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  • FFT in MATLAB: wrong 0Hz frequency

    - by roujhan
    Hello I want to use fft in MATLAB to analize some exprimental data saved as an excell file. my code: A=xlsread('Book.xls'); G=A'; x=G(2, : ); N=length(x); F=[-N/2:N/2-1]/N; X = abs(fft(x-mean(x),N)) X = fftshift(X); plot(F,X) But it plots a graph with a large 0Hz wrong component, my true frequency is about 395Hz and it is not shown in the plotted graph. Please tell me what is wrong. Any help would be appreciated.

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  • Does the order of conditions in a WHERE clause affect MySQL performance?

    - by Greg
    Say that I have a long, expensive query, packed with conditions, searching a large number of rows. I also have one particular condition, like a company id, that will limit the number of rows that need to be searched considerably, narrowing it down to dozens from hundreds of thousands. Does make any difference to MySQL performance whether I do this: SELECT * FROM clients WHERE (firstname LIKE :foo OR lastname LIKE :foo OR phone LIKE :foo) AND (firstname LIKE :bar OR lastname LIKE :bar OR phone LIKE :bar) AND company = :ugh or this: SELECT * FROM clients WHERE company = :ugh AND (firstname LIKE :foo OR lastname LIKE :foo OR phone LIKE :foo) AND (firstname LIKE :bar OR lastname LIKE :bar OR phone LIKE :bar)

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  • How can I add floats together in different orders, and always get the same total?

    - by splicer
    Let's say I have three 32-bit floating point values, a, b, and c, such that (a + b) + c != a + (b + c). Is there summation algorithm, perhaps similar to Kahan summation, that guarantees that these values can be summed in any order and always arrive at the exact same (fairly accurate) total? I'm looking for the general case (i.e. not a solution that only deals with 3 numbers). Is arbitrary precision arithmetic the only way to go? I'm dealing with very large data sets, so I'd like to avoid the overhead of using arbitrary precision arithmetic if possible. Thanks!

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  • Mass data store with SQL SERVER

    - by Leo
    We need management 10,000 GPS devices, each GPS device upload a GPS data every 30 seconds, these data need to store in the database(MS SQL Server 2005). Each GPS device daily data quantity is: 24 * 60 * 2 = 2,880 10 000 10,000 GPS devices daily data quantity is: 10000 * 2880 = 28,800,000 Each GPS data approximately 160Byte, the amount of data per day is: 28,800,000 * 160 = 4.29GB We need hold at least 3 months of GPS data in the database, My question is: 1, whether SQL Server 2005 can support such a large amount of data store? 2, How to plan data table? (all GPS data storage in one table? Daily table? Each GPS device with a GPS data table?) The GPS data: GPSID varchar(21), RecvTime datetime, GPSTime datetime, IsValid bit, IsNavi bit, Lng float, Lat float, Alt float, Spd smallint, Head smallint, PulseValue bigint, Oil float, TSW1 bigint, TSW1Mask bigint, TSW2 bigint, TSW2Mask, BSW bigint, StateText varchar(200), PosText varchar(200), UploadType tinyint

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  • Deleting Part of An Array in Java to Free Memory on Heap

    - by kate
    I am implementing a dynamic programming algorithm for the knapsack problem in Java. I declare the array and then initialize its size to be [number of objects][capacity of knapsack]. When my number of objects or my capacity gets too large, I get a memory error because I run out of space on the heap. My questions is: If I delete rows from my double array as I go along, will Java free the memory as I delete? Or does Java reserve that memory space for the size of the array I originally created? If it's the latter, is there a way to manually free the memory in Java? Thanks for your Help!

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  • How to find (or generate) thousands of company names for test/demo purposes

    - by schefdev
    Ok, so this is rightfully a testing question more than a development question, but the two should go hand in hand :) So, I've got a system I'm building which includes business contact information. Pretty common no doubt. My test/demo database currently has randomly generated individual's names loaded (thanks to a handy IRS spreadsheet I found). This has worked great for internal testing and review purposes, but it looks really odd when shown to prospective customers. So.... Does anyone know where I can grab or find a listing of thousands of business names (address information too would be nice)? I've tried various online public information sources (e.g. EDGAR, and county based property records searches), but these all require me to manually stitch together the results in blocks of 50 names or so at a time. I could do this, but was really hoping for a search service or data store out there that had this type of information readily searchable and retrievable in very large batches. Thanks!

