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• Custom listbox sorting

  - by Arcadian

  I need to sort the data contained within a number of listboxes. The user will be able to select between two different types of sorting using radio boxes, one of which is checked by default on form load. I have created the IF statements needed in order to test whether the checked condition is true for that radio button. but i need some help to create the custom sort algorithms. Each list with contain similar looking data, the only difference in the prefix with which each line starts. For example each line in the first listbox starts with the prefix "G30" and the second listbox will be "G31" and so on. There are 10 listboxes in total (G30-G39 in terms of prefixes). The first search algorithm has to sort the lines by the number order of the first 13 chars. Example: This is how the data looks before sorting G35:45:58:11 JG07 G35:45:20:41 JG01 G35:58:20:21 JG03 G35:66:22:20 JG05 G35:45:85:21 JG02 G35:64:56:11 JG03 G35:76:35:11 JG02 G35:77:97:12 JG03 G35:54:29:11 JG01 G35:55:51:20 JG01 G35:76:24:20 JG06 G35:76:55:11 JG01 and this is how it should look after sorting G35:45:20:41 JG01 G35:45:58:11 JG07 G35:45:85:21 JG02 G35:54:29:11 JG01 G35:55:51:20 JG01 G35:58:20:21 JG03 G35:64:56:11 JG03 G35:66:22:20 JG05 G35:76:24:20 JG06 G35:76:35:11 JG02 G35:76:55:11 JG01 G35:77:97:12 JG03 as you can see, the prefixes are the same. so it is sorted, lowest first, by the next pair integers, then the next pair and the next but not by the value after "JG". the second sort algorithm will ignore the first 13 chars and sort by order of the value after "JG", highest first. any help? theres some rep in it for you :) thanks in advance

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• Code Golf: Shortest Turing-complete interpreter.

  - by ilya n.

  I've just tried to create the smallest possible language interpreter. Would you like to join and try? Rules of the game: You should specify a programming language you're interpreting. If it's a language you invented, it should come with a list of commands in the comments. Your code should start with example program and data assigned to your code and data variables. Your code should end with output of your result. It's preferable that there are debug statements at every intermediate step. Your code should be runnable as written. You can assume that data are 0 and 1s (int, string or boolean, your choice) and output is a single bit. The language should be Turing-complete in the sense that for any algorithm written on a standard model, such as Turing machine, Markov chains, or similar of your choice, it's reasonably obvious (or explained) how to write a program that after being executred by your interpreter performs the algorithm. The length of the code is defined as the length of the code after removal of input part, output part, debug statements and non-necessary whitespaces. Please add the resulting code and its length to the post. You can't use functions that make compiler execute code for you, such as eval(), exec() or similar. This is a Community Wiki, meaning neither the question nor answers get the reputation points from votes. But vote anyway!

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• Varying performance of MSVC release exe

  - by Andrew

  Hello everyone, I am curious what could be the reason for highly varying performance of the same executable. Sometimes, I run it and it takes 20 seconds and sometimes it is 110. Source is compiled with MSVC in Release mode with standard options. The code is here: vector<double> Un; vector<double> Ucur; double *pUn, *pUcur; ... // time marching for (old_time=time-logfreq, time+=dt; time <= end_time; time+=dt) { for (i=1, j=Un.size()-1, pUn=&Un[1], pUcur=&Ucur[1]; i < j; ++i, ++pUn, ++pUcur) { *pUcur = (*pUn)*(1.0-0.5*alpha*( *(pUn+1) - *(pUn-1) )); } Ucur[0] = (Un[0])*(1.0-0.5*alpha*( Un[1] - Un[j] )); Ucur[j] = (Un[j])*(1.0-0.5*alpha*( Un[0] - Un[j-1] )); Un = Ucur; }

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• Dynamically created operators

  - by Gero

  I created a program using dev-cpp and wxwidgets which solves a puzzle. The user must fill the operations blocks and the results blocks, and the program will solve it. Im solving it using bruteforce, i generate all non repeated 9 length number combinations using a recursive algorithm. It does it pretty fast. Up to here all is great! But the problem is when my program operates depending the character on the blocks. Its extremely slow (it never gets the answer), because of the chars comparation against +, -, *, etc. Im doing a CASE. Is there some way or some programming language wich allows dinamic creation of operators? So i can define the operator ROW1COL2 to be a +, and the same way to all other operations. I leave a screenshot of the app, so its easier to understand how the puzzle works. http://www.imageshare.web.id/images/9gg5cev8vyokp8rhlot9.png PD: The algorithm works, i tryed it with a trivial puzzle, and solved it in a second.

