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• Who owes who money optimisation problem

  - by Francis

  Say you have n people, each who owe each other money. In general it should be possible to reduce the amount of transactions that need to take place. i.e. if X owes Y £4 and Y owes X £8, then Y only needs to pay X £4 (1 transaction instead of 2). This becomes harder when X owes Y, but Y owes Z who owes X as well. I can see that you can easily calculate one particular cycle. It helps for me when I think of it as a fully connected graph, with the nodes being the amount each person owes. Problem seems to be NP-complete, but what kind of optimisation algorithm could I make, nevertheless, to reduce the total amount of transactions? Doesn't have to be that efficient, as N is quite small for me.

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• Why would I want to have a non-standard attribute?

  - by dontWatchMyProfile

  The documentation on Core Data entities says: You might implement a custom class, for example, to provide custom accessor or validation methods, to use non-standard attributes, to specify dependent keys, to calculate derived values, or to implement any other custom logic. I stumbled over the non-standard attributes claim. It's just a guess: If my attribute is anything other than NSString, NSNumber or NSDate I will want to have a non-standard Attribute with special setter and getter methods? So, for example, if I wanted to store an image, this would be a non-standard Attribute with type NSData and a special method, say -(void)setImageWithFileURL:(NSURL*)url which then pulls the image data from the file, puts in in an NSData and assigns it to core data? Or did I get that wrong?

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• Draw text with in a rect with given width

  - by Forchita

  I'm trying to draw text on NSView subclass. I'm using an NSTextStorage, an NSLayoutManager, and an NSTextContainer. I followed Apple's doc and here's the method I use to calculate the necessary height for each text: NSSize newSize= NSMakeSize(width, 0.0); NSLayoutManager* layoutManager= [[textStorage layoutManagers] objectAtIndex:0]; NSTextContainer* textContainer= [[layoutManager textContainers] objectAtIndex:0]; [textContainer setContainerSize:newSize]; [textStorage addAttribute:NSFontAttributeName value:font range:NSMakeRange(0, [textStorage length])]; [textContainer setLineFragmentPadding:0.0]; [layoutManager glyphRangeForTextContainer:textContainer]; return [layoutManager usedRectForTextContainer:textContainer].size.height; The only problem is that I don't know how to draw in an NSRect with the layout manager. Can you help me please? Thanks in advance!

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• c++ design question: Can i query the base classes to find the number of derived classes satisfying a

  - by vivekeviv

  I have a piece of code like this class Base { public: Base(bool _active) { active = _active; } void Configure(); void Set Active(bool _active); private: bool active; }; class Derived1 : public Base { public: Derived1(bool active):Base(active){} }; similarly Derived 2 and Derived 3 Now if i call derived1Object.Configure, i need to check how many of the derived1Obj, derived2Obj,derived3Obj is active. Should i add this in the "Base" class like a function say, GetNumberOfActive()? And If the implementation is like this: class Imp { public: void Configure() { //Code instantiating a particular Derived1/2/3 Object int GetNumberOfActiveDerivedObj(); baseRef.Configure(int numberOfActiveDerivedClasses); } prive: Derived1 dObj1(true); Derived2 dObj2(false); Derived3 dObj3(true); }; should i calculate the numberOfActive Derived Objects in Imp Class? THanks

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• Find node level in a tree

  - by Álvaro G. Vicario

  I have a tree (nested categories) stored as follows: CREATE TABLE `category` ( `category_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `category_name` varchar(100) NOT NULL, `parent_id` int(10) unsigned DEFAULT NULL, PRIMARY KEY (`category_id`), UNIQUE KEY `category_name_UNIQUE` (`category_name`,`parent_id`), KEY `fk_category_category1` (`parent_id`,`category_id`), CONSTRAINT `fk_category_category1` FOREIGN KEY (`parent_id`) REFERENCES `category` (`category_id`) ON DELETE SET NULL ON UPDATE CASCADE ) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_spanish_ci I need to feed my client-side language (PHP) with node information (child+parent) so it can build the tree in memory. I can tweak my PHP code but I think the operation would be way simpler if I could just retrieve the rows in such an order that all parents come before their children. I could do that if I knew the level for each node: SELECT category_id, category_name, parent_id FROM category ORDER BY level -- No `level` column so far :( Can you think of a way (view, stored routine or whatever...) to calculate the node level? I guess it's okay if it's not real-time and I need to recalculate it on node modification.

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• Is there a transformation matrix that can scale the x and/or y axis logarithmically?

