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  • What are 'len', 'dir', 'vars' named?

    - by johannix
    I was wondering what language to use when talking about a function that takes in a specific object, acts on it and returns something else. Clearly they're functions, but I was wondering if there's a more specific term. A couple examples of Python built-in functions that fit this spec are: 'len', 'dir', 'vars' I thought it was 'predicate', but apparently that's specific to functions that return a boolean value.

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  • What is the relationship between Turing Machine & Modern Computer ?

    - by smwikipedia
    I heard a lot that modern computers are based on Turing machine. I just cannot build a bridge from a conceptual Turing Machine to a real modern computer. Could someone help me build this bridge? Below is my current understanding. I think the computer is a big general-purpose Turing machine. Each program we write is a small specific-purpose Turing machine. The classical Turing machine do its job based on the input and its current state inside and so do our programs. Let's take a running program (a process) as an example. We know that in the process's address space, there's areas for stack, heap, and code. A classical Turing machine doesn't have the ability to remember many things, so we borrow the concept of stack from the push-down automaton. The heap and stack areas contains the state of our specific-purpose Turing machine (our program). The code area represents the logic of this small Turing machine. And various I/O devices supply input to this Turing machine.

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  • Why do we need different CPU architecture for server & mini/mainframe & mixed-core?

    - by claws
    Hello, I was just wondering what other CPU architectures are available other than INTEL & AMD. So, found List of CPU architectures on Wikipedia. It categorizes notable CPU architectures into following categories. Embedded CPU architectures Microcomputer CPU architectures Workstation/Server CPU architectures Mini/Mainframe CPU architectures Mixed core CPU architectures I was analyzing the purposes and have few doubts. I taking Microcomputer CPU (PC) architecture as reference and comparing others. Embedded CPU architecture: They are a completely new world. Embedded systems are small & do very specific task mostly real time & low power consuming so we do not need so many & such wide registers available in a microcomputer CPU (typical PC). In other words we do need a new small & tiny architecture. Hence new architecture & new instruction RISC. The above point also clarifies why do we need a separate operating system (RTOS). Workstation/Server CPU architectures I don't know what is a workstation. Someone clarify regarding the workstation. As of the server. It is dedicated to run a specific software (server software like httpd, mysql etc.). Even if other processes run we need to give server process priority therefore there is a need for new scheduling scheme and thus we need operating system different than general purpose one. If you have any more points for the need of server OS please mention. But I don't get why do we need a new CPU Architecture. Why cant Microcomputer CPU architecture do the job. Can someone please clarify? Mini/Mainframe CPU architectures Again I don't know what are these & what miniframes or mainframes used for? I just know they are very big and occupy complete floor. But I never read about some real world problems they are trying to solve. If any one working on one of these. Share your knowledge. Can some one clarify its purpose & why is it that microcomputer CPU archicture not suitable for it? Is there a new kind of operating system for this too? Why? Mixed core CPU architectures Never heard of these. If possible please keep your answer in this format: XYZ CPU architectures Purpose of XYZ Need for a new architecture. why can't current microcomputer CPU architecture work? They go upto 3GHZ & have upto 8 cores. Need for a new Operating System Why do we need a new kind of operating system for this kind of archictures?

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  • Searching, Sorting and Graph Algorithms questions

    - by user177883
    Is there a resource that i can find different variations of searching, sorting and graph algorithm questions ? I have studied CLRS and Algorithm Design by Kleinberg. and solved some set of questions. I have also, checked SO for algorithms questions. Curious, if there is a resource you would highly recommend. EDIT: There is also this free ebook with many questions, that i was able to solve some of them.

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  • Netlogo programming question - is it possible to put balanced chemical equations in a model?

