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  • Tool to diagonalize large matrices

    - by Xodarap
    I want to compute a diffusion kernel, which involves taking exp(b*A) where A is a large matrix. In order to play with values of b, I'd like to diagonalize A (so that exp(A) runs quickly). My matrix is about 25k x 25k, but is very sparse - only about 60k values are non-zero. Matlab's "eigs" function runs of out memory, as does octave's "eig" and R's "eigen." Is there a tool to find the decomposition of large, sparse matrices? Dunno if this is relevant, but A is an adjacency matrix, so it's symmetric, and it is full rank.

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  • How to find largest common sub-tree in the given two binary search trees?

    - by Bhushan
    Two BSTs (Binary Search Trees) are given. How to find largest common sub-tree in the given two binary trees? EDIT 1: Here is what I have thought: Let, r1 = current node of 1st tree r2 = current node of 2nd tree There are some of the cases I think we need to consider: Case 1 : r1.data < r2.data 2 subproblems to solve: first, check r1 and r2.left second, check r1.right and r2 Case 2 : r1.data > r2.data 2 subproblems to solve: - first, check r1.left and r2 - second, check r1 and r2.right Case 3 : r1.data == r2.data Again, 2 cases to consider here: (a) current node is part of largest common BST compute common subtree size rooted at r1 and r2 (b)current node is NOT part of largest common BST 2 subproblems to solve: first, solve r1.left and r2.left second, solve r1.right and r2.right I can think of the cases we need to check, but I am not able to code it, as of now. And it is NOT a homework problem. Does it look like?

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  • Doing arithmetic with up to two decimal places in Python?

    - by user248237
    I have two floats in Python that I'd like to subtract, i.e. v1 = float(value1) v2 = float(value2) diff = v1 - v2 I want "diff" to be computed up to two decimal places, that is compute it using %.2f of v1 and %.2f of v2. How can I do this? I know how to print v1 and v2 up to two decimals, but not how to do arithmetic like that. The particular issue I am trying to avoid is this. Suppose that: v1 = 0.982769777778 v2 = 0.985980444444 diff = v1 - v2 and then I print to file the following: myfile.write("%.2f\t%.2f\t%.2f\n" %(v1, v2, diff)) then I will get the output: 0.98 0.99 0.00, suggesting that there's no difference between v1 and v2, even though the printed result suggests there's a 0.01 difference. How can I get around this? thanks.

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  • How does Hibernate detect dirty state of an entity object?

    - by ???'Lenik
    Is it using some kind of byte codes modification to the original classes? Or, maybe Hibernate get the dirty state by compare the given object with previously persisted version? I'm having a problem with hashCode() and equals() methods for complicated objects. I feel it would be very slow to compute hash code if the object has collection members, and cyclic references are also a problem. If Hibernate won't use hashCode()/equals() to check the dirty state, I guess I should not use equals()/hashCode() for the entity object (not value object), but I'm also afraid if the same operator (==) is not enough. So, the questions are: How does Hibernate know if a property of an object is changed? Do you suggest to override the hashCode()/equals() methods for complicated objects? What if they contains cyclic references? And, also, Would hashCode()/equals() with only the id field be enough?

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  • Get the last N rows in the database in order?

    - by Kristopher
    Let's say I have the following database table: record_id | record_date | record_value -----------+-------------+-------------- 1 | 2010-05-01 | 195.00 2 | 2010-07-01 | 185.00 3 | 2010-09-01 | 175.00 4 | 2010-05-01 | 189.00 5 | 2010-06-01 | 185.00 6 | 2010-07-01 | 180.00 7 | 2010-08-01 | 175.00 8 | 2010-09-01 | 170.00 9 | 2010-10-01 | 165.00 I want to grab the last 5 rows with the data ordered by record_date ASC. This is easy to do with: SELECT * FROM mytable ORDER BY record_date ASC LIMIT 5 OFFSET 4 Which would give me: record_id | record_date | record_value -----------+-------------+-------------- 6 | 2010-07-01 | 180.00 7 | 2010-08-01 | 175.00 3 | 2010-09-01 | 175.00 8 | 2010-09-01 | 170.00 9 | 2010-10-01 | 165.00 But how do I do this when I don't know how many records there are and can't compute the magic number of 4? I've tried this query, but if there are less than 5 records, it results in a negative OFFSET, which is invalid: SELECT * FROM mytable ORDER BY record_date ASC LIMIT 5 OFFSET (SELECT COUNT(*) FROM mytable) - 5; So how do I accomplish this?

