key when that little icon appears at the bottom, but it is not at all helpful. I also read somewhere that I should eject my USB device after I click "Continue", but doing so just makes the computer run Windows 7 instead.

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  • Is it possible to have regexp that matches all valid regular expressions?

    - by Juha Syrjälä
    Is it possible to detect if a given string is valid regular expression, using just regular expressions? Say I have some strings, that may or may not be a valid regular expressions. I'd like to have a regular expression matches those string that correspond to valid regular expression. Is that possible? Or do I have use some higher level grammar (i.e. context free language) to detect this? Does it affect if I am using some extended version of regexps like Perl regexps? If that is possible, what the regexp matching regexp is?

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  • Algorithm for optimally choosing actions to perform a task

    - by Jules
    There are two data types: tasks and actions. An action costs a certain time to complete, and a set of tasks this actions consists of. A task has a set of actions, and our job is to choose one of them. So: class Task { Set<Action> choices; } class Action { float time; Set<Task> dependencies; } For example the primary task could be "Get a house". The possible actions for this task: "Buy a house" or "Build a house". The action "Build a house" costs 10 hours and has the dependencies "Get bricks" and "Get cement", etcetera. The total time is the sum of all the times of the actions required to perform. We want to choose actions such that the total time is minimal. Note that the dependencies can be diamond shaped. For example "Get bricks" could require "Get a car" (to transport the bricks) and "Get cement" would also require a car. Even if you do "Get bricks" and "Get cement" you only have to count the time it takes to get a car once. Note also that the dependencies can be circular. For example "Money" - "Job" - "Car" - "Money". This is no problem for us, we simply select all of "Money", "Job" and "Car". The total time is simply the sum of the time of these 3 things. Mathematical description: Let actions be the chosen actions. valid(task) = ?action ? task.choices. (action ? actions ? ?tasks ? action.dependencies. valid(task)) time = sum {action.time | action ? actions} minimize time subject to valid(primaryTask)

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  • What is the most easy way to get in advanced Type Theory.

    - by Bubba88
    Of course, by 'advanced' I mean here just something beyond what every programmer does know. I'm currently more-or-less comfortable with the basics and want to understand the most important, most elegant and most practically applicable achievements of modern type theory. I just do not have much time, desire and mental powers to study all the formalistics more thoroughly and that may change in the future. But there is something really attractive for me in that branch, that just forces to ask silly questions like this :) Thank you very much!

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  • How to setup Ubuntu as a backup server for my Windows computer?

    - by derek
    I took my old computer (AMD 5600+, 2GB RAM, 880gt, 250GB SATA, etc) and decided to jump and try Ubuntu for the first time. I have very very little knowledge (Red Hat when I was younger) with Linux in general. My main desktop is Windows 7 and my plan is to use the Ubuntu computer as a file server sort of speak. I want to be able to setup back up schedules from my Windows PC to the Ubuntu PC (plan on leaving this on 24/7 to double as a Seedbox) How do I go on to doing this?

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  • portfolio building, working for closed-source vs open-source?

    - by jondavidjohn
    I've currently graduated from my first run at higher education, landed my first full-time gig as a web application developer, and absolutely love it. My question is that in looking for jobs I ran across many jobs that require a certain level of experience and code examples. Much of the work I am doing is both protected by a login, and closed source. How does someone, that is just starting out and needs to be building a resume, go about preparing for the next job. (no matter how much i love my current job, i feel like it's only responsible to always be preparing)

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