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• Validation of viewstate MAC failed with nested master page

  - by just_name

  After I use a nested master page ,I face the following problem : Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. and sometimes Invalid related information [ViewStateException: Invalid viewstate. Client IP: 127.0.0.1 Port: User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20100101 Firefox/17.0 ViewState: 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...] [HttpException (0x80004005): Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.] System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) +116 System.Web.UI.ViewStateException.ThrowMacValidationError(Exception inner, String persistedState) +13 System.Web.UI.ObjectStateFormatter.Deserialize(String inputString) +220 System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter.Deserialize(String serializedState) +5 System.Web.UI.Util.DeserializeWithAssert(IStateFormatter formatter, String serializedState) +37 System.Web.UI.HiddenFieldPageStatePersister.Load() +202 System.Web.UI.Page.LoadPageStateFromPersistenceMedium() +106 System.Web.UI.Page.LoadAllState() +43 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3905 System.Web.UI.Page.ProcessRequest(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +262 System.Web.UI.Page.ProcessRequest() +79 System.Web.UI.Page.ProcessRequestWithNoAssert(HttpContext context) +21 System.Web.UI.Page.ProcessRequest(HttpContext context) +109 ASP.frm_items2_aspx.ProcessRequest(HttpContext context) in c:\Windows\Microsoft.NET\Framework\v2.0.50727\Temporary ASP.NET Files\root\a961040e\19f53d4c\App_Web_frm_items2.aspx.cdcab7d2.nkfrbsfi.0.cs:0 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +399 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +76 I use this Tool to fix this problem but in vain !! I don't know even the root cause of this problem !!

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• Could not determine the size of this expression.

  - by Søren

  Hi, I have resently started to use MATLAB Simulink, and my problem is that i can't implement an AMDF function, because simulink compiler cannot determine the lengths. Simulink errors: |--------------------------------------------------------------------------------------- Could not determine the size of this expression. Function 'Embedded MATLAB Function2' (#38.728.741), line 33, column 32: "1:flength-k+1" Errors occurred during parsing of Embedded MATLAB function 'Embedded MATLAB Function2'(#38) Embedded MATLAB Interface Error: Errors occurred during parsing of Embedded MATLAB function 'Embedded MATLAB Function2'(#38) . |--------------------------------------------------------------------------------------- MY CODE: |--------------------------------------------------------------------------------------- persistent sLength persistent fLength persistent amdf % Length of the frame flength = length(frame); % Pitch period is between 2.5 ms and 19.5 ms for LPC-10 algorithm % This because this algorithm assumes the frequencyspan is 50 and 400 Hz pH = ceil((1/min(fspan))*fs); if(pH flength) pH = flength; end; pL = ceil((1/max(fspan))*fs); if(pL <= 0 || pL = flength) pL = 0; end; sLength = pH - pL; % Normalize the frame frame = frame/max(max(abs(frame))); % Allocating memory for the calculation of the amdf %amdf = zeros(1,sLength); %%%%%%%% amdf = 0; % Calculating the AMDF with unbiased normalizing for k = (pL+1):pH amdf(k-pL) = sum(abs(frame(1:flength-k+1) - frame(k:flength)))/(flength-k+1); end; % Output of the AMDF if(min(amdf) < lvlThr) voiced = 1; else voiced = 0; end; % Output of the minimum of the amdf minAMDF = min(amdf); |---------------------------------------------------------------------------------------- HELP Kind regards Søren

