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• Multiplying Block Matrices in Numpy

  - by Ada Xu

  Hi Everyone I am python newbie I have to implement lasso L1 regression for a class assignment. This involves solving a quadratic equation involving block matrices. minimize x^t * H * x + f^t * x where x 0 Where H is a 2 X 2 block matrix with each element being a k dimensional matrix and x and f being a 2 X 1 vectors each element being a k dimension vector. I was thinking of using nd arrays. such that np.shape(H) = (2, 2, k, k) np.shape(x) = (2, k) But I figured out that np.dot(X, H) doesn't work here. Is there an easy way to solve this problem? Thanks in advance.

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• Loading table sections when using headers

  - by Luis Tovar

  I cant seem to wrap my head around this. I have googled, and overstacked for hours now looking for examples that i can relate to. What I have is two arrays. The name of my first NSMutableArray is "showDates". I have 3 objects in here. Object 0: "Today, May 20th" Object 1: "Tomorrow, May 21st" Object 2: "Saturday, May 22nd" Then I have my second NSMutableArray named "showTimes" I have about 15 objects in there with strings in each object. ( i hope that makes sense? ) Each object is structured like this: Object 0: showID @"98022" eventID @"833" showTime @"1:30pm" showDate @"Today, May 20th" auditorium @"9" venue @"2991" Object 1: showID @"98222" eventID @"813" showTime @"2:30pm" showDate @"Tomorrow, May 21st" auditorium @"9" venue @"2991" Etc, etc, .... I have the headers working great in my tableView, but I cant seem to figure out how to add the objects in my "showTimes" array under the correct header. Any help would be greatly appreciated.

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• How does an interpreter switch scope?

  - by Dox

  I'm asking this because I'm relatively new to interpreter development and I wanted to know some basic concepts before reinventing the wheel. I thought of the values of all variables stored in an array which makes the current scope, upon entering a function the array is swapped and the original array put on some sort of stack. When leaving the function the top element of the "scope stack" is popped of and used again. Is this basically right? Isn't swapping arrays (which means moving around a lot of data) not very slow and therefore not used by modern interpreters?

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• Passing objects by reference or not in C#

  - by Piku

  Suppose I have a class like this: public class ThingManager { List<SomeClass> ItemList; public void AddToList (SomeClass Item) { ItemList.Add(Item); } public void ProcessListItems() { // go through list one item at a time, get item from list, // modify item according to class' purpose } } Assume "SomeClass" is a fairly large class containing methods and members that are quite complex (List<s and arrays, for example) and that there may be a large quantity of them, so not copying vast amounts of data around the program is important. Should the "AddToList" method have "ref" in it or not? And why? It's like trying to learn pointers in C all over again ;-) (which is probably why I am getting confused, I'm trying to relate these to pointers. In C it'd be "SomeClass *Item" and a list of "SomeClass *" variables)

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• Array in Bash Not Found

  - by Waffle

  I am trying to declare an array in bash, but when the code is run it says it cannot find the array. I have tried to write out the declaration of the array in several different ways, but it seems no matter how I try to declare it I cannot get it to work. I originally tried to declare it as such: candidate[1]= 0 candidate[2]= 0 candidate[3]= 0 The error messages that are returned are: votecalculation.sh: 13: candidate[1]=: not found votecalculation.sh: 14: candidate[2]=: not found votecalculation.sh: 15: candidate[3]=: not found After this I tried another solution I found online: ARRAY=( 'can1' 'can2' 'can3' ) When that is used it returns this error: votecalculation.sh: 12: Syntax error: "(" unexpected I am new to Bash and am getting really confused about arrays. Is there some specific way I need to declare an array or am I just going about it completely wrong?

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• Passing functions as arguements in Matlab

  - by Dave

  Hi, I'm trying to write a function that is gets two arrays and the name of another function as arguements. e.g. main.m: x=[0 0.2 0.4 0.6 0.8 1.0]; y=[0 0.2 0.4 0.6 0.8 1.0]; func2(x,y,'func2eq') func 2.m : function t =func2(x, y, z, 'func') //"unexpected matlab expression" error message here t= func(x,y,z); func2eq.m: function z= func2eq(x,y) z= x + sin(pi * x)* exp(y); Matlab tells gives me the above error message. I've never passed a function name as an arguement before. Where am I going wrong? p.s. sorry about the formatting of code above, I can't seems to get SO to show parts of the code as code.

