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• help with matlab and Discrete Fourier transform

  - by user504363

  Hi all I have previous experience with Matlab, but the problem that I face some problems in apply a problem in (DSP : Digital signal processing) which is not my study field, but I must finish that problems in days to complete my project. all i want is help me with method and steps of solving this problem in matlab and then I can write the code with myself. the problem is about the signal x(t) = exp(-a*t); 1) what's the Discrete Fourier transform of the sampled signal with sample rate fs 2) if a=1 and fs =1 , plot the amplitude spectrum of sampled signal 3) fix the sampling frequency at fs = 1(hz) [what's it mean ?] and plot the magnitude of the Fourier Transform of the sampled signal at various values of a thanks

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• Strategy in storing ad-hoc numbers/constants?

  - by Jiho Han

  I have a need to store a number of ad-hoc figures and constants for calculation. These numbers change periodically but they are different type of values. One might be a balance, a money amount, another might be an interest rate, and yet another might be a ratio of some kind. These numbers are then used in a calculation that involve other more structured figures. I'm not certain what the best way to store these in a relational DB is - that's the choice of storage for the app. One way, I've done before, is to create a very generic table that stores the values as text. I might store the data type along with it but the consumer knows what type it is so, in situations I didn't even need to store the data type. This kind of works fine but I am not very fond of the solution. Should I break down each of the numbers into specific categories and create tables that way? For example, create Rates table, and Balances table, etc.?

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• Where can an absolute beginner of Kohana PHP go to learn how to use it from the ground up?

  - by Sergio Tapia

  Hi guys! I have a month of free time and I've decided to launch my own website. It's going to be big and have dymanic content where different users with different roles can perform modifications to the site. Place comments, rate stores, list items, etc. This sound like a perfect opportunity for me to expand my horizons and learn a PHP Framework. I've used PHP bare bones before but nothing too complex. As of now, do you think Kohana is a mature framework to use? I've used Zend in the past for a course in Uni but it sucked horribly, I was new to the MVC model, but Zend had pretty much zero workable tutorials and guides for newbies. That's why I hated it. Where can I go to learn how to use Kohana from a retarded starting point? Thank you very much for your time.

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• Adding element to existing XML node

  - by Sathish

  Where am i going wrong??? I have an xml file with OppDetails as a tag already as shown below <OppDetails> <OMID>245414</OMID> <ClientName>Best Buy</ClientName> <OppName>International Rate Card</OppName> <CTALinkType>AO,IO,MC,TC</CTALinkType> </OppDetails> </OppFact> Now i am trying to add another element to it but getting an error in AppendChild method please help XmlNode rootNode = xmlDoc.SelectSingleNode("OppDetails"); XmlElement xmlEle = xmlDoc.CreateElement("CTAStartDate"); xmlEle.InnerText = ExcelUtility.GetCTAStartDate(); rootNode.AppendChild(xmlEle); xmlDoc.Save("C:\\test.xml");

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• How to schedule a cron job to backup a MySql database every week?

  - by KevinM

  What is a command line I can use to back up a MySql database every single week into a file name with the date (so that it doesn't collide with previous backups)? Also, is this a reasonable backup strategy? My database is relatively small (a complete export is only 3.2 megs right now). The churn rate is relatively low. I need to be able to get the complete DB back if something goes wrong. And it would be extra cool if there's a way that I could see the changes that occur across a time span.

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• How to render consistence and smooth moving animation on iphone / ipod / iphone simulator.

  - by shakthi

  I am trying render a simple animation(object movement animations) on iphone. I used opengl for object rendering. Movements appears to be smooth on the simulator. But if I used same code in the ipod, object movement is slower. In the iphone it is still slower. I googled a bit and found 'frame rate independent rendering method', which taught me the concept of 'time interval' and object movement based on it. However result is very unpleasant. There is a lot of jerk in the animation even when fps remains above 20. Following code fragment is used for calculation of time interval between successive frames and I am using that to move my animation. NSTimeInterval GetTimeIntervals(NSTimeInterval * inLastElapsedTime ) { NSTimeInterval intervalTime = 0; NSTimeInterval currentTime = [NSDate timeIntervalSinceReferenceDate]; if(*inLastElapsedTime != 0 ) { intervalTime = currentTime - *inLastElapsedTime; } *inLastElapsedTime = currentTime; return intervalTime; }