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  • Determine the lat lngs of markers within a polygon

    - by subh
    I have a google maps app which plots markers as it loads. One of the new requirment is to to add a Polygon overlay encompassing a selection of markers by the user. I was able to achieve that using the Geometry Controls of the GMaps Utility Library Now, the next step is to form a group of the selected markers for which I would need to determine if the lat lngs of the markers falls within the lat lngs of the polygon? Is there a way to determine the lat lngs of a polygon and compute if the marker's lat lng is within its boundaries?

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  • Does Microsoft hate firefox? ASP.Net gridview performance in firefox bug?

    - by Maxim Gershkovich
    Could someone please explain the significant difference in speed between a firefox updatepanel async postback and one performed in IE? Average Firefox Postback Time For 500 objects: 1.183 Second Average IE Postback Time For 500 objects: 0.295 Seconds Using firebug I can see that the majority of this time in FireFox is spent on the server side. A total of 1.04 seconds. Given this fact the only thing I can assume is causing this problem is the way that ASP.Net renders its controls between the two browsers. Has anyone run into this problem before? VB.Net Code Protected Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Button1.Click GridView1.DataBind() End Sub Public Function GetStockList() As StockList Dim res As New StockList For l = 0 To 500 Dim x As New Stock With {.Description = "test", .ID = Guid.NewGuid} res.Add(x) Next Return res End Function Public Class Stock Private m_ID As Guid Private m_Description As String Public Sub New() End Sub Public Property ID() As Guid Get Return Me.m_ID End Get Set(ByVal value As Guid) Me.m_ID = value End Set End Property Public Property Description() As String Get Return Me.m_Description End Get Set(ByVal value As String) Me.m_Description = value End Set End Property End Class Public Class StockList Inherits List(Of Stock) End Class Markup <form id="form1" runat="server"> <asp:ScriptManager ID="ScriptManager1" runat="server"> </asp:ScriptManager> <script type="text/javascript" language="Javascript"> function timestamp_class(this_current_time, this_start_time, this_end_time, this_time_difference) { this.this_current_time = this_current_time; this.this_start_time = this_start_time; this.this_end_time = this_end_time; this.this_time_difference = this_time_difference; this.GetCurrentTime = GetCurrentTime; this.StartTiming = StartTiming; this.EndTiming = EndTiming; } //Get current time from date timestamp function GetCurrentTime() { var my_current_timestamp; my_current_timestamp = new Date(); //stamp current date & time return my_current_timestamp.getTime(); } //Stamp current time as start time and reset display textbox function StartTiming() { this.this_start_time = GetCurrentTime(); //stamp current time } //Stamp current time as stop time, compute elapsed time difference and display in textbox function EndTiming() { this.this_end_time = GetCurrentTime(); //stamp current time this.this_time_difference = (this.this_end_time - this.this_start_time) / 1000; //compute elapsed time return this.this_time_difference; } //--> </script> <script type="text/javascript" language="javascript"> var time_object = new timestamp_class(0, 0, 0, 0); //create new time object and initialize it Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(BeginRequestHandler); Sys.WebForms.PageRequestManager.getInstance().add_endRequest(EndRequestHandler); function BeginRequestHandler(sender, args) { var elem = args.get_postBackElement(); ActivateAlertDiv('visible', 'divAsyncRequestTimer', elem.value + ''); time_object.StartTiming(); } function EndRequestHandler(sender, args) { ActivateAlertDiv('visible', 'divAsyncRequestTimer', '(' + time_object.EndTiming() + ' Seconds)'); } function ActivateAlertDiv(visstring, elem, msg) { var adiv = $get(elem); adiv.style.visibility = visstring; adiv.innerHTML = msg; } </script> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <Triggers> <asp:AsyncPostBackTrigger ControlID="Button1" EventName="click" /> </Triggers> <ContentTemplate> <asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"> </asp:UpdateProgress> <asp:Button ID="Button1" runat="server" Text="Button" /> <div id="divAsyncRequestTimer" style="font-size:small;"> </div> <asp:GridView ID="GridView1" runat="server" DataSourceID="ObjectDataSource1" AutoGenerateColumns="False"> <Columns> <asp:BoundField DataField="ID" HeaderText="ID" SortExpression="ID" /> <asp:BoundField DataField="Description" HeaderText="Description" SortExpression="Description" /> </Columns> </asp:GridView> <asp:ObjectDataSource ID="ObjectDataSource1" runat="server" SelectMethod="GetStockList" TypeName="WebApplication1._Default"> </asp:ObjectDataSource> </ContentTemplate> </asp:UpdatePanel> </form>