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• How can I generate a list of words made up of combinations of three word lists in Perl?

  - by Chris Denman

  I have three lists of words. I would like to generate a single list of all the combinations of words from the three lists. List 1: red green blue List 2: one two List 3: apple banana The final list would like like so: red one apple red two apple red one banana red two banana ... and so on Ideally I'd like to pass in three arrays and the routine return one array. I have done a simple loop like so: foreach $word1 (@list1){ foreach $word2 (@list2){ foreach $word3 (@list3){ print "$word1 $word2 $word3\n"; } } } However, this doesn't work if there's nothing in the second or third list (I may only want to iterate between one, two or three lists at a time - in other words, if I only supply two lists it should iterate between those two lists).

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• Asp.net razor textbox array for list items

  - by yycdev

  I can't find or figure out how to take a list of items (cupcakes) and display them in razor with a quantity field. What is happening is I am not able to get the values for each cupcake quantity in the list. Can you do textbox arrays in Razor? VIEW <div class="form-group"> <label>Cupcakes</label> @foreach (var cupcake in Model.CupcakeList) { @Html.TextBox("CupcakeQuantities", cupcake.Id) @cupcake.Name <br/> } </div> MODEL public List<Cupcake> CupcakeList { get; set; } public List<int> CupcakeQuantities { get; set; } CONTROLLER public ActionResult Create() { var model = new PartyBookingModel() { CupcakeList = db.Cupcakes.ToList(), CupcakeQuantities = new List<int>() }; return View(model); }

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• n-grams from text in PostgreSQL

  - by harshsinghal

  I am looking to create n-grams from text column in PostgreSQL. I currently split(on white-space) data(sentences) in a text column to an array. select regexp_split_to_array(sentenceData,E'\s+') from tableName Once I have this array, how do I go about: Creating a loop to find n-grams, and write each to a row in another table Using unnest I can obtain all the elements of all the arrays on separate rows, and maybe I can then think of a way to get n-grams from a single column, but I'd loose the sentence boundaries which I wise to preserve. Sample SQL code for PostgreSQL to emulate the above scenario create table tableName(sentenceData text); INSERT INTO tableName(sentenceData) VALUES('This is a long sentence'); INSERT INTO tableName(sentenceData) VALUES('I am currently doing grammar, hitting this monster book btw!'); INSERT INTO tableName(sentenceData) VALUES('Just tonnes of grammar, problem is I bought it in TAIWAN, and so there aint any englihs, just chinese and japanese'); select regexp_split_to_array(sentenceData,E'\s+') from tableName; select unnest(regexp_split_to_array(sentenceData,E'\s+')) from tableName;

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• ASP.NET MVC submitting json array to controller as regular post request (nonajax)

  - by j3ko

  All the examples of json I can find online only show how to submit json arrays w/ the jquery command $.ajax(). I'm submitting some data from a custom user control as a json array. I was wondering if it's possible to submit a json array as a regular post request to the server (like a normal form) so the browser renders the page returned. Controller: [JsonFilter(Param = "record", JsonDataType = typeof(TitleViewModel))] public ActionResult SaveTitle(TitleViewModel record) { // save the title. return RedirectToAction("Index", new { titleId = tid }); } Javascript: function SaveTitle() { var titledata = GetData(); $.ajax({ url: "/Listing/SaveTitle", type: "POST", data: titledata, contentType: "application/json; charset=utf-8", }); } Which is called from a save button. Everything works fine but the browser stays on the page after submitting. I was thinking of returning some kind of custom xml from the server and do javascript redirect but it seems like a very hacky way of doing things. Any help would be greatly appreciated.

