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• System.Threading.Tasks - Limit the number of concurrent Tasks

  - by James

  I have just started to look at the new "System.Threading.Tasks" goodness in .Net 4.0, and would like to know if there is any build in support for limiting the number of concurrent tasks that run at once, or if this should be manually handled. E.G: If I need to call a calculation method 100 times, is there a way to set up 100 Tasks, but have only 5 execute simultaneously? The answer may just be to create 5 tasks, call Task.WaitAny, and create a new Task as each previous one finishes. I just want to make sure I am not missing a trick if there is a better way to do this. Thanks for any help.

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• Implementing PageRank using MapReduce

  - by Nick D.

  Hello, I'm trying to get my head around an issue with the theory of implementing the PageRank with MapReduce. I have the following simple scenario with three nodes: A B C. The adjacency matrix is here: A { B, C } B { A } The PageRank for B for example is equal to: (1-d)/N + d ( PR(A) / C(A) ) N = number of incoming links to B PR(A) = PageRank of incoming link A C(A) = number of outgoing links from page A I am fine with all the schematics and how the mapper and reducer would work but I cannot get my head around how at the time of calculation by the reducer, C(A) would be known. How will the reducer, when calculating the PageRank of B by aggregating the incoming links to B will know the number of outgoing links from each page. Does this require a lookup in some external data source?

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• When is calculating or variable-reading faster?

  - by Andreas Hornig

  hi, to be honest, I don't really know what the "small green men" in my cpu and compiler do, so I sometimes would like to know :). Currently I would like to know what's faster, so that I can design my code in a more efficient way. So for example I want to calclate something at different points in my sourcecode, when will it be faster to calculate it once and store it in a variable that's read and used for the next points it's needed and when is it faster to calculate it everytime? I think it's depending on how "complex" and "long" the calculation is and how fast then cache is, where variables are stored, but I don't have any clue what's faster :). Thanks for any reply to my tiny but important question! Andreas PS: perhaps it's important to know that I code in JAVA, but it's more a genral question.

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• How can I exceed the 60% Memory Limit of IIS7 in ASP.NET Caching application

  - by evilknot

  Pardon if this is more serverfault vs. stackoverflow. It seems to be on the border. We have an application that caches a large amount of product data for an e-commerce application using ASP.NET caching. This is a dictionary object with 65K elements, and our calculations put the object's size at ~10GB. Problem: The amount of memory the object consumes seems to be far in excess of our 10GB calculation. BIGGEST CONCERN: We can't seem to use over 60% of the 32GB in the server. What we've tried so far: In machine.config/system.web (sf doesn't allow the tags, pardon the formatting): processModel autoConfig="true" memoryLimit="80" In web.config/system.web/caching/cache (sf doesn't allow the tags, pardon the formatting): privateBytesLimit = "20000000000" (and 0, the default of course) percentagePhysicalMemoryUsedLimit = "90" Environment: Windows 2008R2 x64 32GB RAM IIS7 Nothing seems to allow us to exceed the 60% value. See screenshot of taskman. http://www.freeimagehosting.net/image.php?7a42144e03.jpg

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• exe files and Python

  - by Sorush Rabiee

  i have some questions about python: 1- How to build .exe files from .py files? 2- How to run a program with arguments and receive the result by python code? 3- How to load .NET library in python code (or write python in VS.NET IDE [!?])? 4- is built-in integer of python 3.1 something like a string? it calculates 200! in less than one second and calculates 2^1 to 2^7036 (by a simple recursive algorithm & writing them to a text file) with a 1.75GHz cpu in 4 minuets, so if it is a string, how it can be so fast like this? is there a great difference between memory type and logical calculation of python with c++? 5- what is the best python practice? how can i be an expert?

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• How to calculate bandwidth consumption for a Hosting Account using C# in ASP.Net Application?

  - by Steve Johnson

  HI all, I am working on SaaS Hosting Software. a large number of sites are hosted on the server. I am trying to calculate bandwidth consumption, (bytes transferred in and out) using C#, described Here using the MS Log Parser. In the above case, if the log files are deleted by the user or any administrator even, the bandwidth calculation will not be possible. Q1: *What is the standard way to measure the Bandwidth for various Hosting accounts (of websites) on a single server?* Q2: *If Log parser mechanism (as described above) is used, then how to take care of the security issue? Is there some system directory or event viewer logs or something which cannot be deleted except by the System account and contains bandwidth data?* Please point me in the right direction. Thanks

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• SQL 2003 Distance Latitude Longitude