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  • Software to cd (change directories) into .jar/.ear files?

    - by Segphault
    Is there any software/script that will allow me to cd (change directories) into .jar/.ear/.zip files and edit the contents of the files it contains? I'm working on a large EJB project (yuck), and I frequently find myself in situations like the following: something.ear/ |-- something.jar/ | `-- fileINeedToEdit.xml I work primarily via the command line (Mac/Linux), so I find myself decompressing the files with jar -xvf, editing the file I need to edit, and then recompressing with jar -cvf. Obviously, this becomes a major headache after the first few times. I'd like to be able to treat the compressed files as directories, and simply cd (or some alternate command) to the file I want to edit. Does anyone know how I can accomplish this?

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  • Which are the current/emerging desktop development technologies worth looking into?

    - by heeboir
    Greetings, With all the existing development towards web development and emerging technologies in that area, I'm left wondering; what is a state of the art way to implement desktop applications in this day and age? If you were to start a new application of considerable size from scratch what technology would you invest your efforts in (focusing on cross platform portability, decent performance and interoperability with existing standards)? I've looked into the Adobe Air platform which appears quite impressive but seems rather limited to support a large application. Would something like Java/SWT still be the sensible choice? Do things like GWT fit the bill? Thanks P.S. I'm leaving my question a bit open-ended in an effort to gather diverse answers. Surely this a subjective matter and there is no right and wrong answer.

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  • Static initialization of a struct with class members

    - by JS Bangs
    I have a struct that's defined with a large number of vanilla char* pointers, but also an object member. When I try to statically initialize such a struct, I get a compiler error. typedef struct { const char* pszA; // ... snip ... const char* pszZ; SomeObject obj; } example_struct; // I only want to assign the first few members, the rest should be default example_struct ex = { "a", "b" }; SomeObject has a public default constructor with no arguments, so I didn't think this would be a problem. But when I try to compile this (using VS), I get the following error: error C2248: 'SomeObject::SomeObject' : cannot access private member declared in class 'SomeObject' Any idea why?

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  • Getting Popular Topics on a Custom Made Forum

    - by Navarr
    For this website we're working on, we're trying to get the most popular topics (based on how many posts have been made in them within the last 24 hours). We have a medium to large based forum, and the current MySQL query looks like this: SELECT `forums_topics`.*, ( SELECT COUNT(`id`) FROM `forums_posts` WHERE `postdate` > (UNIX_TIMESTAMP()-60*60*24) AND `topicid`=`forums_topics`.`id` ) AS `trendy_threads` FROM `forums_topics` WHERE `deleted`=0 ORDER BY `trendy_threads` DESC,`postdate` DESC LIMIT 3 This unfortunately causes an SQL timeout with just one query and Error 500's. How can we get this information as quickly and as efficiently as possible?

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  • Unresolved External Symbol

    - by TomO
    I am working on wrapping a large number of .h and .lib files from native C++ to Managed C++ for eventual use as a referenced .dll in C#. I have the .lib files linked in and everything has been going smoothly so far. Upon wrapping the latest .h file, I hit a snag when 2 functions came back with the link error: error LNK2019: unresolved external symbol __imp__htonl@4 referenced in function "public: void __thiscall Field::setCharacter(unsigned char,int)" (?setCharacter@Field@@QAEXEH@Z) myutils.lib I have referenced "myutils.lib" in the linker options, so that shouldn't be the issue. What's strange is that I have about 20 functions in this particular .h file and all of the rest are linking just fine except for 3 functions. Any ideas?

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  • symlink files newer than X age, then later remove symlink once file ages?

    - by bleomycin
    Hello everyone, i have a large number of files/folders coming in each day that are being sorted automatically to a wide variety of folders. I'm looking for a way to automatically find these files/folders and create symlinks to them all within an "incoming" folder. Searching for file age should be sufficient for finding the files, however searching for age and owner would be ideal. Then once the files/folders being linked to reach a certain age, say 5 days, remove the symlinks to them automatically from the "incoming" folder. Is this possible to do with a simple shell or python script that can be run with cron? Thanks!

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  • Is it bad practice to declare an array mid-function...

    - by Maximus
    In C, which would be more proper... void MyFunction() { int* array; int size; //do a bunch of stuff size = 10; array = (int*)(sizeof(int)*size); //do more stuff... //no longer need array... free(array); } Or is something like this okay? void MyFunction() { int size; //do a bunch of stuff size = 10; array[size]; //do more stuff... } The malloc uses the heap instead of the stack, so I suppose if you know size is going to be very large you'd want to malloc... but if you're quite certain size will be small enough, would the second method be reasonable?

