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• fastest calculation of largest prime factor of 512 bit number in python

  - by miraclesoul

  dear all, i am simulating my crypto scheme in python, i am a new user to it. p = 512 bit number and i need to calculate largest prime factor for it, i am looking for two things: Fastest code to process this large prime factorization Code that can take 512 bit of number as input and can handle it. I have seen different implementations in other languages, my whole code is in python and this is last point where i am stuck. So let me know if there is any implementation in python. Kindly explain in simple as i am new user to python sorry for bad english.

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• MongoDb vs Ehcache caching advise for speeding up read only mysql Database

  - by paddydub

  I'm building a Route Planner Webapp using Spring/Hibernate/Tomcat and a mysql database, I have a database containing read only data, such as Bus Stop Coordinates, Bus times which is never updated. I'm trying to make the app run faster, each time the application is run it will preform approx 1000 reads to the database to calculate a route. I have setup a Ehcache which greatly improves the read from database times. I'm now setting terracotta + Ehcache distributed caching to share the cache with multiple Tomcat JVMs. This seems a bit complicated. I've tried memcached but it was not performing as fast as ehcache. I'm wondering if a MongoDb would be better suited. I have no experience with nosql but I would appreciate if anyone has any ideas. All i need is quick access to the read only database.

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• Date object to Calendar [Java]

  - by Samuel

  Hello World, I have a class Movie in it i have a start Date, a duration and a stop Date. Start and stop Date are Date Objects (private Date startDate ...) (It's an assignment so i cant change that) now i want to automatically calculate the stopDate by adding the duration (in min) to the startDate. By my knowledge working with the time manipulating functions of Date is deprecated hence bad practice but on the other side i see no way to convert the Date object to a calendar object in order to manipulate the time and reconvert it to a Date object. Is there a way? And if there is what would be best practice Thanks in advance Samuel

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• [RESTful] Calculation with RESTful web service with MySQL database : )

  - by Dobby

  Dears, I am now making some RESTful web service with MySQL database. I used NetBeans to create the resources of RESTful service with MySQL, and now I can now using GET and POST/PUT to list and add/modify data entities in the MySQL server. Currently, I wish to make some calculations right after a client makes the POST activities, then the posted data with calculated results will be inserted into the MySQL database. I am very new to this, I guess I need to add some functions and call them to calculate but I don't know where and how to do that : ( Could any one help me on this issue? Thanks a lot in advance! : ) Best! Dobby

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• CUDA: accumulate data into a large histogram of floats

  - by shoosh

  I'm trying to think of a way to implement the following algorithm using CUDA: Working on a large volume of voxels, for each voxel I calculate an index i and a value c. after the calculation I need to perform histogram[i] += c c is a float value and the histogram can have up to 15,000 bins. I'm looking for a way to implement this efficiently using CUDA. The first obvious problem is that with compute capabilities 1.3 which is what I'm using I can't even do an atomicAdd() of floats so how can I accumulate anything reliably? This example by nVidia does something somewhat simpler. The histograms are saved in the shared memory (which I can't do due to its size) and it only accumulates integers. Can this approach be generalized to my case?

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• Create a custom worksheet function in Excel VBA

  - by Tomalak

  I have a faint memory of being able to use VBA functions to calculate values in Excel, like this (as the cell formula): =MyCustomFunction(A3) Can this be done? EDIT: This is my VBA function signature: Public Function MyCustomFunction(str As String) As String The function sits in the ThisWorkbook module. If I try to use it in the worksheet as shown above, I get the #NAME? error. Solution (Thanks, codeape): The function is not accessible when it is defined ThisWorkbook module. It must be in a "proper" module, one that has been added manually to the workbook.

