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• Pohlig–Hellman algorithm for computing discrete logarithms

  - by drelihan

  Hi Folks, I'm working on coding the Pohlig-Hellman Algorithm but I am having problem understand the steps in the algorithm based on the definition of the algorithm. Going by the Wiki of the algorithm: http://en.wikipedia.org/wiki/Pohlig%E2%80%93Hellman_algorithm I know the first part 1) is to calculate the prime factor of p-1 - which is fine. Howeever, I am not sure what I need to do in steps 2) and 3). Can someone help with explaining this in plain english (i) - or pseudocode. I want to code the solution myself obviously but I cannot make any more progress unless i understand the algorithm. Note: I have done a lot of searching for this and I read S. Pohlig and M. Hellman (1978). "An Improved Algorithm for Computing Logarithms over GF(p) and its Cryptographic Significance but its still not really making sense to me. Thanks in advance

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• What is the complexity of the below code with respect to memory ?

  - by Cshah

  Hi, I read about Big-O Notation from here and had few questions on calculating the complexity.So for the below code i have calculated the complexity. need your inputs for the same. private void reverse(String strToRevers) { if(strToRevers.length() == 0) { return ; } else { reverse(strToRevers.substring(1)); System.out.print(strToRevers.charAt(0)); } } If the memory factor is considered then the complexity of above code for a string of n characters is O(n^2). The explanation is for a string that consists of n characters, the below function would be called recursively n-1 times and each function call creates a string of single character(stringToReverse.charAT(0)). Hence it is n*(n-1)*2 which translates to o(n^2). Let me know if this is right ?

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• UrlEncoding-Safe Delimiter

  - by Aren B

  So the site I'm working on has a filter system that operates by passing a key and value system through a querystring. The whole site is going through a re-factor soon and I'm maintaining the existing site so before we discuss the RIGHT way to implement this, I just need ideas for changing my delimiter. The current format is like this: cf=<key>:<value> The problem is, I've recently run into an issue because some of our new values for this filter contain : in them. I.e: cf=MO_AspectRatio:16:10 The value is being UrlEncoded, but the browsers are de-coding %3a into : on the fly because the : doesn't inherently break the urls. I need some suggestions for url-safe delimiters that aren't :,-,_,&,? that makes sense. I'm not looking for a solution like () or something wild.

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• Short unique id in php

  - by Antti

  I want to create a unique id but uniqid() is giving something like '492607b0ee414'. What i would like is something similar to what tinyurl gives: '64k8ra'. The shorter, the better. The only requirements are that it should not have an obvious order and that it should look prettier than a seemingly random sequence of numbers. Letters are preferred over numbers and ideally it would not be mixed case. As the number of entries will not be that many (up to 10000 or so) the risk of collision isn't a huge factor. Any suggestions appreciated.

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• Should developers know how to use office suites?

  - by systempuntoout

  How deep is your knowledge on Office suites? Personally i don't like them, i hate create and manage word documents, excel datasheets etc. etc. I'm not talking about opening a word document and write some text or calculate sum and division on excel; i'm talking about advanced features like revisions, vba macros and so on. I have a co-worker, actually he's a talented functional analyst, that don't know anything about programming but he's kind a monster guru on Microsoft Office suite. When he sits on my desk and asks me to open and modify some of his hardly complicated Microsoft Excel multicolor multipivotal recursive datasheet, ehm, i feel like a baby in front of a nuclear plant console.It' not a great feeling if you know what i mean. As programmer, do you feel guilty about not knowing office suites enough?

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• Is this an F# quotations bug?

  - by ControlFlow

  [<ReflectedDefinition>] let rec x = (fun() -> x + "abc") () The sample code with the recursive value above produces the following F# compiler error: error FS0432: [<ReflectedDefinition>] terms cannot contain uses of the prefix splice operator '%' I can't see any slicing operator usage in the code above, looks like a bug... :) Looks like this is the problem with the quotation via ReflectedDefinitionAttribute only, normal quotation works well: let quotation = <@ let rec x = (fun() -> x + "abc") () in x @> produces expected result with the hidden Lazy.create and Lazy.force usages: val quotation : Quotations.Expr<string> = LetRecursive ([(x, Lambda (unitVar, Application (Lambda (unitVar0, Call (None, String op_Addition[String,String,String](String, String), [Call (None, String Force[String](Lazy`1[System.String]), [x]), Value ("abc")])), Value (<null>)))), (x, Call (None, Lazy`1[String] Create[String](FSharpFunc`2[Unit,String]), [x])), (x, Call (None, String Force[String](Lazy`1[String]), [x]))], x) So the question is: is this an F# compiler bug or not?

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• Entire website in Silverlight 4. Practical or not?