  - by J.Hendrix

  I have a table full of Dealers along with their latitude and longitude. I am trying to determine the top n closest dealers to any given lat and lon. I already have the function to calculate distance between locations, but I want to do as few calculations as possible (my table can contain many thousands of entries). Currently I have to calculate the distance for each entry then sort them. Is there any way to sort before I do the calculation to improve performance? This question is good, but I will not always know my range. Should I just pick an arbitrarily high range then refine my results? I am thankful for any help the community can offer. declare @Lat real declare @lon real Set @lat = 41.05 Set @lon = -73.53 SELECT top 10 MemberID, Address1, City, State, Zip, Phone, Lat, Lon, (SELECT fun_DistanceLatLon] (@Lat,@lon,Lat,Lon)) as mDistance --Calculate distance FROM Dealers Order by (SELECT fun_DistanceLatLon] (@Lat,@lon,Lat,Lon))

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• java jama array problem

  - by agazerboy

  Hi All, I asked a question before but duffymo said it is not clear so i am going to post it again here. I am using Jama api for SVD calculation. I know very well about jama and SVD. Jama does not work if your column are more than rows. I have this situation. What should I do?? any help? I can't transpose the matrix too as it can produce wrong results. Thanks. P.S: I am calculating LSI with the help of jama. I am going like column(docs) and rows ( terms )

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• Scipy sparse... arrays?

  - by spitzanator

  Hey, folks. So, I'm doing some Kmeans classification using numpy arrays that are quite sparse-- lots and lots of zeroes. I figured that I'd use scipy's 'sparse' package to reduce the storage overhead, but I'm a little confused about how to create arrays, not matrices. I've gone through this tutorial on how to create sparse matrices: http://www.scipy.org/SciPy_Tutorial#head-c60163f2fd2bab79edd94be43682414f18b90df7 To mimic an array, I just create a 1xN matrix, but as you may guess, Asp.dot(Bsp) doesn't quite work because you can't multiply two 1xN matrices. I'd have to transpose each array to Nx1, and that's pretty lame, since I'd be doing it for every dot-product calculation. Next up, I tried to create an NxN matrix where column 1 == row 1 (such that you can multiply two matrices and just take the top-left corner as the dot product), but that turned out to be really inefficient. I'd love to use scipy's sparse package as a magic replacement for numpy's array(), but as yet, I'm not really sure what to do. Any advice? Thank you very much!

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• How to make a secure game in javascript ?

  - by rnaud

  Hello, I'm working on games using javascript some html and css, and I was wondering if there was any way to secure the game so that the user can't just call game.php?result=victory to finish the game and earn some point. As of right now here are the solution I have. For a chance game, start the page with the result already in place, win or loose, then just do some animations to show it, but all the score and win/loose stuff is done server-side. For a battle game, just get the action from the javascript call, and do the damage calculation, reaction of the oponent on the server and just send back the data. but the last solution imply that I will have to send actions each time the user do anything. This might work for a turn by turn battle game, but I think it would be to slow for any other kind of game. So my question is, is there some kind of secure way I can prep my javascript to secure the infomation sent.

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• Calculating string sizes on iPhone on a background thread

  - by jbrennan

  I've got some somewhat hefty string size calculations happening in my app (each one takes close to 500ms, and happens when the user scrolls to a new "page" in my app (like the Weather app). The delay only happens once per page, as the calculation only needs to be run once (and can even be cached for subsequent launches with the same data). Anyway, I still like to not block the UI for this type of work, as to me it screams using threads, but I know UIKit is not meant to be used from other threads. (I know NSString is not part of UIKit, but the string sizing methods are part of the UIKitAdditions...) So how should I go about doing this? What's the best way to not block the UI and do so safely?

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• 16 bit processor , memory addressing and memory cells

  - by Zia ur Rahman

  Suppose the accumulater register of the processor is of 16 bit , now we can call this processor as 16 bit processor, that is this processor supports 16 bit addressing. now my question is how we can calculate the number of memory cells that can be addressed by 16 bit addressing? according to my calculation 2 to the power 16 becomes 65055 it means the memory have 65055 cells now if we take 1KB=1000 Bytes then this becomes 65055/1000=65.055 now this means that 65 kilo bytes memory can be used with the processor having 16 bit addressing. now if we take 1KB=1024 Bytes then this becomes 65055/1024=63.5 ,it means that 63 kilo bytes memory can be used with this processor, but people say that 64 kilo bytes memory can be used. Now tell me am i right or wrong and why i am wrong why people say that 64kb memory can be used with the processor having 16 bit addressing?