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• Best Asp.net Hosting

  - by dotnetguts

  There are many asp.net web hosting companies which spends lot on advertisement and also gives you very cheaper rate, as low as $5, but when it comes to support they are simply hopeless. Everyone can you please pass your experience with your past hosting companies and suggest any good asp.net hosting company? Please consider following requirement factors Asp.net 3.5 or 4.0 supported. Url Rewriter support GZip support (Dynamic through code) Initial Setup support (If required) SQL Server 2005 or 2008 Allow to access SQL Server DB using SQL Mgmt Studio Environment supporting Backup and Restore of DB on my own, without involving tech support team Full Text Search support FTP support I can able to send atleast 500 Emails daily. 99.9% Up Time (No matter all web hosting say they have 99.9% Up Time, but its not true). Alert Email to be sent when they do any maintenance or during downtime. Hosting Price should be reasonable. Incase you feel i am missing something please add to the list. Can anyone suggest good webhosting company based on above factors?

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• How to optimize an database suggestion engine

  - by Dimitar Vouldjeff

  Hi, I`m making an online engine for item-to-item recommending movies. I have made some researches and I think that the best way to implement that is using pearson correlation and make a table with item1, item2 and correlation fields, but the problem is that after each rate of item I have to regenerate the correlation for in the worst case N records (where N is the number of items). Another think that I read is the following article, but I haven`t thought a way to implement it. So what is your suggestion to optimize this process? Or any other suggestions? Thanks.

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• Database structure for ecommerce site

  - by imanc

  Hey Guys, I have been tasked with designing an ecommerce solution. The aspect that is causing me the most problems is the database. Currently the site consists of 10+ country based shops each with their own database (all residing on the same mysql instance). For the new site I'd rather all these shop databases be merged into one database so that all tables (products, orders, customers etc.) have a shop_id field. From a programming perspective this seems to make the most sense as we won't have to manage data across multiple databases. Currently the entire site generates about 120k orders a year, but is experiencing fairly heavy growth and we need to design a solution that will scale. In 5 years there may be more than a million orders per year and a database that contains 5 years order history (archiving maybe a solution here). The question is - do we use a single database, or do we keep the database-per-shop structure? I am currently trying to find supporting evidence for either avenue. The company I am designing the solution for prefer the per-shop database structure because they believe it will allow the sites to scale. But my argument is that the shop's database probably won't get that busy over the next few years that they exceed the capacity of a mysql database and a "no expenses spared" hardware set-up. I am wondering if anyone has any advice either way? Does anyone have experience with websites / ecommerce sites that have tables containing millions of records? I know there is probably not a clear answer here, but at what stage do we have too many records or too large table files to have a fast loading site? Also, if anyone has any advice on sources of information - books, websites, etc. where I can do further research, it would be highly appreciated! Cheers, imanc

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• Optimizing tiled maps in cocos2d-iphone

  - by Omega

  My cocos2d-iphone game has tiled maps. The tilesets textures are rather big. I got around 5 tilesets and each one is 2048x2048 (retina). My maps are around 80x80. They have around 8 layers and each one is obviously using one tileset. The frame rate falls (it goes around 30 sometimes. I know 30 is rather aceptable, but still, I want 50+). So given that textures are huge I can't afford to make many layers (since each one loads a texture of these). So how about I divide my tileset textures into much smaller tilesets (like 1024x1024 each)? That will allow me to use many more layers for my maps, right? Are there any other tips for huge retina display tile maps?

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• Where to draw the line between efficiency and practicality

  - by dclowd9901

  I understand very well the need for websites' front ends to be coded and compressed as much as possible, however, I feel like I have more lax standards than others when it comes to practical applications. For instance, while I understand why some would, I don't see anything wrong with putting selectors in the <html> or <body> tags on a website with an expected small visitation rate. I would only do this for a cheap website for a small client, because I can't really justify the cost of time otherwise. So, that said, do you think it's okay to draw a line? Where do you draw yours?

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• general things developer must know having 2+ years of exp?

  - by Salil

  Hi All, I have 2 years of experience in Ruby on Rails. I have basic knowledge (Very Basic) of mysql such as data insertion, join, select from more than one table. But now i want to know more about it cause my friends are having trouble in interview when ask questions like 1] What is the trigger. 2] which trigger call when 3] what's views in mysql? etc....... are this questions for developers?is it basic database? Also what other things developer should know having experience of 2 years or more. I am in double mind as i have over two years of exp. in ruby and i am learning new thing everyday in ruby only. if someone ask me to rate yourself i can't give more than 5 out of 10 in ROR only. So my question is What are the general things developer must know having 2+ years of exp? Regards, Salil Gaikwad

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• More efficient way to find & tar millions of files

  - by Stu Thompson

  I've got a job running on my server at the command line prompt for a two days now: find data/ -name filepattern-*2009* -exec tar uf 2008.tar {} ; It is taking forever, and then some. Yes, there are millions of files in the target directory. But just running... find data/ -name filepattern-*2009* -print > filesOfInterest.txt ...takes only two hours or so. At the rate my job is running, it won't be finished for a couple of weeks.. That seems unreasonable. Is there a more efficient to do this? Maybe with a more complicated bash script? A secondary questions is "why is my current approach so slow?"