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  • MATLAB: draw centroids

    - by Myx
    Hello - my main question is given a feature centroid, how can I draw it in MATLAB? In more detail, I have an NxNx3 image (an rgb image) of which I take 4x4 blocks and compute a 6-dimensional feature vector for each block. I store these feature vectors in an Mx6 matrix on which I run kmeans function and obtain the centroids in a kx6 matrix, where k is the number of clusters and 6 is the number of features for each block. How can I draw these center clusters in my image in order to visualize if the algorithm is performing the way I wish it to perform? Or if anyone has any other way/suggestions on how I can visualize the centroids on my image, I'd greatly appreciate it. Thank you.

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  • Preallocate memory for a program in Linux before it gets started

    - by Fyg
    Hi, folks, I have a program that repeatedly solves large systems of linear equations using cholesky decomposition. Characterising is that I sometimes need to store the complete factorisation which can exceed about 20 GB of memory. The factorisation happens inside a library that I call. Furthermore, this matrix and the resulting factorisation changes quite frequently and as such the memory requirements as well. I am not the only person to use this compute-node. Therefore, is there a way to start the program under Linux and preallocate free memory for the process? Something like: $: prealloc -m 25G ./program

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  • for loop will not loop

    - by Bjørn Jostein Aurheim
    I have a for loop that I will use to compute time intervals to add to an ArrayList. The problem is that I can not prove that the for loop is being executed. Nothing is printed when using the system.out.println() statement, and nothing is added to the array from inside the loop ... any sugestions? // lager tidspunkter og legger disse inn i en Array kalt tider tid.setTimer(16); tid.setMinutter(0); tid.setSekunder(0); tider.add(tid.asString());// String "16:00" is added as it should System.out.println("tiden er: "+tid.asString());// gives 16:00 printed for(int i=0;i>12;i++){ System.out.println("er i løkken");// gives nothing printed tid.increaseMinutter(30); System.out.println(tid.asString());// gives nothing printed tider.add(tid.asString()); }

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  • Adjusting for compass wrap around in a navigation application

    - by chris12892
    I have a application where I am guiding a vehicle on compass headings and I am having an issue when the vehicle is crossing from 360 degrees to 0 degrees. In this case, there are no smarts in the control loop to compute that the nearest way to turn to follow a heading. For example, if the vehicle is instructed to follow a heading of 360 degrees, it will inevitably drifts a few degrees to ether side. If it drifts over to 0+ degrees, the control loop will go nuts and try to steer the vehicle all the way around to get it to 360 degrees again. Is there a graceful way to deal with this? The way the navigate function is written, I use an external PID controller class and I calculate the heading like this: lock (steering) { if (!Engaged) { return; } double mv = 90 + Trim + pidController.CalculateCorrection(flyHeading, currentHeading); steering.Degree = mv; } Thanks!

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  • Measuring time taken to display an object in Flex

    - by dta
    For e.g. function showIt():void { something.visible = true; } function init():void { time1 = flash.utils.getTimer(); showIt(); time2 = flash.utils.getTimer(); } <mx:st id="something" visible="false"/> <mx:Button click="init()"/> In the above code, I want to measure the time taken to display st on screen. Is it enough to compute time2 - time1? Or should I put an event handler on render? Or some other way?

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  • java memory usage

    - by xdevel2000
    I know I always post a similar question about array memory usage but now I want post the question more specific. After I read this article: http://www.javamex.com/tutorials/memory/object_memory_usage.shtml I didn't understand some things: the size of a data type is always the same also on different platform (Linux / Windows 32 / 64 bit)??? so an int will be always 32 bit?; when I compute the memory usage I must put also the reference value itself? If I have an object to a class that has an int field its memory will be 12 (object header) + 4 reference + 4 (the int field) + 3 (padding) = 24 bytes??

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  • Efficient bitshifting an array of int?