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• BigDecimal serialization in GWT

  - by Domchi

  What is your preferred approach to serializing BigDecimal in GWT? Are there any clever workarounds, or do you simply use Double or String? Of all of the GWT pains this is so far the biggest; I'd hate to create two models, one for server and one for GWT, and transform data from one to the other. On the other hand, while I don't care much about using String instead of, say, javax.xml.datatype.Duration, I have to use BigDecimal on the server because of the calculations, which means either two models and conversion, or tons of tiny conversions to BigDecimal for every calculation.

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• Mix RGB colors (L*a*b*)

  - by Samuel

  Hello! Basically I want two mix two colours color1 and color2. Since simple calculation's bring up stuff like blue+yellow = grey ((color1.r + color2.r)/2 etc) i did some research and found that apparently mixing colors in order for the mixed color to look like we expect it too (e.g. blue+yellow = green) isn't that straight forward. What another stackoverflow post taught me was that in order two achieve the mixture correctly i'd have to use the L*a*b* space / CIELAB and linked to the wikipedia page about this topic. I found it informative but i couldn't really understand how to convert RGB to (sRGB and than to) L*a*b* - how to mix the obtained colors and how to convert back I hope somebody here can help me Thanks, Samuel

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• Explanation of casting/conversion int/double in C#

  - by cad

  I coded some calculation stuff (I copied below a really simplifed example of what I did) like CASE2 and got bad results. Refactored the code like CASE1 and worked fine. I know there is an implicit cast in CASE 2, but not sure of the full reason. Any one could explain me what´s exactly happening below? //CASE 1, result 5.5 double auxMedia = (5 + 6); auxMedia = auxMedia / 2; //CASE 2, result 5.0 double auxMedia1 = (5 + 6) / 2; //CASE 3, result 5.5 double auxMedia3 = (5.0 + 6.0) / 2.0; //CASE 4, result 5.5 double auxMedia4 = (5 + 6) / 2.0; My guess is that /2 in CASE2 is casting (5 + 6) to int and causing round of division to 5, then casted again to double and converted to 5.0. CASE3 and CASE 4 also fixes the problem.

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• Why is Java not telling me when I can't use Integer?

  - by Sebi

  For a small project (Problem 10 Project Euler) i tried to sum up all prime numbers below 2 millions. So I used a brute force method and iterated from 0 to 2'000'000 and checked if the number is a prime. If it is I added it to the sum: private int sum = 0; private void calculate() { for (int i = 0; i < 2000000; i++) { if (i.isPrime()) { sum = sum + i; } } sysout(sum) } The result of this calculation is 1179908154, but this is incorrect. So i changed int to BigInteger and now i get the correct sum 142913828922. Obviously the range of int was overflowed. But why can't Java tell my that? (e.g. by an exception)

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• Calling a method from within a django model save() override

  - by Jonathan

  I'm overriding a django model save() method. Within the override I'm calling another method of the same class and instance which calculates one of the instance's fields based on other fields of the same instance. class MyClass(models.Model): field1 = models.FloatField() field2 = models.FloatField() field3 = models.FloatField() def calculateField1(self) self.field1 = self.field2 + self.field3 def save(self, *args, **kwargs): self.calculateField1() super(MyClass, self).save(*args, **kwargs) The override method is called when I change the model in admin. Alas I've discovered that within calculateField1() field2 and field3 have the values of the instance from before I edited them in admin. If I enter the instance again in admin and save again, only then field1 receives the correct value as field2 and field3 are already updated. Is this the correct behavior on django's side? If yes, then how can I use the new values within calculateField1? I cannot implement the calculation within the save() as calculateField1() actually quite long and I need it to be called from elsewhere.

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• Most efficient way to check if a date falls between two dates?

  - by Dave Jarvis

  Given: Start Month & Start Day End Month & End Day Any Year What SQL statement results in TRUE if a date lands between the Start and End days? 1st example: Start Date = 11-22 End Date = 01-17 Year = 2009 Specific Date = 2010-01-14 TRUE 2nd example: Start Date = 11-22 End Date = 11-16 Year = 2009 Specific Date = 2010-11-20 FALSE 3rd example: Start Date = 02-25 End Date = 03-19 Year = 2004 Specific Date = 2004-02-29 TRUE I was thinking of using the MySQL functions datediff and sign plus a CASE condition to determine whether the year wraps, but it seems rather expensive. Am looking for a simple, efficient calculation. Update The problem is the end date cannot simply use the year. The year must be increased if the end month/day combination happens before the start date. The start date is easy: Start Date = date( concat_ws( '-', year, Start Month, Start Day ) The end date is not so simple. Thank you!

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• How to avoid the same calculations on column values over and over again in a select?