  - by Dave M

  I'm using .net WPF geometry classes to graph waveforms. I've been using the matrix transformations to convert from the screen coordinate space to my coordinate space for the waveform. Everything works great and it's really simple to keep track of my window and scaling, etc. I can even use the inverse transform to calculate the mouse position in terms of the coordinate space. I use the built in Scaling and Translation classes and then a custom matrix to do the y-axis flipping (there's not a prefab matrix for flipping). I want to be able to graph these waveforms on a log scale as well (either x axis or y axis or both), but I'm not sure if this is even possible to do with a matrix transformation. Does anyone know if this is possible, and if it is, what is the matrix?

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• Per Process Memory Calculation Alogrithm in Linux (say kernel 2.6 and above)

  - by Vaibhav Singh

  How do you calculate the linux process's Acutal Memory Usage and Not Virtual Memory Usage through the information supplied by /proc//smaps or maps or status or stat. To be more precise I need the heap usage only. I need to do this on an PowerPc based embedded system and hence I do not have utilities like exmap, valgrind etc. I understand the concepts of shared/non shared memory. I have read through the other topics given in this forum about the same but they talk more using the tools mentioned. What I need is the native way of calculation done by the same tools so that I may write a shell script for the same.

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• Structure of Astar (A*) graph search data in C#

  - by Shawn Mclean

  How do you structure you graphs/nodes in a graph search class? I'm basically creating a NavMesh and need to generate the nodes from 1 polygon to the other. The edge that joins both polygons will be the node. I'll then run A* on these Nodes to calculate the shortest path. I just need to know how to structure my classes and their properties? I know for sure I wont need to create a fully blown undirected graph with nodes and edges.

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• How to write a CASE WHEN statement with multiple DATEDIFF variables

  - by Anne C

  I need to calculate the difference between two dates (facility_start_date, facility_end_date) for a report in Reporting Services in SQL 2005. If the facility_end_date is null then it needs to use the report parameter @EndDate in the calculation. However if the facility_end_date is greater than the parameter @EndDate, then it also needs to use the paramenter @EndDate. The code below works fine except that if the facility_end_date is greater than the parameter @EndDate it is still calculating between the facility_start_date and facility_end_date, rather than between the facility_start_date and @EndDate. Any help would be appreciated. CASE WHEN facility_start_date > facility_end_date THEN NULL WHEN DATEPART(day , facility_start_date) > DATEPART(day , facility_end_date) THEN DATEDIFF(d , facility_start_date , ISNULL(facility_end_date , @EndDate)) - 1 WHEN DATEPART(day , .facility_end_date) > DATEPART(day , @EndDate) THEN DATEDIFF(d , facility_start_date , @EndDate) - 1 ELSE DATEDIFF(d , facility_start_date , ISNULL facility_end_date , @EndDate)) END

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• alternative to lag SQL command

  - by mahen

  I have a table which has a table like this. Month-----Book_Type-----sold_in_Dollars Jan----------A------------ 100 Jan----------B------------ 120 Feb----------A------------ 50 Mar----------A------------ 60 Mar----------B------------ 30 and so on I have to calculate the expected sales for each month and book type based on the last 2 months sales. So for March and type A it would be (100+50)/2 = 75 For March and type B it is 120/1 since no data for Feb is there. I was trying to use the lag function but it wouldn't work since there is data missing in a few rows. Any ideas on this?

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• Small questions on data structure

  - by John Graveston

  Hi, I'm trying to search the parent of a node with Kruskal's algorithm. My program works just fine, but I think I have heard of a method to improve the speed of the algorithm by reconstructing the tree while searching for the parent node and connecting it to the parent node. I'm pretty sure that I've heard of this somewhere, maybe in a lecture. Can anyone refresh my memory? And also, given a number of arrays, when searching for the minimum and the maximum value from a certain section of an array, what is the name of the tree that can calculate the minimum/maximum value from the array by making a binary tree that has the minimum/maximum value of each array in O(log N)?

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• Generating a perfectly distributed grid from array

  - by zath

  I'm looking for a formula or rule that will allow me to distribute n characters into a n*n grid with as perfect of a distribution as possible. Let's say we have an array of 5 characters, A through E. Here's an example of how it definitely shouldn't turn out: A B C D E B C D E A C D E A B D E A B C E A B C D The pattern is very clear here, it doesn't look "random". It would look better this way: A B C D E D E A B C B C D E A E A B C D C D E A B What I basically did here was place the A B C D E on the first row, then shift it by 2 on the second row, by 4 on the third row, 1 on the fourth row and 3 on the fifth row. Compared to the very bad example, this one shows no clear pattern. Though I'm certainly hoping there is a pattern, so I can use it to calculate not only small arrays such as this one, but arrays of any size. Any ideas as to how this can be accomplished?

