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  • O(log N) == O(1) - Why not?

    - by phoku
    Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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  • maximum memory which malloc can allocate!

    - by Vikas
    I was trying to figure out how much memory I can malloc to maximum extent on my machine (1 Gb RAM 160 Gb HD Windows platform). I read that maximum memory malloc can allocate is limited to physical memory.(on heap) Also when a program exceeds consumption of memory to a certain level, the computer stops working because other applications do not get enough memory that they require. So to confirm,I wrote a small program in C, int main(){ int *p; while(1){ p=(int *)malloc(4); if(!p)break; } } Hoping that there would be a time when memory allocation will fail and loop will be breaked. But my computer hanged as It was an infinite loop. I waited for about an hour and finally I had to forcely shut down my computer. Some questions: Does malloc allocate memory from HD also? What was the reason for above behaviour? Why didn't loop breaked at any point of time.? Why wasn't there any allocation failure?

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  • Creating a "mountable" File System, where to start?

    - by Mike Curry
    A friend and I are thinking about creating a simple file system for learning purposes. We're going to write it in C/C++, and try to get it to a mountable state from within linux. We've both been coding or over 16 years (32 combined), so I suppose its just a matter of finding some documentation, and a ton of learning. My question is, where could I find out more information? (Documentation for creating a file system, requirements of mounting a file system in linux, etc) Where do we start? Edit: I should also mention, this would not be a boot-able file system, just a file system used for storage, though I am not too sure if that matters or not.

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  • how to merge file lines having the same first word in python?

    - by user1377135
    I have written a program to merge lines in a file containing the same first word in python. However I am unable to get the desired output. Can anyone please suggest me the mistake in my program? input "file.txt" line1: a b c line2: a b1 c1 line3: d e f line4: i j k line5: i s t line6: i m n ` output a b c a b1 c1 d e f i j k i s t i m n my code a = [line.split() for line in open('file.txt')] L=[] for i in range(0,len(a)): j=i while True: if a[j][0] == a[j+1][0]: L.append(a[j]) L.append(a[j+1]) j=j+2 else: print a[i] print L break

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  • UV-vis detector [Hardware]

    - by aaa
    hello. This is not hundred percent programming related question, but I was not able to find answer on the net. Is there some kind of detector to record frequency/intensity of light radiation source? something like spectroscopy detector, but instead of actual machine, just the module which can be integrated in project. I have tried searching on Google but I do not even know what such device is called if you know the more appropriate place to ask, can you let me know please. Thank you

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  • Three most critical programming concepts

    - by Todd
    I know this has probably been asked in one form or fashion but I wanted to pose it once again within the context of my situation (and probably others here @ SO). I made a career change to Software Engineering some time ago without having an undergrad or grad degree in CS. I've supplemented my undergrad and grad studies in business with programming courses (VB, Java,C, C#) but never performed academic coursework in the other related disciplines (algorithms, design patterns, discrete math, etc.)...just mostly self-study. I know there are several of you who have either performed interviews and/or made hiring decisions. Given recent trends in demand, what would you say are the three most essential Comp Sci concepts that a developer should have a solid grasp of outside of language syntax? For example, I've seen blog posts of the "Absolute minimum X that every programmer must know" variety...that's what I'm looking for. Again if it's truly a redundancy please feel free to close; my feelings won't be hurt. (Closest ones I could find were http://stackoverflow.com/questions/164048/basic-programming-algorithmic-concepts- which was geared towards a true beginner, and http://stackoverflow.com/questions/648595/essential-areas-of-knowledge-which I didn't feel was concrete enough). Thanks in advance all! T.

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  • Convert a post-order binary tree traversal index to an level-order (breadth-first) index

    - by strfry
    Assuming a complete binary tree, each node can be adressed with the position it appears in a given tree traversal algorithm. For example, the node indices of a simple complete tree with height 3 would look like this: breadth first (aka level-order): 0 / \ 1 2 / \ / \ 3 4 5 6 post-order dept first: 6 / \ 2 5 / \ / \ 0 1 3 4 The height of the tree and an index in the post-order traversal is given. How can i calculate the breadth first index from this information?

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  • Standard term for a thread I/O reorder buffer?

