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• How to implement Horner's scheme for multivariate polynomials?

  - by gsreynolds

  Background I need to solve polynomials in multiple variables using Horner's scheme in Fortran90/95. The main reason for doing this is the increased efficiency and accuracy that occurs when using Horner's scheme to evaluate polynomials. I currently have an implementation of Horner's scheme for univariate/single variable polynomials. However, developing a function to evaluate multivariate polynomials using Horner's scheme is proving to be beyond me. An example bivariate polynomial would be: 12x^2y^2+8x^2y+6xy^2+4xy+2x+2y which would factorised to x(x(y(12y+8))+y(6y+4)+2)+2y and then evaluated for particular values of x & y. Research I've done my research and found a number of papers such as: staff.ustc.edu.cn/~xinmao/ISSAC05/pages/bulletins/articles/147/hornercorrected.pdf citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.40.8637&rep=rep1&type=pdf www.is.titech.ac.jp/~kojima/articles/B-433.pdf Problem However, I'm not a mathematician or computer scientist, so I'm having trouble with the mathematics used to convey the algorithms and ideas. As far as I can tell the basic strategy is to turn a multivariate polynomial into separate univariate polynomials and compute it that way. Can anyone help me? If anyone could help me turn the algorithms into pseudo-code that I can implement into Fortran myself, I would be very grateful.

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• mmap() for large file I/O?

  - by Boatzart

  I'm creating a utility in C++ to be run on Linux which can convert videos to a proprietary format. The video frames are very large (up to 16 megapixels), and we need to be able to seek directly to exact frame numbers, so our file format uses libz to compress each frame individually, and append the compressed data onto a file. Once all frames are finished being written, a journal which includes meta data for each frame (including their file offsets and sizes) is written to the end of the file. I'm currently using ifstream and ofstream to do the file i/o, but I am looking to optimize as much as possible. I've heard that mmap() can increase performance in a lot of cases, and I'm wondering if mine is one of them. Our files will be in the tens to hundreds of gigabytes, and although writing will always be done sequentially, random access reads should be done in constant time. Any thoughts as to whether I should investigate this further, and if so does anyone have any tips for things to look out for? Thanks!

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• Project design / FS layout for large django projects

  - by rcreswick

  What is the best way to layout a large django project? The tutuorials provide simple instructions for setting up apps, models, and views, but there is less information about how apps and projects should be broken down, how much sharing is allowable/necessary between apps in a typical project (obviously that is largely dependent on the project) and how/where general templates should be kept. Does anyone have examples, suggestions, and explanations as to why a certain project layout is better than another? I am particularly interested in the incorporation of large numbers of unit tests (2-5x the size of the actual code base) and string externalization / templates.

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• Using the value of a variable as another variables name in Ruby

  - by hrickards

  Hi, I'm just starting out in learning Ruby and I've written a program that generates some numbers and assigns them to variables @one, @two, @three etc. The user can then specify a variable to change by inputting it's name (e.g one). I then need to do something like '@[valueofinout] = asd'. How would I do this, and is there a better way as the way I'm thinking of seems to be discouraged? I've found x = "myvar" myvar = "hi" eval(x) -> "hi" but I don't completely understand why the second line is needed. In my case would I use something like @one = "21" input = "one" input = "@" + input changeto = "22" eval(input) -> changeto Thanks

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• How to find an available port?

  - by Roman

  I want to start a server which listen to a port. I can specify port explicitly and it works. But I would like to find a port in an automatic way. In this respect I have two questions. In which range of port numbers should I search for? (I used ports 12345, 12346, and 12347 and it was fine). How can I find out if a given port is not occupied by another software?

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• Why won't this SQL CAST work?

  - by Kev

  I have a nvarchar(50) column in a SQL Server 2000 table defined as follows: TaskID nvarchar(50) NULL I need to fill this column with some random SQL Unique Identifiers (I am unable to change the column type to uniqueidentifier). I tried this: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar) but I got the following error: Msg 8115, Level 16, State 2, Line 1 Arithmetic overflow error converting expression to data type nvarchar. I also tried: UPDATE TaskData SET TaskID = CAST(NEWID() AS nvarchar(50)) but then got this error: Msg 8152, Level 16, State 6, Line 1 String or binary data would be truncated. I don't understand why this doesn't work but this does: DECLARE @TaskID nvarchar(50) SET @TaskID = CAST(NEW() AS nvarchar(50)) I also tried CONVERT(nvarchar, NEWID()) and CONVERT(nvarchar(50), NEWID()) but got the same errors.