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• Optimizing MySQL statement with lot of count(row) an sum(row+row2)...

  - by Zombies

  I need to use InnoDB storage engine on a table with about 1mil or so records in it at any given time. It has records being inserted to it at a very fast rate, which are then dropped within a few days, maybe a week. The ping table has about a million rows, whereas the website table only about 10,000. My statement is this: select url from website ws, ping pi where ws.idproxy = pi.idproxy and pi.entrytime > curdate() - 3 and contentping+tcpping is not null group by url having sum(contentping+tcpping)/(count(*)-count(errortype)) < 500 and count(*) > 3 and count(errortype)/count(*) < .15 order by sum(contentping+tcpping)/(count(*)-count(errortype)) asc; I added an index on entrytime, yet no dice. Can anyone throw me a bone as to what I should consider to look into for basic optimization of this query. The result set is only like 200 rows, so I'm not getting killed there.

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• SQL n:m Inheritance join

  - by Nightmares

  I want to join a table which contains n:m relationship between groups. (Groups are defined in a separate table). This table only has entries listing a member_group_id and a parent_group_id. Given this structure: id(int) | member_group_id(int) | parent_group_id(int) The "base" query looks like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id The "base" query correctly shows all relationships (I checked by doing it manually.) The problem is when I try to apply a where clause to this query to filter for a specific group as "point of origin" (the first group for which I want all parent groups) it returns only the closest parents. For example like this: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.member_group_id = p1.member_group_id where p1.group_id = 1 Can anyone give a clue how I can fix this? Or a different approach to realize this. (I suppose I could always do this in my C++ source code on the server side but I would have to transfer a entire table which has a high growth potential to the application server.) UPDATE: select p1.group_id, p2.group_id, p1.member_group_id, p2.member_group_id from group_member_group as p1 join group_member_group as p2 on p2.group_id = p1.member_group_id Typing mistake confirmed. Now I don't get past first level of inheritance period. Thanks at denied for pointing that out.

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• How to make a secure login using UDID or device token?

  - by Erik B

  So I'm making an app where I want the users to be able add, edit and rate content, but I do not want to force them to register. Instead I was planning on just using their device id or device token to identify them. I'm planning on making both an iPhone and Android version, so I'm looking for a general solution, but the iPhone version has higher priority, so an iPhone specific solution would also be welcome. The problem is that I don't want just anyone to be able to use my web service by sending a phony device id or someone else's device id. How would the client prove to the server that it is providing the correct device id?

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• Ruby: would using Fibers increase my DB insert throughput?

  - by Zombies

  Currently I am using Ruby 1.9.1 and the 'ruby-mysql' gem, which unlike the 'mysql' gem is written in ruby only. This is pretty slow actually, as it seems to insert at a rate of almost 1 per second (SLOOOOOWWWWWW). And I have a lot of inserts to make too, its pretty much what this script does ultamitely. I am using just 1 connection (since I am using just one thread). I am hoping to speed things up by creating a fiber that will create a new DB connection insert 1-3 records close the DB connection I would imagine launching 20-50 of these would greatly increase DB throughput. Am I correct to go along this route? I feel that this is the best option, as opposed to refactoring all of my DB code :(

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• OS X Dock API? Retrieve OS X active application's icon with badges and other modifications.

  - by pokstad

  Is there an API for retrieving the icons of the currently open apps on Mac OS X? I am trying to retrieve all the icons of the active applications along with any badges on top of the application (i.e. number of new messages in mail, or current download rate in Transmission). Is there some sort of Dock API? The only mention of an OSX API for retrieving information about currently active applications I have been able to find is the Process Manager API, which does not mention the ability to poll the dock or retrieve icon data.

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• Real time video stream from camera via server to Iphone

  - by devdevdev

  Hi I want to create an Iphone app that can display real time video from a camera. The intended setup is. Camera connected to Mac Mini delivering real time video to Iphone over local network. The Iphone doesn't need to display high quality or use a high frame rate, but it has to be real time. Max 1 sec delay. I've been searching a lot for a solution, but so far I have not found a resonable one. HTTP Live Stream is not a solution due to the delay. Any suggestions?