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• wp e-commerce php modification

  - by user1015687

  Here are a few lines of code from a wordpress plugin (WP E-commerce) that calculate the price. Now what i want is that if 'cart_item' are more than 3 in quantity then the price should be (number of items * 4) else the function should work as it is listed below. Thnks for help. function calculate_subtotal($for_shipping = false) { 1047 global $wpdb; 1048 if($for_shipping == true ) { 1049 $total = 0; 1050 foreach($this->cart_items as $key => $cart_item) { 1051 if($cart_item->uses_shipping == 1) { 1052 $total += $cart_item->total_price; 1053 } 1054 } 1055 } else { 1056 $total = 0; 1057 if($this->subtotal == null) { 1058 foreach($this->cart_items as $key => $cart_item) { 1059 $total += $cart_item->total_price; 1060 } 1061 $this->subtotal = $total; 1062 } else { 1063 $total = $this->subtotal; 1064 } 1065 } 1066 return $total; 1067 }

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• Minimizing distance to a weighted grid

  - by Andrew Tomazos - Fathomling

  Lets suppose you have a 1000x1000 grid of positive integer weights W. We want to find the cell that minimizes the average weighted distance.to each cell. The brute force way to do this would be to loop over each candidate cell and calculate the distance: int best_x, best_y, best_dist; for x0 = 1:1000, for y0 = 1:1000, int total_dist = 0; for x1 = 1:1000, for y1 = 1:1000, total_dist += W[x1,y1] * sqrt((x0-x1)^2 + (y0-y1)^2); if (total_dist < best_dist) best_x = x0; best_y = y0; best_dist = total_dist; This takes ~10^12 operations, which is too long. Is there a way to do this in or near ~10^8 or so operations?

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• Shortest distance between points on a toroidally wrapped (x- and y- wrapping) map?

  - by mstksg

  I have a toroidal-ish Euclidean-ish map. That is the surface is a flat, Euclidean rectangle, but when a point moves to the right boundary, it will appear at the left boundary (at the same y value), given by x_new = x_old % width Basically, points are plotted based on: (x_new, y_new) = ( x_old % width, y_old % height) Think Pac Man -- walking off one edge of the screen will make you appear on the opposite edge. What's the best way to calculate the shortest distance between two points? The typical implementation suggests a large distance for points on opposite corners of the map, when in reality, the real wrapped distance is very close. The best way I can think of is calculating Classical Delta X and Wrapped Delta X, and Classical Delta Y and Wrapped Delta Y, and using the lower of each pair in the Sqrt(x^2+y^2) distance formula. But that would involve many checks, calculations, operations -- some that I feel might be unnecessary. Is there a better way?

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• Background position image overlay (Works in IE, not in Mozilla/Chrome/Safari)

  - by amm229

  Hi all, I am having an issue positioning a background image using the following jquery background position command in Firefox, Google Chrome, and Safari. The code works correctly in IE 8. $('#element).css({ backgroundPosition: 'xpx ypx' }); The x position of the image is calculated dynamically based on window size and the y position is static. The css appears to be modified correctly, however, the background image I am attempting to overlay is absent. See jscript code below: $(window).resize(function () { // image positioning variables var windowwidth = $(window).width(); var imgwidth = $('#imgFluid').width(); var offset = $('#divFluidBlur').offset(); // calculate and implement position blurPositionLeft = (windowwidth - imgwidth) - offset.left; $('#divFluidBlur').css({ backgroundPosition: blurPositionLeft + 'px' + ' 30px' }); // debug: display actual css Background Position of element to text box $("#txtActualBackgroundpos").val(document.getElementById ("divFluidBlur").style.backgroundPosition); Thanks in advance for your help, Andrew

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• [MS Access 2003 SQL] Switch is causing #error, why and how can I fix it...

  - by Chris

  I have 3 fields in my table: start, end (dates) and length (number, might be blank). My Aim is to calculate an end date using start and length where end doesn't exist... I have: SELECT Switch((g.length<>0) And IsDate(g.end),DateAdd("m",g.length,g.start)) AS field FROM table g If there is no start, end or length, Access displays blank - this is fine. If there is no end, but start and length are ok, the calculated date is shown - again fine. BUT If there is no end, or length, but a start exists, access displays #Error I don't understand why, and can't fix it, please help!