  - by Sahat

  Similar question: Using Silverlight for an entire website? That question is over 2 years old. Silverlight has gone a long way from Silverlight 1.0 Beta 1 to Silverlight 4.0 Final. Would it be practical to create a full Silverlight web application these days? I plan to deploy the website sometime around Q1 2011. I have thought about going ASP.NET + AJAX way, but it just won't give me the same rich features as Silverlight. A lot of people when they hear ASP.NET or Silverlight instantly think about business or enterprise applications. But all I want to create is a fansite, with rich user interface and a great "WOW" factor.

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• Tomcat6 MySql JDBC Datasource configuration

  - by Bob

  Hi, I've always used Spring's dependency injection to get datasource objects and use them in my DAOs, but now, I have to write an app without that. With Spring I can write something like this: <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://127.0.0.1/app?characterEncoding=UTF-8" /> <property name="username" value="u" /> <property name="password" value="p" /> </bean> But how can I use datasource in my DAOs without Spring or anything? I'm using servlets and JSPs only. Performance is very important factor. Thanks in advance!

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• What is the relationship between recursion functions and memory stack?

  - by Eslam

  is there's a direct relationship between recursive functions and the memory stack, for more explanation consider that code: public static int triangle(int n) { System.out.println(“Entering: n = ” + n); if (n == 1) { System.out.println(“Returning 1”); return 1; } else { int temp = n + triangle(n - 1); System.out.println(“Returning“ + temp); return temp; } }? in this example where will the values 2,3,4,5 be stored until the function returns ? note that they will be returned in LIFO(LastInFirstOut) is these a special case of recursion that deals with the memory stack or they always goes together?

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• Strange PHP reference bug

  - by Roland Soós

  Hello, I have a really strange bug with my PHP code. I have a recursive code which build up a menu tree with object and one of my customers server can't make it work. Contructor: function Menu(&$menus, &$keys , &$parent, &$menu){ ... if($keys === NULL){ $keys = array_keys($menus); } ... for($x = 0; $x < count($keys); $x++) { var_dump($keys); $menu = $menus[$keys[$x]]; var_dump($keys); if($this->id == $menu->pid){ $keys[$x] = NULL; $this->submenus[] = new Menu($menus, $keys, $this, $menu); } } First var_dump give me back the array, the second give back the first element of $menus. Do you have any idea what causes this? PHP version 5.2.3

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• elegant way to make directory recursively in Python?

  - by user248237

  I would like to make a directory in a "recursive" way, i.e. have a function make_directory() that behaves as follows: make_directory("a/b/c/d/") should create directory a, then child b, then c, then d. If any of the parent directories exist it should not make them. E.g. if "a" exists, then b should be a subdir of that, and then c should be made inside b, etc. how can I do this in python? os.mkdir does not have this behavior.

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• Downsampling and applying a lowpass filter to digital audio

  - by twk

  I've got a 44Khz audio stream from a CD, represented as an array of 16 bit PCM samples. I'd like to cut it down to an 11KHz stream. How do I do that? From my days of engineering class many years ago, I know that the stream won't be able to describe anything over 5500Hz accurately anymore, so I assume I want to cut everything above that out too. Any ideas? Thanks. Update: There is some code on this page that converts from 48KHz to 8KHz using a simple algorithm and a coefficient array that looks like { 1, 4, 12, 12, 4, 1 }. I think that is what I need, but I need it for a factor of 4x rather than 6x. Any idea how those constants are calculated? Also, I end up converting the 16 byte samples to floats anyway, so I can do the downsampling with floats rather than shorts, if that helps the quality at all.

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• Help needed inorder to avoid recursion

  - by Srivatsa

  Hello All I have a method, which gives me the required number of Boxes based on number of devices it can hold.Currently i have implemented this logic using recursion private uint PerformRecursiveDivision(uint m_oTotalDevices,uint m_oDevicesPerBox, ref uint BoxesRequired) { if (m_oTotalDevices< m_oDevicesPerBox) { BoxesRequired = 1; } else if ((m_oTotalDevices- m_oDevicesPerBox>= 0) && (m_oTotalDevices- m_oDevicesPerBox) < m_oDevicesPerBox) { //Terminating condition BoxesRequired++; return BoxesRequired; } else { //Call recursive function BoxesRequired++; return PerformRecursiveDivision((m_oTotalDevices- m_oDevicesPerBox), m_oDevicesPerBox, ref BoxesRequired); } return BoxesRequired; } Is there any better method to implement the same logic without using recursion. Cos this method is making my application very slow for cases when number of devices exceeds 50000. Thanks in advance for your support Constant learner