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• Custom "Very Long Int" Division Issue

  - by befall

  Hey everyone, So, for a very silly project in C++, we are making our own long integer class, called VLI (Very Long Int). The way it works (they backboned it, blame them for stupidity) is this: User inputs up to 50 digits, which are input as string. String is stored in pre-made Sequence class, which stores the string in an array, in reverse order. That means, when "1234" is input, it gets stored as [4|3|2|1]. So, my question is this: How can I go about doing division using only these arrays of chars? If the input answer is over 32 digits, I can't use ints to check for stuff, and they basically saying using long ints here is cheating. Any input is welcome, and I can give more clarification if need be, thanks everyone.

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• How to sort an array or ArrayList<Point> ASC first by x and then by y?

  - by newba

  Hi everyone, I just want to use Collections.sort or Arrays.sort to sort a list of points (class Point) by x first and then by y. I have a class Ponto that implements Comparable like this: public int compareTo(Ponto obj) { Ponto tmp = obj; if (this.x < tmp.x) { return -1; } else if (this.x > tmp.x) { return 1; } return 0; } but now I want to sort by y too after x. How can I do that by modifying the above code? Or is that a better and "clean" way to do this? I also use to pass this code to C++, in which I've created a structure called Point with a equivalent comparable method.

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• Glitch when moving camera in OpenGL

  - by CG

  I am writing a tile-based game engine for the iPhone and it works in general apart from the following glitch. Basically, the camera will always keep the player in the centre of the screen, and it moves to follow the player correctly and draws everything correctly when stationary. However whilst the player is moving, the tiles of the surface the player is walking on glitch as shown: Compared to the stationary (correct): Does anyone have any idea why this could be? Thanks for the responses so far. Floating point error was my first thought also and I tried slightly increasing the size of the tiles but this did not help. Changing glClearColor to red still leaves black gaps so maybe it isn't floating point error. Since the tiles in general will use different textures, I don't know if vertex arrays can be used (I always thought that the same texture had to be applied to everything in the array, correct me if I'm wrong), and I don't think VBO is available in OpenGL ES. Setting the filtering to nearest neighbour improved things but the glitch still happens every ten frames or so, and the pixelly result means that this solution is not viable anyway. The main difference between what I'm doing now and what I've done in the past is that this time I am moving the camera rather than the stationary objects in the world (i.e. the tiles, the player is still being moved). The code I'm using to move the camera is: void Camera::CentreAtPoint( GLfloat x, GLfloat y ) { glMatrixMode(GL_PROJECTION); glLoadIdentity(); glOrthof(x - size.x / 2.0f, x + size.x / 2.0f, y + size.y / 2.0f, y - size.y / 2.0f, 0.01f, 5.0f); glMatrixMode(GL_MODELVIEW); } Is there a problem with doing things this way and if so is there a solution?

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• ResultSet and aggregation

  - by kachanov

  Ok, I admit my situation is special There is a data system that supports SQL-92 and JDBC interface However the SQL requets are pretty expensive, and in my application I need to retreive the same data multiple times and aggregate it ("group by") on different fields to show different dimensions of the same data. For example on one screen I have three tables that show the same set or records but aggregated by City (1st grid), by Population (2nd grid), by number of babies (3rd grid) This amounts to 3 SQL queries (which is very slow), UNLESS anyone of you can suggest any idea any library from apache commons or from google code, so that I can select all records into ResultSet and get 3 arrays of data group by different fields from this single ResultSet. Am I'm missing some obvious and unexpected solution to this problem?

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• How do you store sets in Cassandra?

  - by Ben W

  I'd like to convert this JSON to a data model in Cassandra, where each of the arrays is a set with no duplicates: var data = { "data1": { "100": [1, 2, 3], "200": [3, 4] }, "data2": { "k1", [1], "k2", [4, 5] } } I'd like to query like this: data["data1"]["100"] to retrieve the sets. Anyone know how you might model this in Cassandra? (The only thing I came up with was columns whose name was a set value and the value of the column was an empty string, but that felt wrong.) It's not OK to serialize the sets as JSON or some other string, which would make this much easier. Also, I should note that it's OK to split data1 and data2 into separate ColumnFamilies, it's not necessary that they're keys in the same one.