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• Dynamic programming: Find largest diamond (rhombus)

  - by Darksody

  I have a small program to do in Java. I have a 2D array filled with 0 and 1, and I must find the largest rhombus (as in square rotated by 90 degrees) and their numbers. Example: 0 1 0 0 0 1 1 0 1 1 1 0 1 0 1 1 1 1 0 1 1 1 1 1 0 0 1 1 1 1 1 1 1 1 1 1 Result: 1 1 1 1 1 1 1 1 1 1 1 1 1 The problem is similar to this SO question. If you have any idea, post it here.

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• How to define a varying length of the string in XSD pattern?

  - by infant programmer

  The input XML tag must be validated for a pattern which is like this: type : positive int / decimal, minimum length is 0, max length is 12(before decimal point), fraction digits are optional if exist then precision must be 2. This means both positive integer and Decimal numbers(2 digit precision) are allowed. so the acceptable values can be like, null, 0, 0.00, 1234567890, 123456789012, 123456789012.12, invalid values are: 0.000, 1234567890123(13 digits - invalid), The pattern I have designed is: <xs:pattern value="|([0-9]){12}|([0-9]){12}[.][0-9][0-9]"/> The problem with this pattern is, it doesn't allow the number with string-length less than 12, it says "1234567890" is an invalid value, where as it must be allowed!

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• Reading Character from Image

  - by Chinjoo

  I am working on an application which requires matching of numbers from a scanned image file to database entry and update the database with the match result. Say I have image- employee1.jpg. This image will have two two handwritten entries - Employee number and the amount to be paid to the employee. I have to read the employee number from the image and query the database for the that number, update the employee with the amount to be paid as got from the image. Both the employee number and amount to be paid are written inside two boxes at a specified place on the image. Is there any way to automate this. Basically I want a solution in .net using c#. I know this can be done using artificial neural networks. Any ideas would be much appreciated.

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• PHP Resize image down and crop using imagemagick

  - by mr12086

  I'm trying to downsize image uploaded by users at the time of upload. This is no problem but I want to get specific with sizes now. I'm looking for some advice on an algorithm im struggling to produce that will take any shape image - square or rectangle of any widths/heights and downsize it. This image needs to be downsized to a target box size (this changes but is stored in a variable).. So it needs to downsize the image so that both the width and height are larger than the width and height of the target maintaining aspect ratio. but only just.. The target size will be used to crop the image so there is no white space around the edges etc. I'm looking for just the algorithm behind creating the correct resize based on different dimension images - I can handle the cropping, even resizing in most cases but it fails in a few so i'm reaching out. I'm not really asking for PHP code more pseudo. Either is fine obviously. Thanks Kindly.

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• Microsoft Azure compared to "regular" webhosting

  - by Jonas Cannehag

  Hi all, i have an idea of putting my blog on to Azure instead of a regular webhosting company. The only thing i cannot figure out is if that will be cheaper or not. The good part is the getting-knowledge of Azure but on the other hand it is my personal blog and i really don't wanna spend to much money on it. So do you have any idea of how the pricing works? I saw some calculator but didn't manage to understand the numbers. Thanks in advance

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• nth smallest number among two databases of size n each using divide and conquer

  - by urfriend

  we have two databases of size n containing numbers without repeats. So, in total we have 2n elements. They can be accessed through a query to one database at a time. The query is such that you give it a k and it returns kth smallest entry in that database. we need to find nth smallest entry among all the 2n elements in O(logn) queries. the idea is to use divide and conquer but i need some help thinking through this. thanks!