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• Pthread Queue System

  - by Wallace

  Hi. I'm working on my assignment on pthreads. I'm new and never touched on pthreads before. Is there any sample codes or resources out there that anyone of you have, that might aid me in my assignment? Here are my assignment details. A pthread program about queue system: Write a C/C++ Pthread program for a Dental clinic’s queuing system that declares an array of integers of size N, where N is the maximum number of queue for the day. The pthread program uses two threads. Whenever there is a new dental appointment, the first thread (the creator) puts the queue numbers in the array, one after the other. The second thread (the remover) removes the queue numbers from the array whenever the dentist has seen the patient. This is done in a FIFO fashion (First In First Out). The algorithm of the creator is as follows: • If the array is not full then put a new number in it (the numbers start at 1 and are incremented by one each time, so the creator create queue number 1, 2, 3 etc.) • sleep for 1 to 10 seconds, randomly • repeat The algorithm of the remover is as follows: • If the array is not empty then remove its smallest queue number • sleep for 1 to 10 seconds, randomly • repeat You should use mutex locks to protect things that must be protected. Each thread should print on the screen what it is doing (eg: "number 13 is added into the queue", "number 7 is removed from the queue", etc.). The program should run forever. Any help will be appreciated. Thanks.

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• How to fix rotations in a Rubik's Cube?

  - by Eindbaas

  I'm trying to create a Rubik's Cube in Flash & Papervision and i'm really stuck here. I'm up to the point where i can rotate any plane of cubes once, but after that...it's messed up because all local coordinate systems are messy. I dont really know where to go from here, can anybody give any advice on what do do? I'm not looking for 'read about transformation matrices', i know i should (and i am doing that), but i'm not really sure what to look for. My idea is that, after each rotation, i should fix each coordinate system of each cube again, but i have no idea how. Any hints on what i want to achieve (in words), and why, are much appreciated. http://dl.dropbox.com/u/250155/rubik/main.html (you can press the K key once ;) )

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• Theory of formal languages - Automaton

  - by dader51

  Hi everybody ! I'm wondering about formal languages. I have a kind of parser : It reads à xml-like serialized tree structure and turn it into a multidimmensionnal array. I figured out that i need at least three variables to achieve the job : $tree = array(); // a new array $pTree = array(&$tree); // a new array which the first element points to $tree; $deep = 0; plus the one containing the sentence splitted into words. My point is on the similarities between the algorithm deing used and the differents kinds of automatons ( state machines turing machines stack ... ). The $words variable is the "tape" of the automaton, the test/conditions of the algorithm are transitions, $deep is the state and $tree is the output. I cannont figure what is $pTree. So the question is : which is the automaton I implictly use here, and to which formal languages family does it fit ? And what's about recursion ?

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• SSAS 2008/Excel 2007 - Can't see cube

  - by Brian

  I have created a cube in SSAS 2008. In BIDS and SSMS I can see it fine. However, I cannot connect through Excel. I have tried both Excel 2003 and Excel 2007. I must support both and neither work. I can see the database but the cubes do not show up. I created a dummy cube in the project using the wizard and deployed that to the same database. In Excel 2003, I can see and connect to the dummy cube. Excel 2007 can't even find the server/instance after adding this cube. I have used another computer and received the same results with Excel 2003. Does anyone have any suggestions? Thanks for any help you can give me. -Brian

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• How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: class Array def shuffle ret = dup j = length i = 0 while j > 1 r = i + rand(j) ret[i], ret[r] = ret[r], ret[i] i += 1 j -= 1 end ret end end (0..9).to_a.shuffle.each{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle is used to efficiently provide random ordering. My problem is that shuffle needs to operate on an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. Imagine replacing (0..9) with (0..99**99). This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do? [Edit1]: Why do I want to do this? I'm trying to exhaust the search space of a hash algorithm for a N-length input string looking for partial collisions. Each number I generate is equivalent to a unique input string, entropy and all. Basically, I'm "counting" using a custom alphabet. [Edit2]: This means that f(x) in the above examples is a method that generates a hash and compares it to a constant, target hash for partial collisions. I do not need to store the value of x after I call f(x) so memory should remain constant over time. [Edit3/4/5/6]: Further clarification/fixes.