  - by Peter

  I sometimes write SELECTs on the form: SELECT a.col1+b.col2*c.col4 as calc_col1, a.col1+b.col2*c.col4 + xxx as calc_col1_PLUS_MORE FROM .... INNER JOIN ... ON a.col1+b.col2*c.col4 < d.some_threshold WHERE a.col1+b.col2*c.col4 > 0 When the calculations get rather involved and used up to 3-5 times within the same SELECT, I would really like to refactor that out in a function or similar in order to 1) hopefully improve performance / make use of cache 2) avoid forgetting to update one of the 4 calculations when I at a later stage realize I need to change the calculation. I usually have these selects within SPs. Any ideas?

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• Adjust SQL query to DB2

  - by Guy Roth

  Part of a complex query that our app is running contains the lines: ...(inner query) SELECT ... NULL as column_A, NULL as column_B, ... FROM ... This syntax of creating columns with null values is not allowed in DB2 altough it is totally OK in MSSQL and Oracle DBs. Technically I can change it to: '' as column_A, '' as column_B, But this doesn't have exactly the same meaning and can damage our calculation results. How can I create columns with null values in DB2 using other syntax??

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• AS3: How to access pixel data efficiently?

  - by JonoRR

  I'm working a game. The game requires entities to analyse an image and head towards pixels with specific properties (high red channel, etc.) I've looked into Pixel Bender, but this only seems useful for writing new colors to the image. At the moment, even at a low resolution (200x200) just one entity scanning the image slows to 1-2 Frames/second. I'm embedding the image and instance it as a Bitmap as a child of the stage. The 1-2 FPS situation is using BitmapData.getPixel() (on each pixel) with a distance calculation beforehand. I'm wondering if there's any way I can do this more efficiently... My first thought was some sort of spatial partioning coupled with splitting the image up into many smaller pieces. I also feel like Pixel Bender should be able to help somehow, however I've had little experience with it. Cheers for any help. Jonathan

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• Things to do with supercomputer.

  - by BigBoss

  HI, Guys I wanted to create SuperComputer out of my 3 old pcs soon. There are bunch of techniquies available on net for doing this and I will be using one of them. What I would like to get suggestion is what is next !! Many of them suggest some mathematical calculation or some graphic image rendering, which still is to me so boring and not inspiring at all. Please try to suggest something out of box. I would post results of it when I am done. Cheers !

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• Any way to do slanted/diagonal mouseovers via css/javascript?

  - by cksubs

  Hi, I have a box built via html borders. I want to connect the bottom left corner to the top right corner with a diagonal line. Either with html/css or by using a background image, doesn't matter. I'll figure that part out later. ------ - /- - / - - / - -/---- Here's the tricky part: I want a different thing to happen depending on which side of the line the mouse is hovering over. I'll do something like make some text visible or change the background color. Is that possible in web programing? I've thought of doing a "Riemann sum" type calculation with a bunch of invisible divs. Any easier way? Thanks!

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• Gradient a Parallelogram

  - by nuclearpenguin

  I'm working in JavaScript drawing on a canvas, and have four coordinates to draw a parallelogram, called A, B, C, and D starting from the top-left, top-right, bottom-left, and bottom right, respectively. An example of some coordinates might be: A: (3, 3) B: (4, 3) C: (1, 0) D: (2, 0) I can draw the parallelogram just fine, but I would like to fill it in with a gradient. I want the gradient to fill in from left to right, but matching the angle of the shape. The library I use (CAKE) requires a start and stop coordinate for the gradient. My stop and start would be somewhere half way between A and C, and end somewhere half way between B and D. Of course, it is not simply EXACTLY half way because the angles at A, B, C, and D are not right angles. So given this information (the coordinates), how to I find the point on the line A - C to start, and the point on the line B - D to stop? Remember, I'm doing this in JavaScript, so I have some good Math tools at my disposal for calculation.

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• Phantom updates due to decimal precision on calculated properties

  - by Jamie Ide

  This article describes my problem. I have several properties that are calculated. These are typed as decimal(9,2) in SQL Server and decimal in my C# classes. An example of the problem is: Object is loaded with a property value of 14.9 A calculation is performed and the property value is changed to 14.90393 When the session is flushed, NHibernate issues an update because the property is dirty Since the database field is decimal (9,2) the stored value doesn't change Basically a phantom update is issued every time this object is loaded. I don't want to truncate the calculations in my business objects because that tightly couples them to the database and I don't want to lose the precision in other calculations. I tried setting scale and precision or CustomType("Decimal(9,2)") in the mapping file but this appears to only affect schema generation. My only reasonable option appears to be creating an IUserType implementation to handle this. Is there a better solution?

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