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  • BlackBerry threading model

    - by Rory Fitzpatrick
    I've read a lot of comments mention in passing that the BlackBerry threading model deviates from the Java standard and can cause issues, but no amount of googling has enlightened me on what this means exactly. I've been developing a fairly large business application for the BlackBerry and, although I don't really have any previous experience with Java multi-threaded applications, haven't come across any issue that we've been able to blame on threading, other than what we caused ourselves. Can someone describe exactly how the BlackBerry threading model is different, and how I as a developer should take that into account? Obviously any links on the topic would also be great.

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  • Create a complex SQL query?

    - by mazzzzz
    Hey guys, I have a program that allows me to run queries against a large database. I have two tables that are important right now, Deposits and withdraws. Each contains a history of every user. I need to take each table, add up every deposit and withdraws (per user), then subtract the withdraws from the deposits. I then need to return every user whos result is negative (aka they withdrew more then they deposited). Is this possible in one query? Example: Deposit Table: |ID|UserName|Amount| |1 | Use1 |100.00| |2 | Use1 |50.00 | |3 | Use2 |25.00 | |4 | Use1 | 5.00 | WithDraw Table: |ID|UserName|Amount| |2 | Use2 | 5.00 | |1 | Use1 |100.00| |4 | Use1 | 5.00 | |3 | Use2 |25.00 | So then the result would output: |OverWithdrawers| | Use2 | Is this possible (I sure don't know how to do it)? Thanks for any help, Max

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  • using key/value collection in session

    - by jumpdart
    Question: What is a good datatype to keep in session for a large collection of keys and values to frequently reference and update? Application: Updating an old .NET web app with a million pages and grids to have all the grids maintain their sort. They currently access helper code to format themselves graphically on load and on sort. I figured I could add to that code to check for a key based on the page and grid id in a collection in session to see if it has a previous expression on load. and the on sort update/add its appropriate item in the collection. Thoughts? Dictionary vs NameValueCollection

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  • In Perl, can I limit the length of a line as I read it in from a file (like fgets)

    - by SB
    I'm trying to write a piece of code that reads a file line by line and stores each line, up to a certain amount of input data. I want to guard against the end-user being evil and putting something like a gig of data on one line in addition to guarding against sucking in an abnormally large file. Doing $str = <FILE> will still read in a whole line, and that could be very long and blow up my memory. fgets lets me do this by letting me specify a number of bytes to read during each call and essentially letting me split one long line into my max length. Is there a similar way to do this in perl? I saw something about sv_gets but am not sure how to use it (though I only did a cursory Google search). Thanks.

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  • Selecting data effectively sql

    - by learner135
    Hi, I have a very large table with over 1000 records and 200 columns. When I try to retreive records matching some criteria in the WHERE clause using SELECT statement it takes a lot of time. But most of the time I just want to select a single record that matches the criteria in the WHERE clause rather than all the records. I guess there should be a way to select just a single record and exit which would minimize the retrieval time. I tried ROWNUM=1 in the WHERE clause but it didn't really work cause I guess the engine still checks all the records even after finding the first record matching the WHERE criteria. Is there a way to optimize in case if I want to select just a few records? Thanks in advance. Edit: I am using oracle 10g.

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  • C++ converting hexadecimal md5 hash to decimal integer

    - by Zackery
    I'm doing Elgamal Signature Scheme and I need to use the decimal hash value from the message to compute S for signature generation. string hash = md5(message); cout << hash << endl; NTL::ZZ msgHash = strtol(hash.c_str(), NULL, 16); cout << msgHash << endl; There are no integer large enough to contain the value of 32 byte hexadecimal hash, and so I tried big integer from NTL library but it didn't work out because you cannot assign long integer to NTL::ZZ type. Is there any good solution to this? I'm doing this with visual C++ in Visual Studio 2013.