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• Unexpected performance curve from CPython merge sort

  - by vkazanov

  I have implemented a naive merge sorting algorithm in Python. Algorithm and test code is below: import time import random import matplotlib.pyplot as plt import math from collections import deque def sort(unsorted): if len(unsorted) <= 1: return unsorted to_merge = deque(deque([elem]) for elem in unsorted) while len(to_merge) > 1: left = to_merge.popleft() right = to_merge.popleft() to_merge.append(merge(left, right)) return to_merge.pop() def merge(left, right): result = deque() while left or right: if left and right: elem = left.popleft() if left[0] > right[0] else right.popleft() elif not left and right: elem = right.popleft() elif not right and left: elem = left.popleft() result.append(elem) return result LOOP_COUNT = 100 START_N = 1 END_N = 1000 def test(fun, test_data): start = time.clock() for _ in xrange(LOOP_COUNT): fun(test_data) return time.clock() - start def run_test(): timings, elem_nums = [], [] test_data = random.sample(xrange(100000), END_N) for i in xrange(START_N, END_N): loop_test_data = test_data[:i] elapsed = test(sort, loop_test_data) timings.append(elapsed) elem_nums.append(len(loop_test_data)) print "%f s --- %d elems" % (elapsed, len(loop_test_data)) plt.plot(elem_nums, timings) plt.show() run_test() As much as I can see everything is OK and I should get a nice N*logN curve as a result. But the picture differs a bit: Things I've tried to investigate the issue: PyPy. The curve is ok. Disabled the GC using the gc module. Wrong guess. Debug output showed that it doesn't even run until the end of the test. Memory profiling using meliae - nothing special or suspicious. ` I had another implementation (a recursive one using the same merge function), it acts the similar way. The more full test cycles I create - the more "jumps" there are in the curve. So how can this behaviour be explained and - hopefully - fixed? UPD: changed lists to collections.deque UPD2: added the full test code UPD3: I use Python 2.7.1 on a Ubuntu 11.04 OS, using a quad-core 2Hz notebook. I tried to turn of most of all other processes: the number of spikes went down but at least one of them was still there.

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• Movies recommendation engine conceptual database design

  - by Supyxy

  I am working at an movie recommendations engine and i'm facing a DB design issue. My actual database looks like this: MOVIES [ID,TITLE] KEYWORDS_TABLE [ID,KEY_ID] - where ID is Foreign Key for MOVIES.id and KEY_ID is a key for a text keywords table This is not the entire DB, but i showed here what's important for my problem. I have about 50,000 movies and about 1,3 milion keywords correlations, and basically my algorithm consists in extracting all the who have the same keywords with a given movie, then ordering them by the number of keywords correlations. For example i looked for a movie similar to 'Cast away' and it returned 'Six days and six nights' because it had the most keywords correlations (4 keywords): Island Airplane crash Stranded Pilot The algorithm is based on more factors, but this one is the most important and the most difficult for the approach. Basically what i do now is getting all the movies that have at least one keyword similar to the given movie and then ordering them by other factors which are not important for a moment. There wouldn't be any problem if there weren't so many records, a query lasts in many cases up to 10-20 seconds and some of them return even over 5000 movies. Someone already helped me on here (thanks Mark Byers) with optimizing the query but that's not enough because it takes too longer SELECT DISTINCT M.title FROM keywords_table K1 JOIN keywords_table K2 ON K2.key_id = K1.key_id JOIN movies M ON K2.id = M.id WHERE K1.id = 4 So i thought it would be better if i pre-made those lists with movies recommendations for each movie, but i'm not sure how to design the tables.. whatever is it a good idea or how would you take this approach?

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• Are licenses relevant for small code snippets?

  - by Martin

  When I'm about to write a short algorithm, I first check in the base class library I'm using whether the algorithm is implemented in it. If not, I often do a quick google search to see if someone has done it before (which is the case, 19 times out of 20). Most of the time, I find the exact code I need. Sometimes it's clear what license applies to the source code, sometimes not. It may be GPL, LGPL, BSD or whatever. Sometimes people have posted a code snippet on some random forum which solves my problem. It's clear to me that I can't reuse the code (copy/paste it into my code) without caring about the license if the code is in some way substantial. What is not clear to me is whether I can copy a code snippet containing 5 lines or so without doing a license violation. Can I copy/paste a 5-line code snippet without caring about the license? What about one-liner? What about 10 lines? Where do I draw the line (no pun intended)? My second problem is that if I have found a 10-line code snippet which does exactly what I need, but feel that I cannot copy it because it's GPL-licensed and my software isn't, I have already memorized how to implement it so when I go around implementing the same functionality, my code is almost identical to the GPL licensed code I saw a few minutes ago. (In other words, the code was copied to my brain and my brain after that copied it into my source code).