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• Can't inherit from auto_str without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• Can't inherit from auto_ptr without problems

  - by fret

  What I want to do is this: #include <memory> class autostr : public std::auto_ptr<char> { public: autostr(char *a) : std::auto_ptr<char>(a) {} autostr(autostr &a) : std::auto_ptr<char>(a) {} // define a bunch of string utils here... }; autostr test(char a) { return autostr(new char(a)); } void main(int args, char **arg) { autostr asd = test('b'); return 0; } (I actually have a copy of the auto_ptr class that handles arrays as well, but the same error applies to the stl one) The compile error using GCC 4.3.0 is: main.cpp:152: error: no matching function for call to `autostr::autostr(autostr)' main.cpp:147: note: candidates are: autostr::autostr(autostr&) main.cpp:146: note: autostr::autostr(char*) I don't understand why it's not matching the autostr argument as a valid parameter to autostr(autostr&).

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• Can C++ do something like an ML case expression?

  - by Nathan Andrew Mullenax

  So, I've run into this sort of thing a few times in C++ where I'd really like to write something like case (a,b,c,d) of (true, true, _, _ ) => expr | (false, true, _, false) => expr | ... But in C++, I invariably end up with something like this: bool c11 = color1.count(e.first)>0; bool c21 = color2.count(e.first)>0; bool c12 = color1.count(e.second)>0; bool c22 = color2.count(e.second)>0; // no vertex in this edge is colored // requeue if( !(c11||c21||c12||c22) ) { edges.push(e); } // endpoints already same color // failure condition else if( (c11&&c12)||(c21&&c22) ) { results.push_back("NOT BICOLORABLE."); return true; } // nothing to do: nodes are already // colored and different from one another else if( (c11&&c22)||(c21&&c12) ) { } // first is c1, second is not set else if( c11 && !(c12||c22) ) { color2.insert( e.second ); } // first is c2, second is not set else if( c21 && !(c12||c22) ) { color1.insert( e.second ); } // first is not set, second is c1 else if( !(c11||c21) && c12 ) { color2.insert( e.first ); } // first is not set, second is c2 else if( !(c11||c21) && c22 ) { color1.insert( e.first ); } else { std::cout << "Something went wrong.\n"; } I'm wondering if there's any way to clean all of those if's and else's up, as it seems especially error prone. It would be even better if it were possible to get the compiler complain like SML does when a case expression (or statement in C++) isn't exhaustive. I realize this question is a bit vague. Maybe, in sum, how would one represent an exhaustive truth table with an arbitrary number of variables in C++ succinctly? Thanks in advance.

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• how to cast an array of char into a single integer number?

  - by SepiDev

  Hi guys, i'm trying to read contents of PNG file. As you may know, all data is written in a 4-byte manner in png files, both text and numbers. so if we have number 35234 it is save in this way: [1000][1001][1010][0010]. but sometimes numbers are shorter, so the first bytes are zero, and when I read the array and cast it from char* to integer I get wrong number. for example [0000] [0000] [0001] [1011] sometimes numbers are misinterpreted as negative numbers and simetimes as zero! let me give you an intuitive example: char s_num[4] = {120, 80, 40, 1}; int t_num = 0; t_num = int(s_num); => 3215279148 ?????? the result should be 241 but the output is 3215279148? I wish I could explain my problem well! how can i cast such arrays into a single integer value?

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• How to define a static array without a contant size in a constructor of a class? (C++)

  - by Keand64

  I have a class defined as: class Obj { public: int width, height; Obj(int w, int h); } and I need it to contain a static array like so: int presc[width][height]; however, I cannot define within the class, so it it possible to create a pointer to a 2D array (and, out of curiosity, 3, 4, and 5D arrays), have that as a member of the class, and intitalize it in the constructor like: int ar[5][6]; Obj o(5, 6, &ar); If that isn't possible, is there any way to get a static array without a contant size in a class, or am I going to have to use a dynamic array? (Something I don't want to do because I don't plan on ever changing the size of the array after it's created.)

