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  • Finding Cities within 'X' Kilometers (or Miles)

    - by Mike Curry
    This may or may not be clear, leave me a comment if I am off base, or you need more information. Perhaps there is a solution out there already for what I want in PHP. I am looking for a function that will add or subtract a distance from a longitude OR latitude value. Reason: I have a database with all Latitudes and Longitudes in it and want to form a query to extract all cities within X kilometers (or miles). My query would look something like this... Select * From Cities Where (Longitude > X1 and Longitude < X2) And (Latitude > Y1 and Latitude < Y2) Where X1 = Longitude - (distance) Where X2 = Longitude + (distance) Where Y1 = Latitude - (distance) Where Y2 = Latitude + (distance) I am working in PHP, with a MySql Database. Open to any suggestions also! :)

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  • Negative numbers, arrays javascript!

    - by zizzamia
    I was implementing a routing algorithm in javascript, but when I assign a negative one variable in the array gives me this error: invalid array length. var node = new Array() node[0] = new Array(6,7) node[1] = new Array(5,-4,8) node[2] = new Array(-2) //Here, invalid array length I do not know how to resolve this error.

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  • open source gossip-based membership protocol?

    - by Aaron
    I am looking for a library which I can plug into a distributed application which implements any gossip-based membership protocol. Such a library would allow me to send/receive membership lists, merge received membership lists, etc... Even better would be if the library implemented a protocol with performance O(logn) performance guarantees. Does anyone know of any open source library like this? It doesn't need to meet all of the aforementioned requirements; even something partially implemented would be helpful.

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  • sampling integers uniformly efficiently in python using numpy/scipy

    - by user248237
    I have a problem where depending on the result of a random coin flip, I have to sample a random starting position from a string. If the sampling of this random position is uniform over the string, I thought of two approaches to do it: one using multinomial from numpy.random, the other using the simple randint function of Python standard lib. I tested this as follows: from numpy import * from numpy.random import multinomial from random import randint import time def use_multinomial(length, num_points): probs = ones(length)/float(length) for n in range(num_points): result = multinomial(1, probs) def use_rand(length, num_points): for n in range(num_points): rand(1, length) def main(): length = 1700 num_points = 50000 t1 = time.time() use_multinomial(length, num_points) t2 = time.time() print "Multinomial took: %s seconds" %(t2 - t1) t1 = time.time() use_rand(length, num_points) t2 = time.time() print "Rand took: %s seconds" %(t2 - t1) if __name__ == '__main__': main() The output is: Multinomial took: 6.58072400093 seconds Rand took: 2.35189199448 seconds it seems like randint is faster, but it still seems very slow to me. Is there a vectorized way to get this to be much faster, using numpy or scipy? thanks.

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  • Ruby on Rails - Currency : commas causing an issue.

    - by easement
    Looking on SO, I see that the preferred way to currency using RoR is using decimal(8,2) and to output them using number_to_currency(); I can get my numbers out of the DB, but I'm having issues on getting them in. Inside my update action I have the following line: if @non_labor_expense.update_attributes(params[:non_labor_expense]) puts YAML::dump(params) The dump of params shows the correct value. xx,yyy.zz , but what gets stored in the DB is only xx.00 What do I need to do in order to take into account that there may be commas and a user may not enter .zz (the cents). Some regex and for comma? how would you handle the decimal if it were .2 versus .20 . There has to be a builtin or at least a better way. My Migration (I don't know if this helps): class ChangeExpenseToDec < ActiveRecord::Migration def self.up change_column :non_labor_expenses, :amount, :decimal, :precision => 8, :scale => 2 end def self.down change_column :non_labor_expenses, :amount, :integer end end

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  • Are there any languages that are dynamically typed but do not allow weak typing?

    - by Maulrus
    For example, adding a (previously undeclared) int and a string in pseudocode: x = 1; y = "2"; x + y = z; I've seen strongly typed languages that would not allow adding the two types, but those are also statically typed, so it's impossible to have a situation like above. On the other hand, I've seen weakly typed languages that allow the above and are statically typed. Are there any languages that are dynamically typed but are also strongly typed as well, so that the piece of code above would not be valid?

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  • Opengl Coordinate System

    - by praveen
    Say I am using an Identity Matrix for my modelViewTransformation Matrix on an Open GL ES2.0 program. The Co-ordinate system in this case is the canonical opengl co-ordinate system which extends from (-1,-1,-1) to (1,,1,1). My question is, is this coordinate system right-handed or left-handed? A broader question: Is there a document with OpenGL which can list all the mathematical conventions followed by the API?

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  • Efficiently generate a 16-character, alphanumeric string

    - by ensnare
    I'm looking for a very quick way to generate an alphanumeric unique id for a primary key in a table. Would something like this work? def genKey(): hash = hashlib.md5(RANDOM_NUMBER).digest().encode("base64") alnum_hash = re.sub(r'[^a-zA-Z0-9]', "", hash) return alnum_hash[:16] What would be a good way to generate random numbers? If I base it on microtime, I have to account for the possibility of several calls of genKey() at the same time from different instances. Or is there a better way to do all this? Thanks.

