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  • Elliptic Curve Diffie-Hellman

    - by cmaduro
    Does the Elliptic curve diffie hellman calculation look any different from the standard one defined here: /* * The basic Diffie-Hellman Key Agreement Equation * * The client initiates * A = g^a mod p * * Sends (g p A) to the server * * The server calculates B * B = g^b mod p * * Sends B back to client * * The client calculates K * K = B^a mod p * * The server calucaltes K * K = A^b mod p * */ Or is it just a specific way of selecting g, a, p and b? How are g,a,p and b selected anyway?

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  • are deleted entries counted in the load factor of a hash table using open addressing

    - by Dr. Monkey
    When calculating the load factor of a hashtable with an open-addressing array implementation I am using: numberOfKeysInArray/sizeOfArray however it occurred to me that since deleted entries must be marked as such (to distinguish them from empty spaces), it might make sense to include these in the number of keys. My thinking is that as far as estimating the average number of probes to find an entry, deleted entries should count towards the load factor, but as far as inserting a new key they should not. Which is the proper calculation: including deleted keys or not?

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  • Is there a Java library with 3D spline functions?

    - by Liam
    In particular, I need a way to represent a curve/spline that passes through a set of known 3D points, and a way of finding other points on the curve/spline, by subdivision/interpolation. For example, if I have a set of points P0 to PN, I want to find 100 points between P0 and P1 that are on a spline that passes through P0 and P1. I see that Java3D's KBRotPosScaleSplinePathInterpolator performs such a calculation, but it is tied to that API's scenegraph model and I do not see how to return the values I need.

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  • HT create a new vector in data frame that takes correlation of existing vectors

    - by Milktrader
    I have a time series of two indexes, with each row representing the closing price on the same day. I'd like to go to row 30 and lookback over the last 30 'days' and calculate the pearson correlation. And then store that value in a new vector. Then, repeat the calculation for the entire time series. It is a trivial task in Excel, so I'm convinced it can be done in R. I don't know the method to use though.

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  • PHP Calculating future date by adding days to a variable date

    - by OneNerd
    I was looking at this post, and it is close to what I need: http://stackoverflow.com/questions/1669165/php-how-to-count-60-days-from-the-add-date However, in that post, the calculation is performed by adding 60 days to the current date. What I need to do is calculate the date based on a variable date (and not the current date). Something like this: $my_date = $some_row_from_a_database; $date_plus_10_days = ???; Anyone know how to do that? Thanks

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  • Java - simple division in Java ---> bug/feature?!

    - by msr
    Hello, Im astonished. Im trying this simple calculation in a Java application: System.out.println("b=" + (1 - 7/10)); Obviously Im wainting for "b=0.3" in the output but here's what I get: b=1 What?! Why this happens? If I make: System.out.println("b=" + (1-0.7)); I get the right result which is "b=0.3". What's going wrong here? Thanks!

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  • Round date to fiscal year

    - by Dave Jarvis
    The following database view rounds the date back to the closest fiscal year (April 1st): CREATE OR REPLACE VIEW FISCAL_YEAR_VW AS SELECT CASE WHEN to_number(to_char( SYSDATE, 'MM' )) < 4 THEN to_date('1-APR-'||to_char(add_months(SYSDATE, -12), 'YYYY'), 'dd-MON-yyyy') ELSE to_date('1-APR-'||to_char(SYSDATE, 'YYYY'), 'dd-MON-yyyy') END AS fiscal_year FROM dual; This allows us to calculate the current fiscal year based on today's date. How can this calculation be simplified or optimized?

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  • hibernate sybase db power function

    - by Vipin Thomas
    We are trying to use sybase function power to do mathematical calculation for one of the DB columns. The hibernate is generating power function as pow(?, xyzo0_.AmtScale) whereas sybase supports power function as Syntax POWER( numeric-expression-1, numeric-expression-2 ) We have tried modifying the hibernate.dialect. Have tried org.hibernate.dialect.SybaseASE15Dialect org.hibernate.dialect.Sybase11Dialect org.hibernate.dialect.SybaseAnywhereDialect but all dialects generate the power function as pow(?, xyzo0_.AmtScale). Is this hibernate issue or are we missing something?

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  • Why would Ruby fail equality on 2 floats that appear the same?

