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  • Random number generation

    - by Chandan Shetty SP
    I am using below code to generate random numbers in range... int randomNumberWithinRange(int min,int max) { int snowSize = 0; do { snowSize = rand()%max; } while( snowSize < min || snowSize > max ); return snowSize; } for(int i = 0; i < 10 ; i++) NSlog("@"%d",\t", randomNumberWithinRange(1,100)); If I quit my application and restart, same set of numbers are generated. How to generate different set of random numbers for every launching.

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  • Gamma Distribution in Boost

    - by Kamchatka
    Hello, I'm trying to use the Gamma distribution from boost::math but it looks like it isn't possible to use it with boost::variate_generator. Could someone confirm that? Or is there a way to use it. I discovered that there is a boost::gamma_distribution undocumented that could probably be used too but it only allows to choose the alpha parameter from the distribution and not the beta. Thanks!

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  • how to make a name from random numbers?

    - by blood
    my program makes a random name that could have a-z this code makes a 16 char name but :( my code wont make the name and idk why :( can anyone show me what's wrong with this? char name[16]; void make_random_name() { byte loop = -1; for(;;) { loop++; srand((unsigned)time(0)); int random_integer; random_integer = (rand()%10)+1; switch(random_integer) { case '1': name[loop] = 'A'; break; case '2': name[loop] = 'B'; break; case '3': name[loop] = 'C'; break; case '4': name[loop] = 'D'; break; case '5': name[loop] = 'E'; break; case '6': name[loop] = 'F'; break; case '7': name[loop] = 'G'; break; case '8': name[loop] = 'Z'; break; case '9': name[loop] = 'H'; break; } cout << name << "\n"; if(loop > 15) { break; } } }

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  • form a number using consecutive numbers

    - by Mahesh
    Hi, I was puzzled with one of the question in Microsoft interview which is as given below: A function should accept a range( 3 - 21 ) and it should print all the consecutive numbers combination's to form each number as given below: 3=1+2 5=2+3 6=1+2+3 7=3+4 9=4+5 10=1+2+3+4 11=5+6 13=6+7 15=1+2+3+4+5 17=7+8 19=8+9 21=10+11 21=1+2+3+4+5+6 could you please help me in forming this sequence in C#? Thanks, Mahesh

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  • Generate n-dimensional random numbers in Python

    - by Magsol
    I'm trying to generate random numbers from a gaussian distribution. Python has the very useful random.gauss() method, but this is only a one-dimensional random variable. How could I programmatically generate random numbers from this distribution in n-dimensions? For example, in two dimensions, the return value of this method is essentially distance from the mean, so I would still need (x,y) coordinates to determine an actual data point. I suppose I could generate two more random numbers, but I'm not sure how to set up the constraints. I appreciate any insights. Thanks!

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  • How does this C# asp.net random password code work?

    - by quakkels
    Hello all, I'm new to .NET and C# and I'm trying to figure out how this code works: public static string CreateRandomPassword(int PasswordLength) { String _allowedChars = "abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNOPQRSTUVWXYZ23456789"; Byte[] randomBytes = new Byte[PasswordLength]; RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider(); rng.GetBytes(randomBytes); char[] chars = new char[PasswordLength]; int allowedCharCount = _allowedChars.Length; for(int i = 0;i<PasswordLength;i++) { /// /// I don't understand how this line works: /// chars[i] = _allowedChars[(int)randomBytes[i] % allowedCharCount]; } return new string(chars); } I think I've got a pretty good handle on most of this. I haven't been able to understand the following line: chars[i] = _allowedChars[(int)randomBytes[i] % allowedCharCount]; I understand that the code generates random binary numbers and uses those random numbers in the for loop to select a character from the _allowedChars string. What I don't get is why this code uses the modulous operator (%) to get the _allowedChars index value. Thanks for any help

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  • How to shuffle pairs

    - by Jessy
    How to shuffle the elements in the pairs? The program below, generate all possible pairs and later shuffle the pairs. e.g. possible pairs before shuffle is ab,ac,ae,af..etc shuffled to ac,ae,af,ab...etc How to make it not only shuffled in pairs but within the elements in the pair itself? e.g. instead of ab, ac, how can I make ba, ac ? String[] pictureFile = {"a.jpg","b.jpg","c.jpg","d.jpg","e.jpg","f.jpg","g.jpg"}; List <String> pic1= Arrays.asList(pictureFile); ... ListGenerator pic2= new ListGenerator(pic1); ArrayList<ArrayList<Integer>> pic2= new ArrayList<ArrayList<Integer>>(); public class ListGenerator { public ListGenerator(List<String> pic1) { int size = pic1.size(); // create a list of all possible combinations for(int i = 0 ; i < size ; i++) { for(int j = (i+1) ; j < size ; j++) { ArrayList<Integer> temp = new ArrayList<Integer>(); temp.add(i); temp.add(j); pic2.add(temp); } } Collections.shuffle(pic2); } //This method return the shuffled list public ArrayList<ArrayList<Integer>> getList() { return pic2; } }

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  • Synchronizing thread communication?