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  • Decoding relationship between two numbers?

    - by Nimbuz
    Is there any way (or calculator) to determine the relationship between two numbers. For example on one the temporary event ID cards, the Unique ID is 20309825 but the barcode when decoded reads 8336902052. What could be the relationship between these numbers, if any? Thanks in advance for your help!

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  • is rand() is perdicatable in C++

    - by singh
    Hi When i run below program i always get same values each time..Is rand is not a true random function. int main() { while(1) { getch(); cout<<rand()<<endl; } } In each run i am getting below values. 41 18467 6334 26500 19169 15724 ......

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  • Is rand() predictable in C++

    - by singh
    When I run the below program I always get the same values each time. Is rand not a true random function? int main() { while(1) { getch(); cout<<rand()<<endl; } } In each run I am getting the below values. 41 18467 6334 26500 19169 15724 ......

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  • Enhancing an 'ORDER BY' clause to judge condition by more than 1 integer

    - by Yvonne
    Hi folks, I have some PHP code which allows me to sort a column into ascending and descending order (upon click of a table row title), which is good. It works perfectly for my D.O.B colum (with date/time field type), but not for a quantity column. For example, I have quantites of 10, 50, 100, 30 and another 100. The order seems to be only appreciating the 1st integer, so my sorting of the column ends up in this order: 10, 100, 100, 30, 50... and 50, 30, 100, 100, 10. This is obviously incorrect as 100 is bigger than 50, therefore both 100 values should appear at the end surely? It seems to me that 100 is only being taken into account as having the '1' value, then it appears before 10 because the system recognises it has another 0. Is this normal to happen? Is there any way I can solve this problem? Thanks for any help. P.S. I can show code if necessary, but would like to know if this is a common issue by default.

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  • Ubuntu Linux main utilities

    - by Harry
    I've never used Ubuntu Linux before, but I am researching about the main system tools that are included, e.g. Windows has Disk Cleanup, Disk Defrag... but what does Ubuntu Linux have. I need to know what the main five utilities that are included on Ubuntu Linux and what do they do.

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  • Arbitrary-precision arithmetic Explanation

    - by TT
    I'm trying to learn C and have come across the inability to work with REALLY big numbers (i.e., 100 digits, 1000 digits, etc.). I am aware that there exist libraries to do this, but I want to attempt to implement it myself. I just want to know if anyone has or can provide a very detailed, dumbed down explanation of arbitrary-precision arithmetic. Thanks!

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  • Best way to get a reasonably random key for MYSQL records

    - by Steve N
    Hi there, I need to generate a reasonably random unique key for a table. It should be something like a GUID for MYSQL. I've tried UUID, but it looks like only the first few characters are actually random- the rest are the same every time I insert them. Essentially, it is desirable for this key field to be very difficult to guess, even if you already have one known value in the column. What is the best way to do this, and how should I set up the field data type to store the value efficiently? Thank you, Steve

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  • How to receive packets on the MCU's serial port?

    - by itisravi
    Hello, Consider this code running on my microcontroller unit(MCU): while(1){ do_stuff; if(packet_from_PC) send_data_via_gpio(new_packet); //send via general purpose i/o pins else send_data_via_gpio(default_packet); do_other_stuff; } The MCU is also interfaced to a PC via a UART.Whenever the PC sends data to the MCU, the *new_packet* is sent, otherwise the *default_packet* is sent.Each packet can be 5 or more bytes with a pre defined packet structure. My question is: 1.Should i receive the entire packet from PC using inside the UART interrut service routine (ISR)? In this case, i have to implement a state machine inside the ISR to assemble the packet (which can be lengthy with if-else or switch-case blocks). 2.Detect a REQUEST command (one byte)from the PC in my ISR set a flag, diable UART interrupt alone and form the packet in my while(1) loop by polling the UART?

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  • How much time should it take to find the sum of all prime numbers less than 2 million?

    - by Shahensha
    I was trying to solve this Project Euler Question. I implemented the sieve of euler as a helper class in java. It works pretty well for the small numbers. But when I input 2 million as the limit it doesn't return the answer. I use Netbeans IDE. I waited for a lot many hours once, but it still didn't print the answer. When I stopped running the code, it gave the following result Java Result: 2147483647 BUILD SUCCESSFUL (total time: 2,097 minutes 43 seconds) This answer is incorrect. Even after waiting for so much time, this isn't correct. While the same code returns correct answers for smaller limits. Sieve of euler has a very simple algo given at the botton of this page. My implementation is this: package support; import java.util.ArrayList; import java.util.List; /** * * @author admin */ public class SieveOfEuler { int upperLimit; List<Integer> primeNumbers; public SieveOfEuler(int upperLimit){ this.upperLimit = upperLimit; primeNumbers = new ArrayList<Integer>(); for(int i = 2 ; i <= upperLimit ; i++) primeNumbers.add(i); generatePrimes(); } private void generatePrimes(){ int currentPrimeIndex = 0; int currentPrime = 2; while(currentPrime <= Math.sqrt(upperLimit)){ ArrayList<Integer> toBeRemoved = new ArrayList<Integer>(); for(int i = currentPrimeIndex ; i < primeNumbers.size() ; i++){ int multiplier = primeNumbers.get(i); toBeRemoved.add(currentPrime * multiplier); } for(Integer i : toBeRemoved){ primeNumbers.remove(i); } currentPrimeIndex++; currentPrime = primeNumbers.get(currentPrimeIndex); } } public List getPrimes(){ return primeNumbers; } public void displayPrimes(){ for(double i : primeNumbers) System.out.println(i); } } I am perplexed! My questions is 1) Why is it taking so much time? Is there something wrong in what I am doing? Please suggest ways for improving my coding style, if you find something wrong.