    - by btelles
    Hi there, I have a calculation that generates what appears to be the Float 22.23, and a literal 22.23 like so: some_object.total => 22.23 some_object.total.class => Float 22.23 => 22.23 22.23.class => Float But for some reason, the following is false: some_object.total == 22.23 ? true : false Wacky, right? Is there some kind of precision mechanism being used that maybe isn't completely transparent through the some_object.total call?

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  • comparing data via a function

    - by tigermain
    I have two sets of data (locations) in seperate tables and I need to compare if they match or not. I have a UDF which performs a calculation based upon 5 values from each table. How do I perform a select with a join using this udf? my udf is basically defined by.... ALTER FUNCTION [dbo].[MatchRanking] ( @Latitude FLOAT , @Longitude FLOAT , @Postcode VARCHAR(16) , @CompanyName VARCHAR(256) , @TelephoneNumber VARCHAR(32) , @Latitude2 FLOAT , @Longitude2 FLOAT , @Postcode2 VARCHAR(16) , @CompanyName2 VARCHAR(256) , @TelephoneNumber2 VARCHAR(32) ) RETURNS INT

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  • how to test or describe endless possibilities?

    - by koen
    Example class in pseudocode: class SumCalculator method calculate(int1, int2) returns int What is a good way to test this? In other words how should I describe the behavior I need? test1: canDetermineSumOfTwoIntegers or test2: returnsSumOfTwoIntegers or test3: knowsFivePlusThreeIsEight Test1 and Test2 seem vague and it would need to test a specific calculation, so it doesn't really describe what is being tested. Yet test3 is very limited. What is a good way to test such classes?

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  • Java - simple division in Java ---> bug?!

    - by msr
    Hello, Im astonished. Im trying this simple calculation in a Java application: System.out.println("b=" + (1 - 7/10)); Obviously Im wainting for "b=0.3" in the output but here's what I get: b=1 What?! Why this happens? If I make: System.out.println("b=" + (1-0.7)); I get the right result which is "b=0.3". What's going wrong here? Thanks!

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  • jQuery and margin: 0 auto

    - by Trevor Burnham
    So, this is a problem that's been asked before, but I'm hoping we can lay it to rest: I'm using jQuery 1.4. If I define the style #obj { margin: 0 auto; } and then do $('#obj').css('marginLeft'); the result is the computed value in pixels. Is there any way to tell whether those pixels come from the auto calculation or not, without parsing document.styleSheets?

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  • iPhone App is leaking memory; Instruments and Clang cannot find the leak

    - by Norbert
    Hi, i've developed an iPhone program which is kind of an image manipulation program: The user get an UIImagePickerController and selects an image. Then the program does some heavy calculating in a new thread (for responsiveness of the application). The thread has, of course, its own autorelease pool. When calculation is done, the seperated thread signals the main thread that the result can be presented. The app creates a new view controller, pushes it onto the navigation controller. In short: UIImagePickerController new thread (autorelease pool) does some heavy calculation with image data signal to main thread that it's done main thread creates view controller and pushes it onto navigation controller view controller presents image result My program works well, but if I dismiss the navigation controller's top view controller by tapping on the back button and repeat the whole process several times, my app crashes. But only on the device! Instruments cannot find any leaks (except for some minor ones which I don't feel responsible for: thread creation, NSCFString; overall about 10 kB). Even Clang static analyzer tells me that my could seems to be all right. I know that the UIImage class can cache images and objects returned from convenience methods get freed only whet their autorelease pool gets drained. But most of the time I work with CGImageRef and I use UIImage' alloc, init & release methods to free memory as soon as possible. Currently, I don't know how to isolate the problem. How would you approach this problem? Crash Log: Incident Identifier: F4C202C9-1338-48FC-80AD-46248E6C7154 CrashReporter Key: bb6f526d8b9bb680f25ea8e93bb071566ccf1776 OS Version: iPhone OS 3.1.1 (7C145) Date: 2009-09-26 14:18:57 +0200 Free pages: 372 Wired pages: 7754 Purgeable pages: 0 Largest process: _MY_APP_ Processes Name UUID Count resident pages _MY_APP_ <032690e5a9b396058418d183480a9ab3> 17766 (jettisoned) (active) debugserver <ec29691560aa0e2994f82f822181bffd> 107 syslog_relay <21e13fa2b777218bdb93982e23fb65d3> 62 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 notification_pro <8a7725017106a28b545fd13ed58bf98c> 64 afcd <98b45027fbb1350977bf1ca313dee527> 65 mediaserverd <eb8fe997a752407bea573cd3adf568d3> 319 ptpd <b17af9cf6c4ad16a557d6377378e8a1e> 142 syslogd <ec8a5bc4483638539fa1266363dee8b8> 68 BTServer <1bb74831f93b1d07c48fb46cc31c15da> 119 apsd <a639ba83e666cc1d539223923ce59581> 165 notifyd <2ed3a1166da84d8d8868e64d549cae9d> 101 CommCenter <f4239480a623fb1c35fa6c725f75b166> 161 SpringBoard <8919df8091fdfab94d9ae05f513c0ce5> 2681 (active) accessoryd <b66bcf6e77c3ee740c6a017f54226200> 90 configd <41e9d763e71dc0eda19b0afec1daee1d> 275 fairplayd <cdce5393153c3d69d23c05de1d492bd4> 108 mDNSResponder <f3ef7a6b24d4f203ed147f476385ec53> 103 lockdownd <6543492543ad16ff0707a46e512944ff> 297 launchd <73ce695fee09fc37dd70b1378af1c818> 71 **End**