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• C# Byte[] to Url Friendly String

  - by LorenVS

  Hello, I'm working on a quick captcha generator for a simple site I'm putting together, and I'm hoping to pass an encrypted key in the url of the page. I could probably do this as a query string parameter easy enough, but I'm hoping not too (just because nothing else runs off the query string)... My encryption code produces a byte[], which is then transformed using Convert.ToBase64String(byte[]) into a string. This string, however, is still not quite url friendly, as it can contain things like '/' and '='. Does anyone know of a better function in the .NET framework to convert a byte array to a url friendly string? I know all about System.Web.HttpUtility.UrlEncode() and its equivalents, however, they only work properly with query string parameters. If I url encode an '=' inside of the path, my web server brings back a 400 Bad Request error. Anyways, not a critical issue, but hoping someone can give me a nice solution **EDIT: Just to be absolutely sure exactly what I'm doing with the string, I figured I would supply a little more information. The byte[] that results from my encryption algorithm should be fed through some sort of algorithm to make it into a url friendly string. After this, it becomes the content of an XElement, which is then used as the source document for an XSLT transformation, and is used as a part of the href attribute for an anchor. I don't believe the xslt transformation is causing the issues, since what is coming through on the path appears to be an encoded query string parameter, but causes the HTTP 400 I've also tried HttpUtility.UrlPathEncode() on a base64 string, but that doesn't seem to do the trick either (I still end up with '/'s in my url)**

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• Calculating bounding box a certain distance away from a lat/long coordinate in Java

  - by Bryce Thomas

  Given a coordinate (lat, long), I am trying to calculate a square bounding box that is a given distance (e.g. 50km) away from the coordinate. So as input I have lat, long and distance and as output I would like two coordinates; one being the south-west (bottom-left) corner and one being the north-east (top-right) corner. I have seen a couple of answers on here that try to address this question in Python, but I am looking for a Java implementation in particular. Just to be clear, I intend on using the algorithm on Earth only and so I don't need to accommodate a variable radius. It doesn't have to be hugely accurate (+/-20% is fine) and it'll only be used to calculate bounding boxes over small distances (no more than 150km). So I'm happy to sacrifice some accuracy for an efficient algorithm. Any help is much appreciated. Edit: I should have been clearer, I really am after a square, not a circle. I understand that the distance between the center of a square and various points along the square's perimeter is not a constant value like it is with a circle. I guess what I mean is a square where if you draw a line from the center to any one of the four points on the perimeter that results in a line perpendicular to a side of the perimeter, then those 4 lines have the same length.

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• Compressibility Example

  - by user285726

  From my algorithms textbook: The annual county horse race is bringing in three thoroughbreds who have never competed against one another. Excited, you study their past 200 races and summarize these as prob- ability distributions over four outcomes: first (“first place”), second, third, and other. Outcome Aurora Whirlwind Phantasm 0.15 0.30 0.20 first 0.10 0.05 0.30 second 0.70 0.25 0.30 third 0.05 0.40 0.20 other Which horse is the most predictable? One quantitative approach to this question is to look at compressibility. Write down the history of each horse as a string of 200 values (first, second, third, other). The total number of bits needed to encode these track- record strings can then be computed using Huffman’s algorithm. This works out to 290 bits for Aurora, 380 for Whirlwind, and 420 for Phantasm (check it!). Aurora has the shortest encoding and is therefore in a strong sense the most predictable. How did they get 420 for Phantasm? I keep getting 400 bytes, as so: Combine first, other = 0.4, combine second, third = 0.6. End up with 2 bits encoding each position. Is there something I've misunderstood about the Huffman encoding algorithm? Textbook available here: http://www.cs.berkeley.edu/~vazirani/algorithms.html (page 156).