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• How to store images efficiently (memory-wise) while still being able to process them

  - by Sheeo

  I'm working on a silverlight project where users get to create their own Collages. The problem When loading images into memory, I'm using BitmapImage so that they can be displayed directly with the Image control--but they're locked in afterwards. So I've tried storing them seperately aswell, but that just sucks up huge amounts of RAM. So in short, is there a class that'll let me store JPEG images, be able to show them with the image control, and still be able to export it afterwards? All this needs to be efficient--i.e. I'd rather not want any copying to ARGB arrays or use the WriteableBitmap to copy them over. I require to work with large collections of images, up to 300 at most. Any help apreciated!

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• OpenGL circle rotation

  - by user350632

  I'm using following code to draw my circles: double theta = 2 * 3.1415926 / num_segments; double c = Math.Cos(theta);//precalculate the sine and cosine double s = Math.Sin(theta); double t; double x = r;//we start at angle = 0 double y = 0; GL.glBegin(GL.GL_LINE_LOOP); for(int ii = 0; ii < num_segments; ii++) { float first = (float)(x * scaleX + cx) / xyFactor; float second = (float)(y * scaleY + cy) / xyFactor; GL.glVertex2f(first, second); // output Vertex //apply the rotation matrix t = x; x = c * x - s * y; y = s * t + c * y; } GL.glEnd(); The problem is that when scaleX is different from scaleY then circles are transformed in the right way except for the rotation. In my code sequence looks like this: circle.Scale(tmp_p.scaleX, tmp_p.scaleY); circle.Rotate(tmp_p.rotateAngle); My question is what other calculations should i perform for circle to rotate properly when scaleX and scaleY are not equal?

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• Send and receive Array as GET/POST using querystring

  - by Vanwaril

  I've got the following code, but it doesn't seem to work: var post_req = { array: [ [ { param1: 'something', param2: 123 } ], [ ], [ ], [ { param2: 'something', param4: 1234, param1: 'hello' } ] ] }; var data_send = querystring.stringify(post_req); var request = client.request('POST', '/', headers); request.end(data_send); and if( req.method == 'POST' ) { req.addListener('data', function(chunk) { POST = querystring.parse(chunk); console.log(POST); } } I end up with 5 sub-arrays, corresponding to the 5 parameters in the objects but with extra '][' characters in their names: { array: [ { '][param1': 'something' } , { '][param2': '123' } , { '][param2': 'something' } , { '][param4': '1234' } , { '][param1': 'hello' } ] }

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• Divide and Conquer Algo to find maximum difference between two ordered elements

  - by instance

  Given an array arr[] of integers, find out the difference between any two elements such that larger element appears after the smaller number in arr[]. Examples: If array is [2, 3, 10, 6, 4, 8, 1, 7] then returned value should be 8 (Diff between 10 and 2). If array is [ 7, 9, 5, 6, 3, 2 ] then returned value should be 2 (Diff between 7 and 9) My Algorithm: I thought of using D&C algorithm. Explanation 2, 3, 10, 6, 4, 8, 1, 7 then 2,3,10,6 and 4,8,1,7 then 2,3 and 10,6 and 4,8 and 1,7 then 2 and 3 10 and 6 4 and 8 1 and 7 Here as these elements will remain in same order, i will get the maximum difference, here it's 6. Now i will move back to merege these arrays and again find the difference between minimum of first block and maximum of second block and keep doing this till end. I am not able to implement this in my code. can anyone please provide a pseudo code for this?

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• ASP.NET C# Application Object Getters and Setters

  - by kellax

  I have had a hard time finiding a newbie friendly example of accessing Application Object. I have few things ( arrays ) i would like to store in Application Object to keep as persistant data for about 2h till AppRecycle Anyhow i know how to set an Application Object variable this way: // One way String[] users = new String[1000]; Application["users"] = users; // Another way Application.Add("users", users); However i do not know how to access these variables once in Application Object there is a Getter method Get however it requires int index and other one Contents which get's everything. Here i try to retrive my String[] array but gives me a error that i am trying to convert Object to String. String[] usersTable = Application["users"]; // Since this is an object i also tried Application.users but gives error

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