    - by Roger Alsing
    Just for the heck of it I'm trying to emulate how JRuby generators work using threads in C#. Also, I'm fully aware that C# haas built in support for yield return, I'm just toying around a bit. I guess it's some sort of poor mans coroutines by keeping multiple callstacks alive using threads. (even though none of the callstacks should execute at the same time) The idea is like this: The consumer thread requests a value The worker thread provides a value and yields back to the consumer thread Repeat untill worker thread is done So, what would be the correct way of doing the following? //example class Program { static void Main(string[] args) { ThreadedEnumerator<string> enumerator = new ThreadedEnumerator<string>(); enumerator.Init(() => { for (int i = 1; i < 100; i++) { enumerator.Yield(i.ToString()); } }); foreach (var item in enumerator) { Console.WriteLine(item); }; Console.ReadLine(); } } //naive threaded enumerator public class ThreadedEnumerator<T> : IEnumerator<T>, IEnumerable<T> { private Thread enumeratorThread; private T current; private bool hasMore = true; private bool isStarted = false; AutoResetEvent enumeratorEvent = new AutoResetEvent(false); AutoResetEvent consumerEvent = new AutoResetEvent(false); public void Yield(T item) { //wait for consumer to request a value consumerEvent.WaitOne(); //assign the value current = item; //signal that we have yielded the requested enumeratorEvent.Set(); } public void Init(Action userAction) { Action WrappedAction = () => { userAction(); consumerEvent.WaitOne(); enumeratorEvent.Set(); hasMore = false; }; ThreadStart ts = new ThreadStart(WrappedAction); enumeratorThread = new Thread(ts); enumeratorThread.IsBackground = true; isStarted = false; } public T Current { get { return current; } } public void Dispose() { enumeratorThread.Abort(); } object System.Collections.IEnumerator.Current { get { return Current; } } public bool MoveNext() { if (!isStarted) { isStarted = true; enumeratorThread.Start(); } //signal that we are ready to receive a value consumerEvent.Set(); //wait for the enumerator to yield enumeratorEvent.WaitOne(); return hasMore; } public void Reset() { throw new NotImplementedException(); } public IEnumerator<T> GetEnumerator() { return this; } System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { return this; } } Ideas?

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  • libnet that properly calculates checksum on IPV6

    - by VeaEm
    I have recently started playing around with libnet and using it to generate IPV6 packets. I am very new at programming, however, I am quite happy with the library. I have one problem with it though. It seems that libnet currently does not have the ability to properly calculate checksums on IPV6 packets. Being so new to programming, I am not yet capable of fixing this problem (although I am learning, so that one day I can). I am curious, has anyone run across a version of the library that can do this properly? Thanks!

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  • Could a truly random number be generated using pings to psuedo-randomly selected IP addresses?

    - by _ande_turner_
    The question posed came about during a 2nd Year Comp Science lecture while discussing the impossibility of generating numbers in a deterministic computational device. This was the only suggestion which didn't depend on non-commodity-class hardware. Subsequently nobody would put their reputation on the line to argue definitively for or against it. Anyone care to make a stand for or against. If so, how about a mention as to a possible implementation?

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  • Generating easy-to-remember random identifiers

    - by Carl Seleborg
    Hi all, As all developers do, we constantly deal with some kind of identifiers as part of our daily work. Most of the time, it's about bugs or support tickets. Our software, upon detecting a bug, creates a package that has a name formatted from a timestamp and a version number, which is a cheap way of creating reasonably unique identifiers to avoid mixing packages up. Example: "Bug Report 20101214 174856 6.4b2". My brain just isn't that good at remembering numbers. What I would love to have is a simple way of generating alpha-numeric identifiers that are easy to remember. Examples would be "azil3", "ulmops", "fel2way", etc. I just made these up, but they are much easier to recognize when you see many of them at once. I know of algorithms that perform trigram analysis on text (say you feed them a whole book in German) and that can generate strings that look and feel like German words. This requires lots of data, though, and makes it slightly less suitable for embedding in an application just for this purpose. Do you know of anything else? Thanks! Carl

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  • Random Number on SQL without using NewID()

    - by Angel Escobedo
    Hello I want to generate a Unique Random number with out using the follow statement : Convert(int, (CHECKSUM(NEWID()))*100000) AS [ITEM] Cause when I use joins clauses on "from" it generates double registers by using NEWID() Im using SQL Server 2000 *PD : When I use Rand() it probably repeat on probability 1 of 100000000 but this is so criticall so it have to be 0% of probability to repeat a random value generated My Query with NewID() and result on SELECT statement is duplicated (x2) My QUery without NewID() and using Rand() on SELECT statement is single (x1) but the probability of repeat the random value generated is uncertainly but exists! Thanks!