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• How to get the data for intra-day candlestick charts for stocks on eg Nasdaq

  - by Chris

  Hi, For a learning exercise, i'm wanting to create candlestick (stock) graphs for stocks using zedgraph. Now on google finance, i can get daily open-high-low-close data which is perfect for making these graphs, but i'm wanting to create intra-day graphs, eg open-high-low-close data for an hour (or 5 mins, or 1 min even). Is there any way to get that kind of data without having to subscribe to any expensive service? I've heard opentick mentioned in an old SO question, but their site is defunct now. I was thinking of polling google finance once a minute to get the latest stock price, then with an hour's worth of 60 prices, i could then roughly calculate the open-high-low-close, but this is a bit of an estimation and i'm open to other suggestions. Cheers all.

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• Customizing Rails XML rendering to include extra properties

  - by Isaac Cambron

  Let's say I have a model like this: create_table :ninjas do |t| t.string name end And the Ninja class with an extra property: class Ninja < ActiveRecord::Base def honorific "#{name}san" end end And in my controller I just want to render it to XML: def show render :xml => Ninja.find(params[:id]) end The honorific part isn't rendered. That makes sense, since it's just a method, but is there a way of tricking it? I'm totally up for answers to the effect of, "You're doing this totally wrong." I'll just add that I really do want to calculate the honorific on the fly, and not, like, store it in the database or something.

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• OpenCV: How to copy CvSeq data into CvMat?

  - by Can Bal

  I have a CvSeq structure at hand, which is the output of an available OpenCV function. This holds 128 bytes of data in each of the sequence elements. I want to copy each of these 128-byte elements into rows of a CvMat structure to form a N-by-128 of type CV_32FC1. What would be the most efficient way to do this? I thought of using memcpy but I couldn't come up with a working solution. For the details, I want to calculate the SURF features in an image by cvExtractSURF() function, and copy the SURF descriptors into a matrix for passing it to the cvKMeans2().

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• Jpeg calculating max size

  - by Doodle

  I have to say the I don't know much about how file formats work. My question is say I have a jpeg file that is 200 px by 200 px, how can one calculate what the maximum size that file could be in terms of megabytes/bytes? I think that the reasoning that led to the question will help some one answer me. I have a Java Applet the uploads Images that people draw with it to my server. I need to know what the max size that this file can conceivably reach. It is always going to be 200x200. It sounds dumb but are there colors that take more byte size then others and if so what is the most expensive one?

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• How to determine MS Access field size via OleDb

  - by Andy

  The existing application is in C#. During startup the application calls a virtual method to make changes to the database (for example a new revision may need to calculate a new field or something). An open OleDb connection is passed into the method. I need to change a field width. The ALTER TABLE statement is working fine. But I would like to avoid executing the ALTER TABLE statement if the field is already the appropriate size. Is there a way to determine the size of an MS Access field using the same OleDb connection?

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• SQL DATEDIFF Not working!?

  - by James

  Hi all, I am running a simple DATEDIFF query but it doesn't seem to calculate the days properly or i'm doing something wrong. If I run PRINT DATEDIFF(Day, 2010-01-20, 2010-01-01) RETURN 19 Which is correct. If i change the month in the first date to Feb (02) I get something strange. PRINT DATEDIFF(Day, 2010-02-20, 2010-01-01) RETURN 20 Now shouldn't it be 48 or something? Can anyone see what i'm doing wrong or is this not the correct function to be using if I want the No of days between these dates? I've tried taking one date from the other: PRINT (2010-02-20) - (2010-01-01) RETURN -20 Any help much appreciated. Thanks J.

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• tcp checksum and tcp offloading

  - by scatman

  i am using raw sockets to create my own socket. i need to set the tcp_checksum. i have tried a lot of references but all are not working (i am using wireshark for testing). could you help me please. by the way, i read somewhere that if you set tcp_checksum=0. then the hardware will calculate the checksum automatically for you. is this true? i tried it, but in wireshark the tcp_checksum gives a value of 0X000 and says tcp offload. i also read about tcp offloading, and didn't understand, is it only that wireshark is cannot check an offloaded tcp checksum, but there is a correct one??