    - by nn
    Hi, To be on the same page, let's assume sizeof(int)=4 and sizeof(long)=8. Given an array of integers, what would be an efficient method to bitshift the array to either the left or right? I am contemplating an auxiliary variable such as a long, that will compute the bitshift for the first pair of elements (index 0 and 1) and set the first element (0). Continuing in this fashion the bitshift for elements (index 1 and 2) will be computer, and then index 1 will be set. I think this is actually a fairly efficient method, but there are drawbacks. I cannot bitshift greater than 32 bits. I think using multiple auxiliary variables would work, but I'm envisioning recursion somewhere along the line.

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  • How can I intercept a Tomcat request at socket level?

    - by Miguel Pardal
    Hi, I'm doing a performance study for a web application framework running on Apache Tomcat 6. I'm trying to measure the time overhead of handling HTTP requests. What I would like to do is: / // just before first request byte is read long t1 = System.nanoTime(); // request is processed... // just after final byte is written to response long t2 = System.nanoTime(); / Then I would compute the total time (t2 - t1). Is there a way to do this? Thanks for your help!

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  • Drawing rectangles on a grid in a web browser

    - by Dhruv
    I would like to create an online, simple WYSIWYG drawing editor allowing people to draw rectangular shapes. I'm thinking of a grid which the lines and points can snap on to, ensuring that the lines are strictly vertical or horizontal. I will be parsing the rectangular shapes to obtain some area calculations and compute certain things. How can I achieve the drawing ability? The new canvas tag is good but people have been telling me that IE does not support it. I found some Java applets but I have never programmed in Java before. Is there a way to do this using pure javascript or jquery? Does ASP.NET help at all? Thanks.

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  • Windows azure deployment

    - by smoothe
    I just built a simple hello world windows azure service containing just one web role, I used visual studio 2008 and Windows azure tools for VS 1.2 I am pretty new to this and I have been trying to deploy an application all afternoon now. I'm in australia and deploying in the region Asia anywhere. I have pretty much followed the info provided on MSDN and it says uploaded 95% then after about ten minutes the deployment disappears. I have tried using the old windows azure developer portal and 30minutes later I can not access the service and it's status is either busy or stopped. I have the introductory offer for an extra small compute instance on the subscription I am deploying to. Can anyone with experience with windows azure elaborate on the subject of deploying apps and the status on my application, I am very keen to get into the platform and this issue has just about spoiled my weekend.

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  • How to order by results from 2 seperate tables in PHP and MySQL.

    - by Vafello
    I am trying to output results of 2 sql queries to one JSON file. The problem is that I would like to order them ascending by distance which is the result of equation that takes homelat and homelon from the users table and lat, lng from locations table.(basically it takes lattitude and longitude of one point and another and computes the distance between these points). Is it possible to take some parameters from both select queries, compute it and output the result in ascending order? $wynik = mysql_query("SELECT homelat, homelon FROM users WHERE guid='2'") or die(mysql_error()); ; $query = "SELECT * FROM locations WHERE timestamp"; $result = map_query($query); $points = array(); while ($aaa = mysql_fetch_assoc($wynik)) { while ($row = mysql_fetch_array($result, MYSQL_ASSOC)) { array_push($points, array('name'=>$row['name'], 'lat'=>$row['lat'], 'lng'=>$row['lng'], 'description'=>$row['description'], 'eventType'=>$row['eventType'], 'date'=>$row['date'], 'isotime'=>date('c', ($row['timestamp'])), 'homelat'=>$aaa['homelat'], 'homelon'=>$aaa['homelon'])); } echo json_encode(array("Locations"=>$points));

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  • Distance between hyperplanes

    - by michael dillard
    I'm trying to teach myself some machine learning, and have been using the MNIST database (http://yann.lecun.com/exdb/mnist/) do so. The author of that site wrote a paper in '98 on all different kinds of handwriting recognition techniques, available at http://yann.lecun.com/exdb/publis/pdf/lecun-98.pdf. The 10th method mentioned is a "Tangent Distance Classifier". The idea being that if you place each image in a (NxM)-dimensional vector space, you can compute the distance between two images as the distance between the hyperplanes formed by each where the hyperplane is given by taking the point, and rotating the image, rescaling the image, translating the image, etc. I can't figure out enough to fill in the missing details. I understand that most of these are indeed linear operators, so how does one use that fact to then create the hyperplane? And once we have a hyperplane, how do we take its distance with other hyperplanes?