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• I need to send emails based on users input time and day (based on their time zone)? Kind of reminder

  - by evgelen

  I need to send emails based on users input time and day (based on their time zone)? Kind of reminder. For Example: User input 2:00pm Eastern Time on my server I have different time zone, how to calculate the time and send the email at users time-zone. Its a web application. What is the best way to accomplish it using asp.net c#? If somebody already done it in the past I will be glad to take a look at source code. Thank you for useful suggestions.

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• Calculating color shades

  - by matejv

  I have the next problem. I have a base color with couple of different shades of that color. Example: Base color: #4085c5 Shade: #005cb1 Now, I have a different color (let's say #d60620), but no shades of it. From the color I would like to calculate shades, that have similar difference as colors mentioned in first paragraph. First I tried calculating difference of RGB elements and applying them to second color, but the result was not like I expected to be. Than I tried with converting color to HSV, reading saturation value and applying the difference to second color, but again the resulting color was still weird. The formula was something like: (HSV(BaseColor)[S] - HSV(Shade)[S]) + HSV(SecondColor)[H] Does anyone know how this problem could be solved? I know I am doing something wrong, but I don't know what. :)

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• Timezone settings in MySQL - Using NOW()?

  - by matt74tm

  SOmewhat related to Doing calculations in MySQL vs PHP Right now, our database assumes that the system time is in UTC and uses that to calculate NOW(). PHP explicitly sets the timezone as UTC (so its impervious to server time zone shifts). An accidental shift of timezones on the server messed this relationship up at the database level and i'm now trying to figure out the ideal congiguration: configure Mysql to be in UTC, but also from the perspective that: our application may be on someone else's server where they might have a different TZ (so i cant set the timezone at the mysql/server level). How do i configure it at the specific database level?

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• Speedup C++ code

  - by Werner

  Hi, I am writing a C++ number crunching application, where the bottleneck is a function that has to calculate for double: template<class T> inline T sqr(const T& x){return x*x;} and another one that calculates Base dist2(const Point& p) const { return sqr(x-p.x) + sqr(y-p.y) + sqr(z-p.z); } These operations take 80% of the computation time. I wonder if you can suggest approaches to make it faster, even if there is some sort of accuracy loss Thanks

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• Will the next iPhone Simulator be able to simulate the high resolution of iPhone 4?

  - by dontWatchMyProfile

  As a follow-up to this question, the next one is: Will we be able to simulate our interfaces how they look on the new high resolution display, even without owning an iPhone 4? I guess that there is a formula that we can use to calculate the exact needed distance between our monitors and our eyes, to achieve the exact same visual effect of the Retina Display. This would help a lot to get things right. The first thing we need is an high resolution iPhone Simulator. I can't get any sleep until I know.

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• Creating non-framework calsses in CakePHP

  - by Affian

  I'm making a tournament manager in CakePHP 1.3 and I have a tournament controller which is fine but I want to implement a interface that can be used to define how a tournament runs. the controller needs to load a concrete class that implements the TournamentStyle interface that defines how the tournament works. At the end of a round the TournamentStyle is used to calculate the scores and winners and generate the next round of matches. That gives me a .php file for the interface and other files for the various styles. My question is: where would I put these files and how would I load them into my tournament controller?

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• SQL Server 2005 Reporting Services: How to count rows that are not null? Any hints for calculating t

  - by user329266

  Is there a way to count only records that are not null; similar to "COUNTA" in Excel? I would think this would be very simple process, but nothing I have tried has worked. If necessary, I can try to work this into my SQL query, but the query is already incredibly complicated. Also, I've found very little documentation for how to calculate report totals, and how to total from groups. Would anyone have any recommendations on what to use as a reference?

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• Help with getting data from resized image.

  - by nick

  I'm using an ASP.NET file upload control and then resizing an image and storing the new image in a new Bitmap. Here is the code I have so far: protected void ResizeImage() { Bitmap originalBMP = new Bitmap(FileUpload1.FileContent); //Calculate new image dimensions int origWidth = originalBMP.Width; int origHeight = originalBMP.Height; int sngRatio = origWidth / origHeight; int newWidth = 100; int newHeight = newWidth / sngRatio; Bitmap newBMP = new Bitmap(originalBMP, newWidth, newHeight); } I'm uploading directly to Amazon S3 and I need to pass some data to its upload method. How do I get the following information from my new bitmap that I have been using with the fileupload?: FileUpload1.FileBytes FileUpload1.FileBytes.Length Do I need to save my new bitmap to a stream so I can get an array of bytes?

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