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• System.Net.Mail.MailMessage Raw Content / Spam Assassin

  - by Martin

  Hey everyone, What I am trying to do is pass the raw content of an outgoing email to spamassassin in order to calculate a spam score. I am stuck in how I might get the raw content of the email. My C# code currently just constructs the MailMessage and passes it the SmtpClient's Send() method. Before sending, is there a way to get a raw version of the mail message (as the protocol might see it) so that I can pass this to the spamassassin tool for spam assessment? If I've not explained very well, let me know and I'll try to explain better. Thanks in advance, Martin.

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• Noise Estimation / Noise Measurement in Image

  - by Drazick

  Hello. I want to estimate the noise in an image. Let's assume the model of an Image + White Noise. Now I want to estimate the Noise Variance. My method is to calculate the Local Variance (3*3 up to 21*21 Blocks) of the image and then find areas where the Local Variance is fairly constant (By calculating the Local Variance of the Local Variance Matrix). I assume those areas are "Flat" hence the Variance is almost "Pure" noise. Yet I don't get constant results. Is there a better way? Thanks.

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• Drupal CCK 3 Multigroup tables with views

  - by henrijs.seso

  Hi, Each node have CCK-3-dev multigroup with 3 fields. Can I use one of fields as table header? Values of this field are taken from Taxonomy. With a simple recipe example, where food Z and Y are 2 nodes with recipes and each node has multigroup with ingredient name (milk, fish), amount (numbers) and unit (g, kg). Is there a way to create a table like this with views, I want to use views calc to calculate total amount of ingredient needed to prepare multiple recipes: Ingredient A Ingredient B Ingredient C Food Z 200 g 700 g 0 g Food Y 500 g 1000 g 50 g I don't even need units by number, but that would be good too. Anyways, how do I get this?

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• What's an efficient way of calculating the nearest point?

  - by Griffo

  I have objects with location data stored in Core Data, I would like to be able to fetch and display just the nearest point to the current location. I'm aware there are formulas which will calculate the distance from current lat/long to a stored lat/long, but I'm curious about the best way to perform this for a set of 1000+ points stored in Core Data. I know I could just return the points from Core Data to an array and then loop through that looking for the min value for distance between the points but I'd imagine there's a more efficient method, possibly leveraging Core Data in some way. Any insight would be appreciated. EDIT: I don't know how I missed this on my initial search but this SO question suggests just iterating through an array of Core Data objects but limiting the array size with a bounding box based on the current location. Is this the best I can do?

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• Haskell Lazy Evaluation and Reuse

  - by Jonathan Sternberg

  I know that if I were to compute a list of squares in Haskell, I could do this: squares = [ x ** 2 | x <- [1 ..] ] Then when I call squares like this: print $ take 4 squares And it would print out [1.0, 4.0, 9.0, 16.0]. This gets evaluated as [ 1 ** 2, 2 ** 2, 3 ** 2, 4 ** 2 ]. Now since Haskell is functional and the result would be the same each time, if I were to call squares again somewhere else, would it re-evaluate the answers it's already computed? If I were to re-use squares after I had already called the previous line, would it re-calculate the first 4 values? print $ take 5 squares Would it evaluate [1.0, 4.0, 9.0, 16.0, 5 ** 2]?

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• How to implement a Digg-like algorithm?

  - by Niklas

  Hi, How to implement a website with a recommendation system similar to stackoverflow/digg/reddit? I.e., users submit content and the website needs to calculate some sort of "hotness" according to how popular the item is. The flow is as follows: Users submit content Other users view and vote on the content (assume 90% of the users only views content and 10% actively votes up or down on content) New content is continuously submitted How do I implement an algorithm that calculates the "hotness" of a submitted item, preferably in real-time? Are there any best-practices or design patterns? I would assume that the algorithm takes the following into consideration: When an item was submitted When each vote was cast When the item was viewed E.g. an item that gets a constant trickle of votes would stay somewhat "hot" constantly while an item that receives a burst of votes when it is first submitted will jump to the top of the "hotness"-list but then fall down as the votes stop coming in. (I am using a MySQL+PHP but I am interested in general design patterns).