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  • JQuery UI popup elements not positioning correctly

    - by Okku
    I am using both JQuery UI Dialog and JQuery UI autocomplete both have the same erroneous behavior when they popup, the position is always 0,0! I have tried some different position arguments when popping up the dialog but non seems to help. Any clues? Is this a bug in the position calculation in JQuery? Or is this some css bug? Versions are 1.4.2 and 1.8.0

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  • format result of dat calc in linq

    - by d daly
    Hi I have a calculation in a linq query, although it brings back the correct nuber of days, Im not sure how to better format it select new { time = (System.DateTime.Today - cs.date_case_opened), }; just now it shows eg 4:00:00:00 if the difference is 4 days, any ideas how i can present this better? thanks

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  • How does the elliptic-curve version of Diffie-Hellman cryptography work?

    - by cmaduro
    Does the Elliptic curve diffie hellman calculation look any different from the standard one defined here: /* * The basic Diffie-Hellman Key Agreement Equation * * The client initiates * A = g^a mod p * * Sends (g p A) to the server * * The server calculates B * B = g^b mod p * * Sends B back to client * * The client calculates K * K = B^a mod p * * The server calucaltes K * K = A^b mod p * */ Or is it just a specific way of selecting g, a, p and b? How are g,a,p and b selected anyway?

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  • regular expression to insert space beetween thousands and hundreds...

    - by pixelboy
    Regular expressions and I aren't quite good friends. So here's the really basic operation i'm trying to do using javascript (jQuery framwork that is). My calculation function return a number, unformated, and i'd like to separate thousands and hundreds by a white space ' '. I'm sure it's pretty easy for a regexp regular user... but for me... Thanks for the help.

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  • Is this ruby code thread safe?

    - by Ben K.
    Is this code threadsafe? It seems like it should be, because @myvar will never be assigned from multiple threads (assuming block completes in < 1s). But do I need to be worried about a situation where the second block is trying to read @myvar as it's being written? require 'rubygems' require 'eventmachine' @myvar = Time.now.to_i EventMachine.run do EventMachine.add_periodic_timer(1) do EventMachine.defer do @myvar = Time.now.to_i # some calculation and reassign end end EventMachine.add_periodic_timer(0.5) do puts @myvar end end

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  • How do I aggregate activerecord model data for a specific time period?

    - by gsiener
    I'm collecting data from a system every ~10s (this time difference varies due to communication time with networked devices). I'd like to calculate averages and sums of the stored values for this activerecord model on a daily basis. All records are stored in UTC. What's the correct way to sum and average values for, e.g., the previous day from midnight to midnight EST? I can do this in sql but don't know the "rails way" to make this calculation.

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  • Expose subset of a class - design question

    - by thanikkal
    Suppose i have a product class with about close to 100 properties. Now for some operations (Say tax calculation) i dont really need this bulky product type, rather only a subset that has price related properties. I am not sure if i should create different snap shots(class) of products that just has the properties that i am interested in. what would be the ideal approach so that i don't unnecessarily pass around unsought fluff? Thanks in advance.

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