    - by user286190
    hi I was wondering if it was possible to put balanced chemical equations, and if possible including state symbols, in the existing netlogo model that i am using, i havenot seen any examples in the models library so was not sure if it was possible. I wanted the model to be able to allow the user to input a balanced chemical equilibrium equation, or the model displays the the equation so then the user can select from them if they do not want to enter their own any help will be greatly appreciated thanks for example ethane + oxygen -- carbon dioxide + steam C2H6 + O2 -- CO2 + H2O

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  • merge sort recursion tree height

    - by Tony
    Hello! I am learning about recursion tree's and trying to figure out how the height of the tree is log b of n where n = 2 and one has 10 elements as input size. I am working with Merge sort. The number of times the split is done is the height of the tree as far as I understood, and the number of levels in the tree is height + 1. But if you take (for merge sort) log2 of 10 you get 1, where if you draw the tree you get at least 2 times that the recursion occurs. Where have I gone wrong? (I hope I am making sense here) NOTE: I am doing a self study, this is not homework!

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  • Software Engineering Papers

    - by kunjaan
    Please recommend me software engineering/methodology/practices paper. So far I have enjoyed: 1968 Dijkstra : Go To Statement Considered Harmful Nikalus Wirth : Program Development by Stepwise Refinement 1971 David Parnas : Information Distribution Aspects of Design Methodology 1972 Liskov : Design Methodology for Reliable Software Systems Extensible Language : Schuman and P Jourrand R. Balzer Structured Programming : Dahl - Hierarchical Program StructuresImplementation Patterns 1971 Jim Morris Protection in Programming Languages 1973 Bill Wulf and Mary Shaw Global Variable Considered Harmful 1974 : Lisko and Zilles ADTs

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  • Is there any need to get a Computer Science degree?

    - by Tom Moseley
    I've been a software developer for 20 years. i've been involved in language development and large data warehouse development. I've worked for start-ups that have gone public, and for government contractors, and I've written a published programming book. My knowledge is either self-taught or on-the-job. I've worked with some of the best and brightest, and they taught me well. I'm back in school now, and am weighing my options, deciding between a Computer Science and a business degree. My question is this. What do I gain, at this point in my career, by earning a Computer Science degree? I just don't know if a Computer Science degree, at this point, is a value-add on my resume. Edit: I'm working on completing an undergraduate degree.

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  • Power of programming languages

    - by Casebash
    Are there any objective measures for measuring the power of programming languages? Turing-completeness is one, but it is not particularly discriminating. I also remember there being a few others measures of power which are more limited versions (like finite-state-autonoma), but is there any objective measure that is more powerful?

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  • Proving that P <= NP

    - by Gail
    As most people know, P = NP is unproven and seems unlikely to be true. The proof would prove that P <= NP and NP <= P. Only one of those is hard, though. P <= NP is almost by definition true. In fact, that's the only way that I know how to state that P <= NP. It's just intuitive. How would you prove that P <= NP?

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  • CS 50- Pset 1 Mario Program

    - by boametaphysica
    the problem set asks us to create a half pyramid using hashes. Here is a link to an image of how it should look- I get the idea and have written the program until printing the spaces (which I have replaced by "_" just so that I can test the first half of it. However, when I try to run my program, it doesn't go beyond the do-while loop. In other words, it keeps asking me for the height of the pyramid and does not seem to run the for loop at all. I've tried multiple approaches but this problem seems to persist. Any help would be appreciated! Below is my code- # include <cs50.h> # include <stdio.h> int main(void) { int height; do { printf("Enter the height of the pyramid: "); height = GetInt(); } while (height > 0 || height < 24); for (int rows = 1; rows <= height, rows++) { for (int spaces = height - rows; spaces > 0; spaces--) { printf("_"); } } return 0; } Running this program yields the following output- Enter the height of the pyramid: 11 Enter the height of the pyramid: 1231 Enter the height of the pyramid: aawfaf Retry: 12 Enter the height of the pyramid:

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  • Complex behavior generated by simple computation

    - by Yuval A
    Stephen Wolfram gave a fascinating talk at TED about his work with Mathematica and Wolfram Alpha. Amongst other things, he pointed out how very simple computations can yield extremely complex behaviors. (He goes on to discuss his ambition for computing the entire physical universe. Say what you will, you gotta give the guy some credit for his wild ideas...) As an example he showed several cellular automata. What other examples of simple computations do you know of that yield fascinating results?