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• Accessing ruby counter cache

  - by Julian

  Hi all, I'm playing around with a fork of acts_as_taggable_on_steroids as a learning exercise. The version I'm looking at does some stuff I don't understand to calculate Tag counts. So I thought I'd do a version using PORC (Plain Old Rails Counters): class Tagging < ActiveRecord::Base #:nodoc: belongs_to :tag, :counter_cache => "tagging_counter_cache" ... I thought tagging_counter_cache was transparently accessed when I access tag.taggings.count but apparently not? Do I really have to access tag.tagging_counter_cache explicitly? >> tag.taggings.count SQL (0.7ms) SELECT count(*) AS count_all FROM `taggings` WHERE (`taggings`.tag_id = 16) Same for size. It's cool if that's the case but just wanted to check.

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• Distance by sea calculator, intermediate coordinates?

  - by Lucian2k

  How do I calculate distance between 2 coordinates by sea? I also want to be able to draw a route between the two coordinates. Only solution I found so far is to split a map into pixels, identify each pixel as LAND or SEA and then try to find the path using A* algorithm. Then transform pixels to relative coordinates. There are some software packages I could buy but none have online extensions. A service that calculates distances between sea ports and plots the path on a map is searates.com

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• Face recognition Library

  - by Janusz

  I'm looking for a free face recognition library for a university project. I'm not looking for face detection. I'm looking for actual recognition. That means finding images that contain specified faces or libraries that calculate distances between specific faces. I'm using OpenCV for detecting the faces and a rough Eigenfaces Algorithm for the recognition now. But I thought there should be something out there with a better performance then a self written Eigenfaces Algorithm. I don't talk about speed as performance I'm looking for a library with better results as an simple Eigenfaces approach I took a look at faint but it seems the library is not very reusable for my own applications. I'm happy with a library in Python, Java, C++, C or something like that. The best thing would be if it can be run on a Windowsmachine

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• Graph Theory: How to compute closeness centrality for each node in a set of data?

  - by Jordan

  I'd like to learn how to apply network theory to my own cache of relational data. I'm trying to build a demo of a new way of browsing a music library, using network theory, that I think would make for a very intuitive and useful way of finding the right song at any given time. I have all the data (artists as nodes, similarity from 0 to 1 between each artist and those it is related to) and I can already program, but I don't know how to actually calculate the centrality of a node from that. I've spent a while trying to email different professors at my school but no one seems to know where I can learn this. I hope someone's done something similar. Thanks in advance you guys! ~Jordan

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• Compute average distance from point to line segment and line segment to line segment

  - by Fred

  Hi everyone, I'm searching for an algorithm to calculate the average distance between a point and a line segment in 3D. So given two points A(x1, y1, z1) and B(x2, y2, z2) that represent line segment AB, and a third point C(x3, y3, z3), what is the average distance between each point on AB to point C? I'm also interested in the average distance between two line segments. So given segment AB and CD, what is the average distance from each point on AB to the closest point on CD? I haven't had any luck with the web searches I've tried, so any suggestions would be appreciated. Thanks.

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• PHP/MySQL database connection priority?

  - by Josh

  Hello, I have a production database where usage statistics for a service we're working on. I use php to periodically roll up different resolutions (day, week, month, year) of interesting statistics in buckets dictated by the resolution. The php application I've written "completes" its data when its run, such that it will calculate all the rolled-up statistics for the resolutions and periods since it was last run. This is useful if we want to turn this off to debug database performance issues, because I can turn it back on and have it complete its data set. The problem I have, is the calculations are fairly intensive and drive the QPS of the production database server up. Is there a way to set a "priority" on a particular database connection so that it will only use "off-cycles" to do these calculations? Maybe a proper response would be to replicate the tables I'm working on into a different stats database, but, unfortunately I don't have the resources in place to attempt such a thing (yet). Thanks in advance for any help, Josh

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