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• Generate a set of strings with maximum edit distance

  - by Kevin Jacobs

  Problem 1: I'd like to generate a set of n strings of fixed length m from alphabet s such that the minimum Levenshtein distance (edit distance) between any two strings is greater than some constant c. Obviously, I can use randomization methods (e.g., a genetic algorithm), but was hoping that this may be a well-studied problem in computer science or mathematics with some informative literature and an efficient algorithm or three. Problem 2: Same as above except that adjacent characters cannot repeat; the i'th character in each string may not be equal to the i+1'th character. E.g., 'CAT', 'AGA' and 'TAG' are allowed, 'GAA', 'AAT', and 'AAA' are not. Background: The basis for this problem is bioinformatic and involves designing unique DNA tags that can be attached to biologically derived DNA fragments and then sequenced using a fancy second generation sequencer. The goal is to be able to recognize each tag, allowing for random insertion, deletion, and substitution errors. The specific DNA sequencing technology has a relatively low error rate per base (~1%), but is less precise when a single base is repeated 2 or more times (motivating the additional constraints imposed in problem 2).

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• Converting currencies via intermediate currencies.

  - by chillitom

  class FxRate { string Base { get; set; } string Target { get; set; } double Rate { get; set; } } private IList<FxRate> rates = new List<FxRate> { new FxRate {Base = "EUR", Target = "USD", Rate = 1.3668}, new FxRate {Base = "GBP", Target = "USD", Rate = 1.5039}, new FxRate {Base = "USD", Target = "CHF", Rate = 1.0694}, new FxRate {Base = "CHF", Target = "SEK", Rate = 8.12} // ... }; Given a large yet incomplete list of exchange rates where all currencies appear at least once (either as a target or base currency): What algorithm would I use to be able to derive rates for exchanges that aren't directly listed? I'm looking for a general purpose algorithm of the form: public double Rate(string baseCode, string targetCode, double currency) { return ... } In the example above a derived rate would be GBP-CHF or EUR-SEK (which would require using the conversions for EUR-USD, USD-CHF, CHF-SEK) Whilst I know how to do the conversions by hand I'm looking for a tidy way (perhaps using LINQ) to perform these derived conversions perhaps involving multiple currency hops, what's the nicest way to go about this?

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• Divide a path into N sections using Java or PostgreSQL/PostGIS

  - by Guido

  Imagine a GPS tracking system that is following the position of several objects. The points are stored in a database (PostgreSQL + PostGIS). Each path is composed by a different number of points. That is the reason why, in order to compare a pair of paths, I need to divide every path in a set of 100 points. Do you know any PostGIS function that already implement this algorithm? I've not been able to find it. If not, I'd like to solve it using Java. In this case I'd like to know an efficient and easy to implement algorithm to divide a path into N points. The most simple example could be to divide this path into three points: position 1 : x=1, y=2 position 2 : x=1, y=3 And the result should be: position 1 : x=1, y=2 (starting point) position 2 : x=5, y=2.5 position 3 : x=9, y=3 (end point) Edit: By 'compare a pair of paths' I mean to calculate the distance between two paths. I plan to divide each path in 100 points, and sum the euclidean distance between each one of these points as the distance between the two paths.

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• Quickly determine if a number is prime in Python for numbers < 1 billion

  - by Frór

  Hi, My current algorithm to check the primality of numbers in python is way to slow for numbers between 10 million and 1 billion. I want it to be improved knowing that I will never get numbers bigger than 1 billion. The context is that I can't get an implementation that is quick enough for solving problem 60 of project Euler: I'm getting the answer to the problem in 75 seconds where I need it in 60 seconds. http://projecteuler.net/index.php?section=problems&id=60 I have very few memory at my disposal so I can't store all the prime numbers below 1 billion. I'm currently using the standard trial division tuned with 6k±1. Is there anything better than this? Do I already need to get the Rabin-Miller method for numbers that are this large. primes_under_100 = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97] def isprime(n): if n <= 100: return n in primes_under_100 if n % 2 == 0 or n % 3 == 0: return False for f in range(5, int(n ** .5), 6): if n % f == 0 or n % (f + 2) == 0: return False return True How can I improve this algorithm?