    - by Crashworks
    I have a case where many threads all concurrently generate data that is ultimately written to one long, serial file. I need to somehow serialize these writes so that the file gets written in the right order. ie, I have an input queue of 2048 jobs j0..jn, each of which produces a chunk of data oi. The jobs run in parallel on, say, eight threads, but the output blocks have to appear in the file in the same order as the corresponding input blocks — the output file has to be in the order o0o1o2... The solution to this is pretty self evident: I need some kind of buffer that accumulates and writes the output blocks in the correct order, similar to a CPU reorder buffer in Tomasulo's algorithm, or to the way that TCP reassembles out-of-order packets before passing them to the application layer. Before I go code it, I'd like to do a quick literature search to see if there are any papers that have solved this problem in a particularly clever or efficient way, since I have severe realtime and memory constraints. I can't seem to find any papers describing this though; a Scholar search on every permutation of [threads, concurrent, reorder buffer, reassembly, io, serialize] hasn't yielded anything useful. I feel like I must just not be searching the right terms. Is there a common academic name or keyword for this kind of pattern that I can search on?

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  • CS Majors: Hardest concept(s) you learned in school?

    - by Mark Lubin
    For the CS majors out there what were the hardest CS classes or concepts that you learned in your undergraduate schooling? Did you find once you learned the basics,(data structs, OOP fundamentals, discrete math, pointers, recursion, etc) the rest followed naturally or did you hit a wall at any point in your higher classes like OS'es and Compilers? Thanks for the input!

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  • why IEEE floating point number calculate exponent using a biased form?

    - by lenatis
    let's say, for the float type in c, according to the IEEE floating point specification, there are 8-bit used for the fraction filed, and it is calculated as first taken these 8-bit and translated it into an unsigned number, and then minus the BIASE, which is 2^7 - 1 = 127, and the result is an exponent ranges from -127 to 128, inclusive. But why can't we just treat these 8-bit pattern as a signed number, since the resulting range is [-128,127], which is almost the same as the previous one.

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  • P implies Q, how to read in english

    - by user177883
    how to read P implies Q in classical logic? example : Distributivity: Ka(X->Y) -> (KaX -> KaY) This is model logic which uses classical logic rules. KaX : a knows the that X is true. I m curious about how to read implication in english? if then else?

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  • Can a variable like 'int' be considered a primitive/fundamental data structure?

    - by Ravi Gupta
    A rough definition of a data structure is that it allows you to store data and apply a set of operations on that data while preserving consistency of data before and after the operation. However some people insist that a primitive variable like 'int' can also be considered as a data structure. I get that part where it allows you to store data but I guess the operation part is missing. Primitive variables don't have operations attached to them. So I feel that unless you have a set of operations defined and attached to it you cannot call it a data structure. 'int' doesn't have any operation attached to it, it can be operated upon with a set of generic operators. Please advise if I got something wrong here.

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  • A Computer Poem for those over 30 [closed]

    - by arvind
    I recd. a very good poem, that i wished to share with everyone. so for once we need no answers. lol ;-) A computer was something on TV From a science fiction show of note A window was something you hated to clean And ram was the cousin of a goat. Meg was the name of my girlfriend And gig was a job for the nights Now they all mean different things And that really mega bytes. An application was for employment A program was a TV show A cursor used profanity A keyboard was a piano.

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  • Count the number of objects in an Image

    - by kunjaan
    I am investigating the possibility of image processing to identify certain objects and also count them in an image. I will be given a picture and I need to identify the number of boxes present in that image. Does anybody have any experience with any Machine Vision/ Image Processing libraries like ImageJ, Fiji, JAI, jMagick ,Java Vision Toolkit? Which do you think is best suited for the job? What do you guys suggest? If the APIs can be used from Java, it would be better. Thank you. Edit: I am dealing with warehouse brown boxes. Yes I am talking about regular photos. The source is usually a mobile phone picture.

