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  • Converting EBNF to BNF

    - by Vivin Paliath
    It's been a few years since my computer-language class and so I've forgotten the finer points of BNF's and EBNF's and I don't have a textbook next to me. Specifically, I've forgotten how to convert an EBNF into BNF. From what little I remember, I know that one of the main points is to convert { term } into <term> | <many-terms>. But I don't remember the other rules. I've tried to look this up online but I can only find links to either homework questions, or a small comment about converting terms with curly braces. I can't find an exhaustive list of rules that define the translation.

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  • I dont understand Access modifiers in OOP (JAVA)

    - by Imran
    I know this is a silly question but 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 whats 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'm simply trying to understand why we do this? Thank you in advance;-)

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  • Dijkstra’s algorithms - a complete list

    - by baris_a
    Hi guys, I have recently asked a question about one of the Dijkstra’s algorithms. But, almost everyone thought it was shortest path. Therefore, I opened this post to gather all the algorithms that were invented by Dijkstra. Please add any if you know. Thanks in advance. 1 ) Shunting-yard algorithm

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  • netlogo programming question - catalyst implementation part 2

    - by user286190
    hi the catalyst speeds up the reaction but remains unchanged after the reaction has taken place i tried the following code breed [catalysts catalyst] breed [chemical-x chemical-x] ;then the forward reaction is sped up by the existence of catalysts to react-forward let num-catalysts count catalysts ;speed up by num-catalysts ;... end and it works fine but I want to make it so that the catalyst can be switched on and off with the 'switch' button ..so one can see the effects with and without the catalyst..i tried putting a switch in but catalyst has already been defined Also i want to make the catalyst visible so one can see it in the actual implementation (in the world) like making it a turtle is there are another way to implement this apart from using breeds i tried making the catalyst a turtle but it doesnt work ; Make catalyst visible in implementation clear-all crt catalysts 100 ask catalysts [ set color white ] show [breed] of one-of catalysts ; prints catalysts any help will be greatly appreciated thank you

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  • Papers on Software Methodology recommendation

    - by kunjaan
    Please recommend me software engineering/methodology/practices paper. So far I have enjoyed: 1968 Dijkstra : Go To Statement Considered Harmful Reason about correctness about program Nikalus Wirth : Program Development by Stepwise Refinement Not worried about program structure 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 Structures 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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  • How do I work out IEEE 754 64-bit Floating Point Double Precision?

    - by yousef gassar
    enter code herehello i have done it in 32 but i could dont do it in 62bits please i need help I am stuck on this question and need help. I don't know how to work it out. This is the question. Below are two numbers represented in IEEE 754 64-bit Floating Point Double Precision, the bias of the signed exponent is -1023. Any particular real number ‘N’ represented in 64-bit form (i.e. with the following bit fields; 1-bit Sign, 11-bit Exponent, 52-bit Fraction) can be expressed in the form ±1.F2 × 2X by substituting the bit-field values using formula (IV.I): N = (-1) S × 1.F2 × 2(E – 1023) for 0 < E < 2047.........................….(IV.I) Where N= the number represented, S=Sign bit-value, E=Exponent=X +1023, F=Fraction or Mantissa are the values in the 1, 11 and 52-bit fields respectively in the IEEE 754 64-bit FP representation. Using formula (IV.I), express the 64-bit FP representation of each number as: (i) A binary number of the form:- ±1.F2 × 2X (ii) A decimal number of the form:- ±0.F10 × 10Y {limit F10 to 10 decimal places} Sign 0 1 Exponent 1000 0001 001 11 Fraction 1111 0111 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 52 Sign 1 1 Exponent 1000 0000 000 11 Fraction 1001 0010 0001 1111 1011 0101 0100 0100 0100 0010 1101 0001 1000 52 I know I have to use the formula for each of the these but how do I work it out? Is it like this? N = (-1) S × 1.F2 × 2(E – 1023) = 1 x 1.1111 0111 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 0000 x 1000 0001 00111 (-1023)?

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  • Theory of Computation - Showing that a language is regular..

    - by Tony
    I'm reviewing some notes for my course on Theory of Computation and I'm a little bit stuck on showing the following statement and I was hoping somebody could help me out with an explanation :) Let A be a regular language. The language B = {ab | a exists in A and b does not exist in A*} Why is B a regular language? Some points are obvious to me. If b is simply a constant string, this is trivial. Since we know a is in A and b is a string, regular languages are closed under union, so unioning the language that accepts these two strings is obviously regular. I'm not sure that b is constant, however. Maybe it is, and if so, then this isn't really an issue. I'm having a hard time making sense of it. Thanks!

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  • Turing Model Vs Von Neuman model

    - by Santhosh
    First some background (based on my understanding).. The Von-Neumann architecture describes the stored-program computer where instructions and data are stored in memory and the machine works by changing it's internal state, i.e an instruction operated on some data and modifies the data. So inherently, there is state msintained in the system. The Turing machine architecture works by manipulating symbols on a tape. i.e A tape with infinite number of slots exists, and at any one point in time, the Turing machine is in a particular slot. Based on the symbol read at that slot, the machine change the symbol and move to a different slot. All of this is deterministic. My questions are Is there any relation between these two models (Was the Von Neuman model based on or inspired by the Turing model)? Can we say that Turing model is a superset of Von Newman model? Does functional Programming fit into Turing model. If so how? (I assume FP does not lend itself nicely to the Von Neuman model)

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

    - by smwikipedia
    I heard a lot that modern computers are based on Turing machine. I just cannot build a bridge between a conceptual Turing Machine and a 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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  • Recommended Math textbooks for programmers

    - by Tony
    I learned math in a non-English environment, I recently read some books about algorithm analysis, I found some math concepts were confusing, and seemed not the same as what I've learned. What math textbooks would you recommend that covers math concepts from the scratch and suitable for self-learning ?

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  • Evolutionary Algorithms: Optimal Repopulation Breakdowns

    - by Brian MacKay
    It's really all in the title, but here's a breakdown for anyone who is interested in Evolutionary Algorithms: In an EA, the basic premise is that you randomly generate a certain number of organisms (which are really just sets of parameters), run them against a problem, and then let the top performers survive. You then repopulate with a combination of crossbreeds of the survivors, mutations of the survivors, and also a certain number of new random organisms. Do that several thousand times, and efficient organisms arise. Some people also do things like introduce multiple "islands" of organisms, which are seperate populations that are allowed to crossbreed once in awhile. So, my question is: what are the optimal repopulation percentages? I have been keeping the top 10% performers, and repopulating with 30% crossbreeds and 30% mutations. The remaining 30% is for new organisms. I have also tried out the multiple island theory, and I'm interested in your results on that as well. It is not lost on me that this is exactly the type of problem an EA could solve. Are you aware of anyone trying that? Thanks in advance!

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  • What is a 'Closure'?

    - by Ben
    I asked a question about Currying and closures where mentioned. What is a closure? How does it relate to currying? Additional: Kyle's answer is great but to my poor procedural/OO mind Ben Childs answer is really useful.

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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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  • 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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  • 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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  • 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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