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  • Can you use POST to run a query in Solr (/select)

    - by RyanFetz
    I have queries that I am running against out solr index that sometimes have very long query parameters, I get errors when i run these queries, which i assume are do to the limit of a GET query parameters. Here is the method I use to query (JSON), this is to show I am using the Http Extensions (the client i use is a thin wrapper for HttpClient) not an end to end solution. 90% of the queries run fine, it is just when the params are large i get the 500 error from solr. I have read somewhere you can use POSt's when doing the select command but have not found examples of how to do it. Any help would be fantastic! public string GetJson(HttpQueryString qs) { using (var client = new DAC.US.Web.XmlHttpServiceClient(this.Uri)) { client.Client.DefaultHeaders.Authorization = new Microsoft.Http.Headers.Credential("Basic", DAC.US.Encryption.Hash.WebServiceCredintials); qs.Add("wt", "json"); if (!String.IsNullOrEmpty(this.Version)) qs.Add("version", this.Version); using (var response = client.Get(new Uri(@"select/", UriKind.Relative), qs)) { return response.Content.ReadAsString(); } } }

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  • SQLite: 2 Problems by working with table

    - by TianDong
    Hallo all, I have a SQliteDatabase object db, i want to create a table in db with the following code db.execSQL("CREATE TABLE IF NOT EXISTS "+ TABLE2_NAME + " (exer_nr INTEGER PRIMARY KEY ,exerText varchar(250),answerA varchar(250),answerB varchar(250),answerC varchar(250),answerD varchar(250))"); An Error occur. Why? Is this too large? How can i fix it? Another problem: I want to insert a row into the table, whose "exerText" column contains the following code as part of it's content. main( ) { int m=12, n=34; printf("%d%d", m+ +,+ +n); printf("%d%d\n",n+ +,+ +m); } An Error occur because of the "" and '' symbols in the code. How can i fix this problem ? Thanks a lot

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  • Where to find .NET version usage statistics?

    - by Mash
    There are some technologies like LINQ and WPF which are nice, but installation of .NET 3.5 is still slow procedure. It's important to understand - among Windows users how many of them have .NET 3.5 installed? Is there any good up to date stats gathered about .NET Version availability/usage? I've searched a lot, but can't find. Update: .NET version IS present in web-agent strings for FF and IE at least. So there SHOULD be somebody who have that information. Anyone with access to really large web-site logs? Update 2: I also understand Vista means that user have 3.5, but XP is still dominating the market.

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  • What does this C++ code mean

    - by Markus Orreilly
    I was trying to understand how webkit parses urls, and I'm having a hard time making heads or tails of this: Vector<char, 4096> buffer(fragmentEnd * 3 + 1); This line is on line 1214 (you can see it here: http://trac.webkit.org/browser/trunk/WebCore/platform/KURL.cpp#L1214). I get that it's making a vector of type char, with each entry being an array of char 4096 bytes large, but I don't get the buffer(fragmentEnd * 3 + 1) part. I think that it confuses me most b/c I can't find where the buffer variable is instantiated anywhere (shouldn't it be something more like Vector<char, 4096> buffer = new Vector<char, 4096>(...)? Thanks in advance

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  • Mvc3 IEnumerable<QuestionModel> have a List<QuestionOptionModel> property. When I post, I get null list

    - by user1649439
    There is a example here. I am trying to use this technique in a large form with a list(List) but when I post back, the Viewmodel.Order that should’ve contained list of items and activities return with the lists empty. My QuestionModel.cs like this. public int Id { get; set; } public string QuestionText { get; set; } public System.Nullable<bool> OptionType1 { get; set; } public System.Nullable<bool> OptionType2 { get; set; } public List<QuestionOptionModel> OptionList = new List<QuestionOptionModel>(); When I post back "IEnumerable questions" List OptionList comes null. How can I do this?

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  • are Hierarchical SIngletons in Java possible?

    - by Zach H
    I've been toying with an interesting idea (No idea if I'll include it in any code, but it's fun to think about) Let's say we have a program that requires a large number of classes, all of a certain subclass. And those classes all need to be singletons. Now, we could write the singleton pattern for each of those classes, but it seems wasteful to write the same code over and over, and we already have a common base class. It would be really nice to create a getSingleton method of A that when called from a subclass, returns a singleton of the B class (cast to class A for simplicity) class A{ public A getSingleton(){ //Wizardry } } class B extends A{ } A blargh = B.getSingleton() A gish = B.getSingleton() if(A == B) System.out.println("It works!") It seems to me that the way to do this would be to recognize and call B's default constructor (assuming we don't need to pass anything in.) I know a little of the black magic of reflection in Java, but i'm not sure if this can be done. Anyone interested in puzzling over this?

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