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  • Turing Machine & Modern Computer

    - by smwikipedia
    I heard a lot that modern computers are based on Turing machine. I'd like to share my understanding and hear your comments. I think the computer is a big general-purpose Turing machine. Each program we write is a small specific-purpose Turing machine. The classical Turing machine do its job based on the input and its current state inside and so do our programs. Let's take a running program (a process) as an example. We know that in the process's address space, there's areas for stack, heap, and code. A classical Turing machine doesn't have the ability to remember many things, so we borrow the concept of stack from the push-down automaton. The heap and stack areas contains the state of our specific-purpose Turing machine (our program). The code area represents the logic of this small Turing machine. And various I/O devices supply input to this Turing machine. The above is my naive understanding about the working paradigm of modern computer. I couln't wait to hear your comments. Thanks very much.

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  • Code Golf: Shortest Turing-complete interpreter.

    - by ilya n.
    I've just tried to create the smallest possible language interpreter. Would you like to join and try? Rules of the game: You should specify a programming language you're interpreting. If it's a language you invented, it should come with a list of commands in the comments. Your code should start with example program and data assigned to your code and data variables. Your code should end with output of your result. It's preferable that there are debug statements at every intermediate step. Your code should be runnable as written. You can assume that data are 0 and 1s (int, string or boolean, your choice) and output is a single bit. The language should be Turing-complete in the sense that for any algorithm written on a standard model, such as Turing machine, Markov chains, or similar of your choice, it's reasonably obvious (or explained) how to write a program that after being executred by your interpreter performs the algorithm. The length of the code is defined as the length of the code after removal of input part, output part, debug statements and non-necessary whitespaces. Please add the resulting code and its length to the post. You can't use functions that make compiler execute code for you, such as eval(), exec() or similar. This is a Community Wiki, meaning neither the question nor answers get the reputation points from votes. But vote anyway!

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  • Access modifiers in Object-Oriented Programming

    - by Imran
    I don't understand Access Modifiers in OOP. Why do we make for example in Java instance variables private and then use public getter and setter methods to access them? I mean what's the reasoning/logic behind this? You still get to the instance variable but why use setter and getter methods when you can just make your variables public? please excuse my ignorance as I am simply trying to understand why? Thank you in advance. ;-)

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  • Netlogo Programming question - Chemical Equilibrium temperature and pressure implementation

    - by user286190
    Hi I am trying to code something in Netlogo..I am using an existing model Chemical Equilibrium and am trying to implement the following: turtles-own [speed ] ask turtles [ ;; set velocity ( ambient-temperature = 30 ) ;; fd velocity if temp > 40 [ "speed" increases of turtles ] ifelse temperature < 30 [ speed of turtles decreases] ] ;; to temp but it does not seem to work (it temperature is more than 40 the speed of the turtles increases if the temperature is less than 30 the speed of the turtles decreases) temperature is a slider on the model the same for pressure ask turtles [ ;; if pressure > 50 then speed increases of turtles ;; if pressure < 50 then speed decreases of turtles ] ;; to pressure thanks

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  • Can Haskell's Parsec library be used to implement a recursive descent parser with backup?