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  • Create a date from Credit Card expire in MMYY format

    - by Sophtware
    I need to convert a credit card expire field from MMYY to a date field I can use in a MS SQL query so I can compute when credit cards are expiring in the future. Basically, I need to go from MMYY to MM/DD/YYYY, where the day part could just be '01' (the first of the month). I'm looking for credit cards that are expiring next month from a database. The problem I'm running into is when next month is the first month of the next year. Here's the code I have for determining expired card: (CAST(SUBSTRING(CCExpire,3,2) as int) + 2000 < YEAR(GETDATE())) or ( (CAST(SUBSTRING(CCExpire,3,2) as int) + 2000 = YEAR(GETDATE())) AND (CAST(SUBSTRING(CCExpire,1,2) as int) < MONTH(GETDATE())) ) And here's the code for cards expiring this month: (CAST(SUBSTRING(CCExpire,3,2) as int) + 2000 = YEAR(GETDATE())) AND (CAST(SUBSTRING(CCExpire,1,2) as int) = MONTH(GETDATE())) Now I need code for cards expiring next month...

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  • a nicer way to create structs in a loop

    - by sandra
    Hi guys, I haven't coded in C++ in ages. And recently, I'm trying to work on something involving structs. Like this typedef struct{ int x; int y; } Point; Then in a loop, I'm trying to create new structs and put pointers to them them in a list. Point* p; int i, j; while (condition){ // compute values for i and j with some function... p = new Point; p* = {i, j}; //initialize my struct. list.append(p); //append this pointer to my list. } Now, my question is it possible to simplify this? I mean, the pointer variable *p outside of the loop and calling p = new Point inside the loop. Isn't there a better/nicer syntax for this?

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  • Python 3: Most efficient way to create a [func(i) for i in range(N)] list comprehension

    - by mejiwa
    Say I have a function func(i) that creates an object for an integer i, and N is some nonnegative integer. Then what's the fastest way to create a list (not a range) equal to this list mylist = [func(i) for i in range(N)] without resorting to advanced methods like creating a function in C? My main concern with the above list comprehension is that I'm not sure if python knows beforehand the length of range(N) to preallocate mylist, and therefore has to incrementally reallocate the list. Is that the case or is python clever enough to allocate mylist to length N first and then compute it's elements? If not, what's the best way to create mylist? Maybe this? mylist = [None]*N for i in range(N): mylist[i] = func(i)

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  • Copy of Access mdb database being updated by live database

    - by James
    I'm trying to compute statistics for data held in an Access .mdb database. In order to avoid interfering with the live database, I'm working from a copy which I made by simply using copy-paste in Windows Explorer. The copy resides in the same directory, but with a different name. I'm using R and RODBC to connect to the copy of the file. The strange thing is that new data that is being updated on the original live database is appearing in my queries. This is despite the file timestamps of the copy not changing at all. It is also causing some slowdown in the live database. My understanding is that the .mdb files are standalone, or is this not the case? Should I have copied the database in a different way?

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  • Keeping connection to APNs open on App Engine using Modules in Go

    - by user3727820
    I'm trying to implement iOS push notifications for a messageboard app I've written (so like notification for new message ect. ect.) but have no real idea where to start. Alot the current documentation seems to be out of date in regard to keeping persistent TLS connections open to the APNs from App Engine and links to articles about depreciated backends I'm using the Go runtime and just keep getting stuck. For instance, the creation of the socket connection to APNs requires a Context which can only be got from a HTTP request, but architecturally this doesn't seem to make a lot of sense because ideally the socket remains open regardless. Is there any clearer guides around that I'm missing or right now is it a better idea to setup a separate VPS or compute instance to handle it?

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  • Shortest command to calculate the sum of a column of output on Unix?

    - by Andrew
    I'm sure there is a quick and easy way to calculate the sum of a column of values on Unix systems (using something like awk or xargs perhaps), but writing a shell script to parse the rows line by line is the only thing that comes to mind at the moment. For example, what's the simplest way to modify the command below to compute and display the total for the SEGSZ column (70300)? ipcs -mb | head -6 IPC status from /dev/kmem as of Mon Nov 17 08:58:17 2008 T ID KEY MODE OWNER GROUP SEGSZ Shared Memory: m 0 0x411c322e --rw-rw-rw- root root 348 m 1 0x4e0c0002 --rw-rw-rw- root root 61760 m 2 0x412013f5 --rw-rw-rw- root root 8192

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