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• image scaling with C

  - by sa125

  Hi - I'm trying to read an image file and scale it by multiplying each byte by a scale its pixel levels by some absolute factor. I'm not sure I'm doing it right, though - void scale_file(char *infile, char *outfile, float scale) { // open files for reading FILE *infile_p = fopen(infile, 'r'); FILE *outfile_p = fopen(outfile, 'w'); // init data holders char *data; char *scaled_data; // read each byte, scale and write back while ( fread(&data, 1, 1, infile_p) != EOF ) { *scaled_data = (*data) * scale; fwrite(&scaled_data, 1, 1, outfile); } // close files fclose(infile_p); fclose(outfile_p); } What gets me is how to do each byte multiplication (scale is 0-1.0 float) - I'm pretty sure I'm either reading it wrong or missing something big. Also, data is assumed to be unsigned (0-255). Please don't judge my poor code :) thanks

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• How to use Page Object pattern with Cucumber and Webrat / Selenium?

  - by Will Sargent

  I'm looking at a cucumber test suite that is somewhat brittle right now; many small steps, and no knowledge of the page itself. I'd like to factor out the logic involved in the step definitions inside a series of Selenium PageObjects. As seen here. However, because I'm using Webrat and not Selenium, everything has to go through the Webrat model. So I cannot do class MyPage < Selenium::WebPage end because that adds a direct dependency. So I have to route everything through Webrat while still maintaining the Selenium Page object goodness. No documentation on this that I can see: if someone has anything on Webrat + PageModel I'd love to see it.

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• Math algorithm question

  - by Senica Gonzalez

  I'm not sure if this can be done without some determining factor....but wanted to see if someone knew of a way to do this. I want to create a shifting scale for numbers. Let's say I have the number 26000. I want the outcome of this algorithm to be 6500; or 25% of the original number. But if I have the number 5000, I want the outcome to be 2500; or 50% of the original number. The percentages don't have to be exact, this is just an example. I just want to have like a sine wave sort of thing. As the input number gets higher, the output number is a lower percentage of the input. Does that make sense?

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• Modify cmd.exe properties using the command prompt

  - by CodexArcanum

  Isn't that nicely recursive? I've got a portable command prompt on my external drive, and it has a nice .bat file to configure some initial settings, but I'd like more! Here's what I know how to set from .bat: Colors = (color XY) where x and y are hex digits for the predefined colors Prompt = (prompt $p$g) sets the prompt to "C:\etc\etc " the default prompt Title = (title "text") sets the window title to "text" Screen Size = (mode con: cols=XX lines=YY) sets the columns and lines size of the window Path = (SET PATH=%~d0\bin;%PATH%) sets up local path to my tools and appends the computer's path So that's all great. But there are a few settings I can't seem to set from the bat. Like, how would I set these up wihtout using the Properties dialogue: Buffer = not screen size, but the buffer Options like quick edit mode and autocomplete Popup colors Font. And can you use a font on the portable drive, or must it be installed to work? Command history options

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• Change color on single-series line chart using rCharts and Highcharts?

  - by Sharon

  Is it possible to change the color of a line using rCharts and Highcharts so that the line color changes depending on a factor? I've done this with ggplot2 but would like to make an interactive version if possible. I've tried h1 <- Highcharts$new() h1$chart(type="line") h1$series(data=mydf$myvalue, name="", groups = c("myfactor")) h1$xAxis(tickInterval = 4, categories = mydf$myXaxis) but that's not working, line stays the same color. Sample data myvalue <- c(16, 18, 5, 14, 10) myXaxis <- c(1,2,3,4,5) myfactor <- c("old", "old", "old", "new", "new") mydf <- data.frame(myvalue, myXaxis, myfactor) Thanks for any suggestions.

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• Integrating GSL onto iPhone Xcode

  - by zeroinverse

  I have been trying to integrate GSL (Gnu Scientific Library) into an iPhone project using Xcode. The challenge is GSL has all the modules in different folders, yet when their header files are reference, they often reference instead of or . At least with I could use Xcode's recursive header file search to find it. But with , basically file not found. Does anyone have an easy way to address the hierarchical GSL structure to compile into Xcode? I can do it the tedious way of fixing all the #INCLUDE lines but hoping there is a better alternative. This way, I can more easily update GSL when changes are made by the community. NOTE: I found Xcode needs to find the right header file locations (make sure to adjust your TARGET Build settings, not just your Project Build settings).

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• What one-time-password devices are compatible with mod_authn_otp?