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  • How to use a class's type as the type argument for an inherited collection property in C#

    - by Edelweiss Peimann
    I am trying to create a representation of various types of card that inherit from a generic card class and which all contain references to their owning decks. I tried re-declaring them, as suggested here, but it still won't convert to the specific card type. The code I currently have is as such: public class Deck<T> : List<T> where T : Card { void Shuffle() { throw new NotImplementedException("Shuffle not yet implemented."); } } public class Card { public Deck<Card> OwningDeck { get; set; } } public class FooCard : Card { public Deck<FooCard> OwningDeck { get { return (Deck<FooCard>)base.OwningDeck; } set { OwningDeck = value; } } } The compile-time error I am getting: Error 2 Cannot convert type 'Game.Cards.Deck' to 'Game.Cards.Deck' And a warning suggesting I use a new operator to specify that the hiding is intentional. Would doing so be a violation of convention? Is there a better way? My question to stackoverflow is this: Can what I am trying to do be done elegantly in the .NET type system? If so, can some examples be provided?

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  • Get countries within range of LAT/LONG coordinates

    - by ptrn
    Trouble! I'm looking for a way to find the countries within a given range of LAT/LONG coordinates. E.g.: When viewing a place in Africa in Google Maps, I get out which countries that are in my current view. This is a bit ambitious, and I think the main problem will be dealing with accuracy of the needed polygons. The accuracy of these don't need to be all that great, the borders can probably be tens of miles off, or even more. This will be needed for the entire world.

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  • Detect numbers and process them ?

    - by Madhup
    Hi, I am trying to detect the numbers written on a grid and then process them using the iPhone camera. What i have found till yet are some good examples like: http://blog.damiles.com/?p=93 http://cmgresearch.blogspot.com/2010/01/augmented-reality-on-iphone-how-to_01.html Although I am able to draw the numbers on the overlay view to a good extent but still not able to detect what these numbers are. What I don't wanna do is to go through the whole AI process: training the system, providing the system whole set of values and then process them, because this is so much troublesome for me as well for the performance of my application. So guys having any idea or work arround for this please help. Thanks, Madhup

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  • Function Returning Negative Value

    - by Geowil
    I still have not run it through enough tests however for some reason, using certain non-negative values, this function will sometimes pass back a negative value. I have done a lot of manual testing in calculator with different values but I have yet to have it display this same behavior. I was wondering if someone would take a look at see if I am missing something. float calcPop(int popRand1, int popRand2, int popRand3, float pERand, float pSRand) { return ((((((23000 * popRand1) * popRand2) * pERand) * pSRand) * popRand3) / 8); } The variables are all contain randomly generated values: popRand1: between 1 and 30 popRand2: between 10 and 30 popRand3: between 50 and 100 pSRand: between 1 and 1000 pERand: between 1.0f and 5500.0f which is then multiplied by 0.001f before being passed to the function above Edit: Alright so after following the execution a bit more closely it is not the fault of this function directly. It produces an infinitely positive float which then flips negative when I use this code later on: pPMax = (int)pPStore; pPStore is a float that holds popCalc's return. So the question now is, how do I stop the formula from doing this? Testing even with very high values in Calculator has never displayed this behavior. Is there something in how the compiler processes the order of operations that is causing this or are my values simply just going too high? If the later I could just increase the division to 16 I think.

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  • Fastest Way to generate 1,000,000+ random numbers in python

    - by Sandro
    I am currently writing an app in python that needs to generate large amount of random numbers, FAST. Currently I have a scheme going that uses numpy to generate all of the numbers in a giant batch (about ~500,000 at a time). While this seems to be faster than python's implementation. I still need it to go faster. Any ideas? I'm open to writing it in C and embedding it in the program or doing w/e it takes. Constraints on the random numbers: A Set of numbers 7 numbers that can all have different bounds: eg: [0-X1, 0-X2, 0-X3, 0-X4, 0-X5, 0-X6, 0-X7] Currently I am generating a list of 7 numbers with random values from [0-1) then multiplying by [X1..X7] A Set of 13 numbers that all add up to 1 Currently just generating 13 numbers then dividing by their sum Any ideas? Would pre calculating these numbers and storing them in a file make this faster? Thanks!

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