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  • C++ random number from a set

    - by user69514
    Is it possible to print a random number in C++ from a set of numbers with ONE SINGLE statement? let's say the set is 2, 5, 22, 55, 332 i looked up rand, but I double it's possible to do in a single statement

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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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  • No Secure Random Number Generators Available in JDK

    - by rwbutler
    Hi, I am currently running JDK 6 on Windows 7 and have installed the Unlimited Strength Policy Files. I wrote a Java app some time ago which used to work but now fails, giving an error message indicating that the SHA1PRNG SecureRandom is not available. I have tried printing a list of cryptographic providers available on the platform and it would appear that there are no secure random number generators available - does anyone have any idea why this might be? Many thanks in advance for your help!

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  • Creating a Function in SQL Server with a Phone Number as a parameter and returns a Random Number

    - by Emer
    Hi Guys, I am hoping someone can help me here as google is not being as forthcoming as I would have liked. I am relatively new to SQL Server and so this is the first function I have set myself to do. The outline of the function is that it has a Phone number varchar(15) as a parameter, it checks that this number is a proper number, i.e. it is 8 digits long and contains only numbers. The main character I am trying to avoid is '+'. Good Number = 12345678 Bad Number = +12345678. Once the number is checked I would like to produce a random number for each phone number that is passed in. I have looked at substrings, the like operator, Rand(), left(), Right() in order to search through the number and then produce a random number. I understand that Rand() will produce the same random number unless alterations are done to it but right now it is about actually getting some working code. Any hints on this would be great or even point me towards some more documentation. I have read books online and they haven't helped me, maybe I am not looking in the right places. Here is a snippet of code I was working on the Rand declare @Phone Varchar (15) declare @Counter Varchar (1) declare @NewNumber Varchar(15) set @Phone = '12345678' set @Counter = len(@Phone) while @Counter > 0 begin select case when @Phone like '%[0-9]%' then cast(rand()*100000000 as int) else 'Bad Number' end set @counter = @counter - 1 end return Thanks for the help in advance Emer

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  • Did I implement clock drift properly?

    - by David Titarenco
    I couldn't find any clock drift RNG code for Windows anywhere so I attempted to implement it myself. I haven't run the numbers through ent or DIEHARD yet, and I'm just wondering if this is even remotely correct... void QueryRDTSC(__int64* tick) { __asm { xor eax, eax cpuid rdtsc mov edi, dword ptr tick mov dword ptr [edi], eax mov dword ptr [edi+4], edx } } __int64 clockDriftRNG() { __int64 CPU_start, CPU_end, OS_start, OS_end; // get CPU ticks -- uses RDTSC on the Processor QueryRDTSC(&CPU_start); Sleep(1); QueryRDTSC(&CPU_end); // get OS ticks -- uses the Motherboard clock QueryPerformanceCounter((LARGE_INTEGER*)&OS_start); Sleep(1); QueryPerformanceCounter((LARGE_INTEGER*)&OS_end); // CPU clock is ~1000x faster than mobo clock // return raw return ((CPU_end - CPU_start)/(OS_end - OS_start)); // or // return a random number from 0 to 9 // return ((CPU_end - CPU_start)/(OS_end - OS_start)%10); } If you're wondering why I Sleep(1), it's because if I don't, OS_end - OS_start returns 0 consistently (because of the bad timer resolution, I presume). Basically, (CPU_end - CPU_start)/(OS_end - OS_start) always returns around 1000 with a slight variation based on the entropy of CPU load, maybe temperature, quartz crystal vibration imperfections, etc. Anyway, the numbers have a pretty decent distribution, but this could be totally wrong. I have no idea.

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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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  • 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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  • 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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  • Generating random numbers in C

    - by moonstruckhorrors
    While searching for Tutorials on generating random numbers in C I found This Topic When I try to use the rand() function with parameters, I always get the random number generated 0. When I try to use the rand() function with parameters, I always get the value 41. And whenever I try to use arc4random() and random() functions, I get a LNK2019 error. Here's what I'm doing: #include <stdlib.h> int main() { int x; x = rand(6); printf("%d", x); } This code always generate 41. Where am I going wrong?? P.S. : I'm running Windows XP SP3 and using VS2010 Command Prompt as compiler. P.P.S. : Took me 15 minutes to learn how to format properly.

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  • Five unique, random numbers from a subset

    - by tau
    I know similar questions come up a lot and there's probably no definitive answer, but I want to generate five unique random numbers from a subset of numbers that is potentially infinite (maybe 0-20, or 0-1,000,000). The only catch is that I don't want to have to run while loops or fill an array. My current method is to simply generate five random numbers from a subset minus the last five numbers. If any of the numbers match each other, then they go to their respective place at the end of the subset. So if the fourth number matches any other number, it will bet set to the 4th from the last number. Does anyone have a method that is "random enough" and doesn't involve costly loops or arrays? Please keep in mind this a curiosity, not some mission-critical problem. I would appreciate it if everyone didn't post "why are you having this problem?" answers. I am just looking for ideas. Thanks a lot!

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