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  • Beginner Question ; About Prime Generation in "C" - What is wrong with my code ? -

    - by alorsoncode
    I'm a third year irregular CS student and ,i just realized that i have to start coding. I passed my coding classes with lower bound grades so that i haven't a good background in coding&programming. I'm trying to write a code that generates prime numbers between given upper and lower bounds. Not knowing C well, enforce me to write a rough code then go over it to solve. I can easily set up the logic for intended function but i probably create a wrong algorithm through several different ways. Here I share my last code, i intend to calculate that when a number gives remainder Zero , it should be it self and 1 , so that count==2; What is wrong with my implementation and with my solution generating style? I hope you will warm me up to programming world, i couldn't find enough motivation and courage to get deep into programming. Thanks in Advance :) Stdio and Math.h is Included int primegen(int down,int up) { int divisor,candidate,count=0,k; for(candidate=down;candidate<=up;candidate++) { for(divisor=1;divisor<=candidate;divisor++) { k=(candidate%divisor); } if (k==0) count++; if(count==2) { printf("%d\n", candidate); count=0; } else { continue; } } } int main() { primegen(3,15); return 0; }

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  • Why call-by-value evaluation strategy is not Turing complete?

    - by Roman
    I'm reading an article about different evaluation strategies (I linked article in wiki, but I'm reading another one not in English). And it says that unlike to call-by-name and call-by-need strategies, call-by-value strategy is not Turing complete. Can anybody explain, please, why is it so? If it's possible, add an example pls.

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  • wrap all lines that are longer than line length

    - by user1919840
    I am writing a program that limits each line to a certain length. this is what i got so far, i am almost done but i still need to cut each line, but i cant figure it out. def main(): filename = input("Please enter the name of the file to be used: ") openFile = open(filename, 'r+') file = openFile.read() lLength = int(input("enter a number between 10 & 20: ")) while (lLength < 10) or (lLength > 20) : print("Invalid input, please try again...") lLength = int(input("enter a number between 10 & 20: ")) wr = textwrap.TextWrapper() wraped = wr.wrap(file) print("Here is your output formated to a max of", lLength, "characters per line: ") wr.width = lLength wr.expand_tabs = True for lines in wraped: print(lines) an example of what the output SHOULD be is this. If the file specified contains this text: hgytuinghdt #here the length is 11 ughtnjuiknshfyth #here the length is 16 nmjhkaiolgytuhngjuin #here the length is 20 and the lLength is specified to 15 then this should print out: hgytuinghdt ughtnjuiknshfyt h nmjhkaiolgytuhng juin Thanks.

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  • How do I set advanced file associations in Windows 7?

    - by Dan O
    It used to be in Windows XP that I could make Warcraft III files load automatically into the game by double clicking on them. This association was made by going to file associations ADVANCED area and using this line: "C:\Program Files\Warcraft III\War3.exe" -loadfile "%1" Note that it takes an argument and an option. However, in Windows 7, the "Default Programs" "Set Associations" area doesn't seem to have this advanced area. Can I still get these files to open automatically?

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  • Remote desktop logs in with saved credentials when connecting from one computer but asks for username and password from another.

    - by AndrejaKo
    I have two computers on which I recently installed windows 7 64 bit. Using VPN, they connect to remote network on which there is a Windows Server 2000 SP4 computer. User is supposed to connect to server using remote desktop. I set same VPN and remote desktop settings on both computers with Windows 7. I set Remote desktop to save connection credentials on both computers, but when I connect to server form one computer, it uses saved credentials and I don't get log-in prompt on server side. On the other computer with same settings using same username and password, I get log-in prompt once the remote desktop connects to server. I even tried copying the .rdp file from the computer on which everything is working fine to the other computer, but that didn't help. Note that I'm not trying to have both computers connected at the same time. What is causing this and how do I make the other computer skip windows server 2000 log-in prompt.

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  • Why doesn't my Droid phone charge when connected to a powered USB hub that is not connected to my computer?

    - by pkaeding
    I notice that my new Motorola Droid phone charges perfectly fine when I connect it to my computer via the USB cable, or if I connect it to a car cigarette lighter-USB adapter, or a wall power-USB adapter. It also works fine when I connect it to a powered USB hub that is connected to my computer. However, if that same powered USB hub is not connected to my computer when I connect the phone, it does not charge. If I connect the computer to the hub, and then connect the phone to the hub, it will charge. If I then disconnect the computer from the hub, the phone will continue to charge. Does anyone know why this is happening, or what I can do to be able to charge my phone from a powered hub, without my computer being present?

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