  - by netvope

  mod_authn_otp is an Apache web server module for two-factor authentication using one-time passwords (OTP) generated via the HOTP/OATH algorithm defined in RFC 4226. The developer's has listed only one compatible device (the Authenex's A-Key 3600) on their website. If a device is fully compliant with the standard, and it allows you to recover the token ID, it should work. However, without testing, it's hard to tell whether a device is fully compliant. Have you ever tried other devices (software or hardware) with mod_authn_otp (or other open source server-side OTP program)? If yes, please share your experience :)

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• How to put a newline into a column header in an xtable in R

  - by PaulHurleyuk

  I have a dataframe that I am putting into a sweave document using xtable, however one of my column names is quite long, and I would like to break it over two lines to save space calqc_table<-structure(list(RUNID = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), ANALYTEINDEX = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), ID = structure(1:11, .Label = c("Cal A", "Cal B", "Cal C", "Cal D", "Cal E", "Cal F", "Cal G", "Cal H", "Cal High", "Cal Low", "Cal Mid"), class = "factor"), mean_conc = c(200.619459644855, 158.264703128903, 102.469121407733, 50.3551544728544, 9.88296440865076, 4.41727762501703, 2.53494715706024, 1.00602831741361, 199.065054555735, 2.48063347296935, 50.1499780776199), sd_conc = c(2.3275711264554, NA, NA, NA, NA, NA, NA, 0.101636943231162, 0, 0, 0), nrow = c(3, 1, 1, 1, 1, 1, 1, 3, 2, 2, 2)), .Names = c("Identifier of the Run within the Study", "ANALYTEINDEX", "ID", "mean_conc", "sd_conc", "nrow"), row.names = c(NA, -11L ), class = "data.frame") calqc_xtable<-xtable(calqc_table) I have tried putting a newline into the name, but this didn't seem to work names(calqc_table)[1]<-"Identifier of the \nRun within the Study" Is there a way to do this ? I have seen someone suggest using the latex function from the hmisc package to manually iterate over the table and write it out in latex manually, including the newline, but this seems like a bit of a faf !

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• Tail recursion in Erlang

  - by dagda1

  Hi, I am really struggling to understand tail recursion in Erlang. I have the following eunit test: db_write_many_test() -> Db = db:new(), Db1 = db:write(francesco, london, Db), Db2 = db:write(lelle, stockholm, Db1), ?assertEqual([{lelle, stockholm},{francesco, london}], Db2). And here is my implementation: -module(db) . -include_lib("eunit/include/eunit.hrl"). -export([new/0,write/3]). new() -> []. write(Key, Value, Database) -> Record = {Key, Value}, [Record|append(Database)]. append([H|T]) -> [H|append(T)]; append([]) -> []. Is my implementation tail recursive and if not, how can I make it so? Thanks in advance

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• Feeding a Drill Down Menu with categories, subcategories and subSubcategories from a database

  - by Hassan

  Hi everyone, I have a Drill Down menu and I want to have it gets its elements from a database, I am using php and MySQL and the table (categories) looks like this : http://yfrog.com/jctablehsj I can't figure out how I can extract these information in a way I could put it inside the Drill Down Menu ! I found the recursive method (with LEFT JOINs) and the nested method which I barely understood and again I couldn't apply it to the Drill Down Menu. I found that some people found out a solution with left join and group by but couldn't understand or copy their example ! I would be more than gratefull if you could give me the extact of the query. Thanks a lot for your hard work, Hassan

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• Is It Possible To Use Javascript/CSS To Swap Style Sheets When A Mobile Device Rotates?

  - by Sean M

  I am working on a site that must be designed with mobile accessibility in mind. As part of our brainstorming, we wondered whether it's possible to detect, for a mobile browser (i.e. Mobile Safari or the Android browser), when the viewing device has changed orientation, and to use that as a trigger to change page content? As the title of this question implies, our best-case scenario is the ability to detect the orientation change and use it to alter the CSS on the fly so as to present a slightly different page for landscape versus portrait. Of course we can just design for a page that looks good one way and make it obvious that it's supposed to be viewed that way, but the cool-stuff factor of a page that looks good either way is pretty appealing. Is this idea implementable? Practical?

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• C++ Primer (Stanley Lipmann) or The C++ programming language (special edition)

  - by Kim

  I have a Computer Science degree (long2 time ago) .. I do know Java OOP but i am now trying to pick up C++. I do have C and of course data structure using C or pascal. I have started reading Bjarne Stroustrup book (The C++ Programming Language - Special Edition) but find it extremely difficult esp. some section which i don't have exposure such as Recursive Descent Parser (chapter 6). In terms of the language i don't foresee i have problem but i have problem as mentioned cos' those topic are usually covered in a Master Degree program such as construction of compiler. I just bought a book called C++ primer (Stanley Lipmann) which i heard it is a very good book for C++. Only setback is it's of course no match with the amount of information from the original C++ creator. Please advice. Thanks.

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