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• javascript disabling a div or a link? (for a 5-star rating system)

  - by Cyprus106

  Basically, I've created a 5-star rating system. Pretty typical. It shows how many stars other people have given the item, and then when a user hovers over the stars, it lights up x number of stars based on how many they're over. It's all run by AJAX. They click 5 stars it automatically adds their 5-star rating to the group. The problem is that after they rate it I want to turn the system off, but I can't seem to be able to do that. I've tried everything I can think of. I've tried using element.disable for the a hrefs and for the div, but it still lets them vote away, over and over again, at least in firefox.... Can anyone help me out with a method to simply "freeze" the stars on what the user voted?? If I need to add code that's cool! I figured it probably wasn't necessary in this situation!

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• PHP APC - Why is loading cached array op codes slow?

  - by Aaron Kreider

  I'm using APC to reduce my loading time for my PHP files. My files load very fast, except for one file where I define more than 100 arrays. This 270 kb file takes 200 ms to load. The rest of the files are full of objects, methods, and functions. I'm wondering: does OP code caching not work as well for arrays? My APC cache should be big enough to handle all of my classes. Currently 40% of my cache is free. My hit rate is 99%. apc.shm_size=32 M apc.max_file_size = 1M apc.shm_segments= 1 APC 3.1.6 I'm using PHP 5.2, Apache 2, and Windows Vista.

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• Mysql - Grouping the result based on a mathematical operation and SUM() function

  - by SpikETidE

  Hi all... I'm having the following two tables... Table : room_type type_id type_name no_of_rooms max_guests rate 1 Type 1 15 2 1254 2 Type 2 10 1 3025 Table : reservation reservation_id start_date end_date room_type booked_rooms 1 2010-04-12 2010-04-15 1 8 2 2010-04-12 2010-04-15 1 2 Now... I have this query SELECT type_id, type_name FROM room_type WHERE id NOT IN (SELECT room_type FROM reservation WHERE start_date >= '$start_date' AND end_date <= '$end_date') What the query does is it selects the rooms that are not booked between the start date and end date. Also, as you can see from the reservation table, we also have 'number of rooms booked between the two dates' factor also... I need to add this 'no.of booked rooms between the two dates' factor also in to the query... The query should return the type of rooms for which at least one room is free between the two dates. I worked out the logic but just can't represent it as a query....! How will you do this...? Thanks for your suggestions..!

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• Looking for a file database

  - by Mitchell Skurnik

  A few years ago there was a PHP script around called paFileDB. Essentially it created a database of files that end users could download and rate. It would keep track of the number of downloads as well. I am looking for a replacement of this coded in ASP.net C#. For the last week I have been searching around for "asp.net C# file database" and have just gotten how to upload files to a database. I have also search with some other terms. I do not need a full blown CMS like DotNetNuke or SharePoint. All I have been looking for is a system I could easily add to my existing .net C# site. I have thought about coding one myself, but with me being rather busy at work and this being a personal project, I simply do not have the time to code this myself. I hope that you guys can help. Thank you!

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• Have you dealt with space hardening?

  - by Tim Post

  I am very eager to study best practices when it comes to space hardening. For instance, I've read (though I can't find the article any longer) that some core parts of the Mars rovers did not use dynamic memory allocation, in fact it was forbidden. I've also read that old fashioned core memory may be preferable in space. I was looking at some of the projects associated with the Google Lunar Challenge and wondering what it would feel like to get code on the moon, or even just into space. I know that space hardened boards offer some sanity in such a harsh environment, however I'm wondering (as a C programmer) how I would need to adjust my thinking and code if I was writing something that would run in space? I think the next few years might show more growth in private space companies, I'd really like to at least be somewhat knowledgeable regarding best practices. Can anyone recommend some books, offer links to papers on the topic or (gasp) even a simulator that shows you what happens to a program if radiation, cold or heat bombards a board that sustained damage to its insulation? I think the goal is keeping humans inside of a space craft (as far as fixing or swapping stuff) and avoiding missions to fix things. Furthermore, if the board maintains some critical system, early warnings seem paramount.

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• What to do when you are a programmer and have a cold?

  - by Zak

  If you have a cold that isn't too bad, does it make sense to still go into the office and get some coding done? Assume a private office, no meetings for the day, and you have some documentation and coding tasks that need to get done. Also assume that you operate on a PTO system, where all days off are "vacation" or PTO. To clarify, should one just not code at all when under the weather? That's what I'm getting at. Will you just kick yourself in your own rear when you go back to deal with code you wrote when you are sick? What is the error defect rate of sick vs non-sick programming hours?

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