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• Truncate portions of a string to limit the whole string's length in Ruby

  - by Horace Loeb

  Suppose you want to generate dynamic page titles that look like this: "It was all a dream, I used to read word up magazine" from "Juicy" by The Notorious B.I.G I.e., "LYRICS" from "SONG_NAME" by ARTIST However, your title can only be 69 characters total and this template will sometimes generate titles that are longer. One strategy for solving this problem is to truncate the entire string to 69 characters. However, a better approach is to truncate the less important parts of the string first. I.e., your algorithm might look something like this: Truncate the lyrics until the entire string is <= 69 characters If you still need to truncate, truncate the artist name until the entire string is <= 69 characters If you still need to truncate, truncate the song name until the entire string is <= 69 characters If all else fails, truncate the entire string to 69 characters Ideally the algorithm would also limit the amount each part of the string could be truncated. E.g., step 1 would really be "Truncate the lyrics to a minimum of 10 characters until the entire string is <= 69 characters" Since this is such a common situation, I was wondering if someone has a library or code snippet that can take care of it.

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• Import a Collada model doesn't align to pixels

  - by Dan Friedman

  Assume I have a model that is simply a cube. (It is more complicated than a cube, but for the purposes of this discussion, we will simplify.) So when I am in Sketchup, the cube is Xmm by Xmm by Xmm, where X is an integer. I then export the a Collada file and subsequently load that into threejs. Now if I look at the geometry bounding box, the values are floats, not integers. So now assume I am putting cubes next to each other with a small space in between say 1 pixel. Because screens can't draw half pixels, sometimes I see one pixel and sometimes I see two, which causes a lack of uniformity. I think I can resolve this satisfactorily if I can somehow get the imported model to have integer dimensions. I have full access to all parts of the model starting with Sketchup, so any point in the process is fair game. Is it possible? Thanks.

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• finding ALL cycles in a huge sparse matrix

  - by Andy

  Hi there, First of all I'm quite a Java beginner, so I'm not sure if this is even possible! Basically I have a huge (3+million) data source of relational data (i.e. A is friends with B+C+D, B is friends with D+G+Z (but not A - i.e. unmutual) etc.) and I want to find every cycle within this (not necessarily connected) directed graph. I've found this thread (http://stackoverflow.com/questions/546655/finding-all-cycles-in-graph/549402#549402) which has pointed me to Donald Johnson's (elementary) cycle-finding algorithm which, superficially at least, looks like it'll do what I'm after (I'm going to try when I'm back at work on Tuesday - thought it wouldn't hurt to ask in the meanwhile!). I had a quick scan through the code of the Java implementation of Johnson's algorithm (in that thread) and it looks like a matrix of relations is the first step, so I guess my questions are: a) Is Java capable of handling a 3+million*3+million matrix? (was planning on representing A-friends-with-B by a binary sparse matrix) b) Do I need to find every connected subgraph as my first problem, or will cycle-finding algorithms handle disjoint data? c) Is this actually an appropriate solution for the problem? My understanding of "elementary" cycles is that in the graph below, rather than picking out A-B-C-D-E-F it'll pick out A-B-F, B-C-D etc. but that's not the end of the world given the task. E / \ D---F / \ / \ C---B---A d) If necessary, I can simplify the problem by enforcing mutuality in relations - i.e. A-friends-with-B <== B-friends-with-A, and if really necessary I can maybe cut down the data size, but realistically it is always going to be around the 1mil mark. z) Is this a P or NP task?! Am I biting off more than I can chew? Thanks all, any help appreciated! Andy

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• How can I compare market data feed sources for quality and latency improvement?

  - by yves Baumes

  I am in the very first stages of implementing a tool to compare 2 market data feed sources in order to prove the quality of new developed sources to my boss ( meaning there are no regressions, no missed updates, or wrong ), and to prove latencies improvement. So the tool I need must be able to check updates differences as well as to tell which source is the best (in term of latency). Concrectly, reference source could be Reuters while the other one is a Feed handler we develop internally. People warned me that updates might not arrive in the same order as Reuters implementation could differs totally from ours. Therefore a simple algorithm based on the fact that updates could arrive in the same order is likely not to work. My very first idea would be to use fingerprint to compare feed sources, as Shazaam application does to find the title of the tube you are submitting. Google told me it is based on FFT. And I was wondering if signal processing theory could behaves well with market access applications. I wanted to know your own experience in that field, is that possible to develop a quite accurate algorithm to meet the needs? What was your own idea? What do you think about fingerprint based comparison?

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