    - by Thor Thurn
    I've been considering using Haskell's Parsec parsing library to parse a subset of Java as a recursive descent parser as an alternative to more traditional parser-generator solutions like Happy. Parsec seems very easy to use, and parse speed is definitely not a factor for me. I'm wondering, though, if it's possible to implement "backup" with Parsec, a technique which finds the correct production to use by trying each one in turn. For a simple example, consider the very start of the JLS Java grammar: Literal: IntegerLiteral FloatingPointLiteral I'd like a way to not have to figure out how I should order these two rules to get the parse to succeed. As it stands, a naive implementation like this: literal = do { x <- try (do { v <- integer; return (IntLiteral v)}) <|> (do { v <- float; return (FPLiteral v)}); return(Literal x) } Will not work... inputs like "15.2" will cause the integer parser to succeed first, and then the whole thing will choke on the "." symbol. In this case, of course, it's obvious that you can solve the problem by re-ordering the two productions. In the general case, though, finding things like this is going to be a nightmare, and it's very likely that I'll miss some cases. Ideally, I'd like a way to have Parsec figure out stuff like this for me. Is this possible, or am I simply trying to do too much with the library? The Parsec documentation claims that it can "parse context-sensitive, infinite look-ahead grammars", so it seems like something like I should be able to do something here.

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  • Dynamic programming solution to the subset-sum decision problem

    - by Gail
    How can a dynamic programming solution for the unbounded knapsack decision problem be used to come up with a dynamic programming solution to the subset-sum decision problem? This limitation seems to render the unbounded knapsack problem useless. In the unbounded knapsack, we simply store true or false for if some subset of integers sum up to our target value. However, if we have a limit on the frequency of the use of these integers, the optimal substructure at least appears to fail. How can this be done?

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  • Is the Unix Philosophy still relevant in the Web 2.0 world?

    - by David Titarenco
    Introduction Hello, let me give you some background before I begin. I started programming when I was 5 or 6 on my dad's PSION II (some primitive BASIC-like language), then I learned more and more, eventually inching my way up to C, C++, Java, PHP, JS, etc. I think I'm a pretty decent coder. I think most people would agree. I'm not a complete social recluse, but I do stuff like write a virtual machine for fun. I've never taken a computer course in college because I've been in and out for the past couple of years and have only been taking core classes; never having been particularly amazing at school, perhaps I'm missing some basic tenet that most learn in CS101. I'm currently reading Coders at Work and this question is based on some ideas I read in there. A Brief (Fictionalized) Example So a certain sunny day I get an idea. I hire a designer and hammer away at some C/C++ code for a couple of months, soon thereafter releasing silvr.com, a website that transmutes lead into silver. Yep, I started my very own start-up and even gave it a clever web 2.0 name with a vowel missing. Mom and dad are proud. I come up with some numbers I should be seeing after 1, 2, 3, 6, 9, 12 months and set sail. Obviously, my transmuting server isn't perfect, sometimes it segfaults, sometimes it leaks memory. I fix it and keep truckin'. After all, gdb is my best friend. Eventually, I'm at a position where a very small community of people are happily transmuting lead into silver on a semi-regular basis, but they want to let their friends on MySpace know how many grams of lead they transmuted today. And they want to post images of their lead and silver nuggets on flickr. I'm losing out on potential traffic unless I let them log in with their Yahoo, Google, and Facebook accounts. They want webcam support and live cock fighting, merry-go-rounds and Jabberwockies. All these things seem necessary. The Aftermath Of course, I have to re-write the transmuting server! After all, I've been losing money all these months. I need OAuth libraries and OpenID libraries, JSON support, and the only stable Jabberwocky API is for Java. C++ isn't even an option anymore. I'm just one guy! The Java binary just grows and grows since I need some legacy Apache include for the JSON library, and some antiquated Sun dependency for OAuth support. Then I pick up a book like Coders at Work and read what people like jwz say about complexity... I think to myself.. Keep it simple, stupid. I like simple things. I've always loved the Unix Philosophy but even after trying to keep the new server source modular and sleek, I loathe having to write one more line of code. It feels that I'm just piling crap on top of other crap. Maybe I'm naive thinking every piece of software can be simple and clever. Maybe it's just a phase.. or is the Unix Philosophy basically dead when it comes to the current state of (web) development? I'm just kind of disheartened :(

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