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• How to do a range query

  - by Walter H

  I have a bunch of numbers timestamps that I want to check against a range to see if they match a particular range of dates. Basically like a BETWEEN .. AND .. match in SQL. The obvious data structure would be a B-tree, but while there are a number of B-tree implementations on CPAN, they only seem to implement exact matching. Berkeley DB has the same problem; there are B-tree indices, but no range matching. What would be the simplest way to do this? I don't want to use an SQL database unless I have to. Clarification: I have a lot of these, so I'm looking for an efficient method, not just grep over an array.

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• Comparing numeric strings

  - by Kiren Siva

  From the question PHP Type-Juggling and (strict) Greater/Lesser Than Comparisons I know PHP interpret strings as numbers whenever it can. "10" < "1a" => 10 less than 1 expecting false "1a" < "2" => 1 less than 2 expecting true "10" > "2" => 10 greater than 2 expecting true But in the case of "10" < "1a" php returns true. I am not understanding the concept please help me to clarify it. Edit: But when I add "10" + "1a" it returns 11 that means php interprets "10" as 10 and "1a" as 1. Is that correct?

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• Integration (math) in C++

  - by Chris Thompson

  Hi all, I'm looking for a library to find the integral of a given set of random data (rather than a function) in C++ (or C, but preferably C++). There is another question asking about integration in C but the answers discuss more how to integrate a function (I think...). I understand that this can be done simply by calculating the area under the line segment between each pair of points from start to finish, but I'd rather not reinvent the wheel if this has already been done. I apologize in advance if this is a duplicate; I searched pretty extensively to no avail. My math isn't as strong as I'd like it so it's entirely possible I'm using the wrong terminology. Thanks in advance for any help! Chris

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• How Do I Pull Info from String

  - by Russ Bradberry

  I am trying to pull dynamics from a load that I run using bash. I have gotten to a point where I get the string I want, now from this I want to pull certain information that can vary. The string that gets returned is as follows: Records: 2910 Deleted: 0 Skipped: 0 Warnings: 0 Each of the number can and will vary in length, but the overall structure will remain the same. What I want to do is be able to get these numbers and load them into some bash variables ie: RECORDS=?? DELETED=?? SKIPPED=?? WARNING=?? In regex I would do it like this: Records: (\d*?) Deleted: (\d*?) Skipped (\d*?) Warnings (\d*?) and use the 4 groups in my variables.

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• asp.net mvc validation must be a number custom error

  - by Para

  Hi, I am new to asp.net and I have a problem. When the users insert in a editor for a decimal field something other than numbers, they get an error "Field name" is not a number. But I don't want them to receive this message I want them to receive another message. I have no problem with this with required and range validators. Is there any way for me to do this? I am not refering necessarily to changing the culture just displaying another message. Thanks.

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• MySQL Rank Not Matching High Score in Table

  - by boddie

  While making a game the MySQL call to get the top 10 is as follows: SELECT username, score FROM userinfo ORDER BY score DESC LIMIT 10 This seems to work decently enough, but when paired with a call to get a individual player's rank the numbers may be different if the player has a tied score with other players. The call to get the players rank is as follows: SELECT (SELECT COUNT(*) FROM userinfo ui WHERE (ui.score, ui.username) >= (uo.score, uo.username)) AS rank FROM userinfo uo WHERE username='boddie'; Example results from first call: +------------+-------+ | username | score | +------------+-------+ | admin | 4878 | | test3 | 3456 | | char | 785 | | test2 | 456 | | test1 | 253 | | test4 | 78 | | test7 | 0 | | boddie | 0 | | Lz | 0 | | char1 | 0 | +------------+-------+ Example results from second call +------+ | rank | +------+ | 10 | +------+ As can be seen, the first call ranks the player at number 8 on the list, but the second call puts him at number 10. What changes or what can I do to make these calls give matching results? Thank you in advance for any help!

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• Source code annotation tool

  - by RoToRa

  I'm looking for a tool with which I can annotate source code. I have some 3rd party source code (JavaScript) I need to understand and I don't want to change it (add inline comments) so that line numbers can stay intact (for communication with others), I can avoid accidentally changing something and my annotations stand out compared to the authors comments. Normally I would print the whole thing out an scribble on it, but the code is too long for that and I need to share it per email. I would be great if one could do some like that including being able to create "links" between so places in the code, possibly even visually with a lines or arrows.

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• I want to query whitepages.com 4,000 times, how to save the results?

  - by John Corbin

  I have an old customer list of 4,000 businesses. I want to determine if the phone numbers associated with each listing are still working (and therefore the business is probably still open). I can put each number in whitepages.com and check them one by one... but want to automate the results. I have looked at their API and can't digest it. I can form the correct query URL, but trying things like cURL -O doesn't work. I have access to Mac tools, Unix tools, and could try various javascript stuff if anyone could point me in the right direction... would even pay. Help? Thx

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• How to use a proprety/value table in MySQL

  - by David

  I inherited a mysql database that has a table with columns like this: object_id, property, value It holds data like this: 1,first_name,Jane 1,last_name,Doe 1,age,10 1,color,red 2,first_name,Mike 2,last_name,Smith 2,age,20 2,color,blue 3,first_name,John 3,last_name,Doe 3,age,20 3,color,red ... Basically what I want to do is treat this table as a regular table. How would I get the id numbers (or all properties) of a person who is age 20 sorted by last and than first name? So far I have: SELECT object_id FROM table WHERE property = 'age' AND value = '20' union SELECT object_id FROM table WHERE property = 'color' AND value = 'red' But I'm not sure how to go about ordering the data. Thanks

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• CakePHP: How do I order results based on a 2-level deep association model?

  - by KcYxA

  I'm hoping I won't need to resort to custom queries. A related question would be: how do I retrieve data so that if an associated model is empty, no record is retrieved at all, as opposed to an empty array for an associated model? As an oversimplified example, say I have the following models: City -- Street -- House How do I sort City results by House numbers? How do I retrieve City restuls that have at least one House in it? I don't want a record with a city name and details and an empty House array as it messes up pagination results. CakePHP retrieves House records belonging to the Street in a separate query, so putting somthing like 'House.number DESC' into the 'order' field of the search query returns a 'field does not exist' error. Any ideas?

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• How to set Chrome's user script version number.

  - by Atli

  Hey. I've been wondering how I might set the version number displayed for user-scripts in Chrome's extension tab So far the obvious methods have failed: // ==UserScript== // @version 1.1.5 // @uso:version 1.1.5 // ==/UserScript== I know Greasemonkey for Firefox doesn't use a version value, but since Chrome actually displays a version number, I thought it might. Perhaps this is a feature that has not been implemented? Or maybe it was never intended to be there, but it is there because extensions have version numbers, and user-scripts are currently installed as extensions? (I'm using the Linux beta, version: 4.0.249.43, by the way) Thanks. Edit: Seems this is listed as an unconfirmed bug in the Chromium bug database (Issue 30760)

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• How to file split at a line number

  - by superspace

  I want to split a 400k line long log file from a particular line number. For this question, lets make this an arbitrary number 300k. Is there a linux function that allows me to do this? I know split lets me split the file in equal parts either by size or line numbers but that's not what I want. I want to the first 300k in one file and the last 100k in the second file. Any help would be appreciated. Thanks!

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• The fastest way to iterate through a collection of objects

  - by Trev

  Hello all, First to give you some background: I have some research code which performs a Monte Carlo simulation, essential what happens is I iterate through a collection of objects, compute a number of vectors from their surface then for each vector I iterate through the collection of objects again to see if the vector hits another object (similar to ray tracing). The pseudo code would look something like this for each object { for a number of vectors { do some computations for each object { check if vector intersects } } } As the number of objects can be quite large and the amount of rays is even larger I thought it would be wise to optimise how I iterate through the collection of objects. I created some test code which tests arrays, lists and vectors and for my first test cases found that vectors iterators were around twice as fast as arrays however when I implemented a vector in my code in was somewhat slower than the array I was using before. So I went back to the test code and increased the complexity of the object function each loop was calling (a dummy function equivalent to 'check if vector intersects') and I found that when the complexity of the function increases the execution time gap between arrays and vectors reduces until eventually the array was quicker. Does anyone know why this occurs? It seems strange that execution time inside the loop should effect the outer loop run time.

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