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  • Get a random subset from a set in F#

    - by Cay
    I am trying to think of an elegant way of getting a random subset from a set in F# Any thoughts on this? Perhaps this would work: say we have a set of 2x elements and we need to pick a subset of y elements. Then if we could generate an x sized bit random number that contains exactly y 2n powers we effectively have a random mask with y holes in it. We could keep generating new random numbers until we get the first one satisfying this constraint but is there a better way?

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  • Random generates same number in java

    - by user1613360
    This is my java code. import java.io.*; import java.util.*; import java.util.concurrent.TimeUnit; class search { private int numelem; private int[] input=new int[100]; public void setNumofelem() { System.out.println("Enter the total numebr of elements"); Scanner yz=new Scanner(System.in); numelem=yz.nextInt(); } public void randomnumber() throws Exception { int max=500,min=1,n=numelem; Random rand = new Random(); for (int j=0;j < n;j++) { input[j]=rand.nextInt(max)+1; } } public void printinput() { int b=numelem,t=0; while(true) if(b!=0) { System.out.print(" "+input[t]); b--; t++; } else break; } } public class mycode { public static void main(String args[]) throws Exception { search a=new search(); a.setNumofelem(); a.randomnumber(); a.printinput(); } } Now the function randomnumber() just returns the same number.The function executes perfectly if I execute it as a separate java program but fails miserably if I call it using an object.I have also tried the following variations but nothing works everything return the same number. Variation 1: public void randomnumber() throws Exception { int max=500,min=1,n=numelem; Random rand = new Random(); for (int j=0;j < n;j++) { TimeUnit.SECONDS.sleep(1); input[j]=rand.nextInt(max)+1; } } Variation 2: public void randomnumber() throws Exception { int max=500,min=1,n=numelem; Random rand = new Random(); for (int j=0;j < n;j++) { rand.setSeed(System.nanoTime()); input[j]=rand.nextInt(max)+1; } } Variation 3: public void randomnumber() throws Exception { int max=500,min=1,n=numelem; Random rand = new Random(); for (int j=0;j < n;j++) { TimeUnit.SECONDS.sleep(1); rand.setSeed(System.nanoTime()); input[j]=rand.nextInt(max)+1; } } Sample input/Output: Enter the number of elements: 5 23 23 23 23 23 23

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  • Repeating random variables in VBA

    - by Soo
    How can I use randomize and rnd to get a repeating list of random variables? By repeating list, I mean if you run a loop to get 10 random numbers, each random number in the list will be unique. In addition, if you were to run this sequence again, you would get the same 10 random numbers as before.

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  • create a random sequence, skip to any part of the sequence

    - by Michael Xu
    Hi everyone, In Linux. There is an srand() function, where you supply a seed and it will guarantee the same sequence of pseudorandom numbers in subsequent calls to the random() function afterwards. Lets say, I want to store this pseudo random sequence by remembering this seed value. Furthermore, let's say I want the 100 thousandth number in this pseudo random sequence later. One way, would be to supply the seed number using srand(), and then calling random() 100 thousand times, and remembering this number. Is there a better way of skipping all 99,999 other numbers in the pseudo random list and directly getting the 100 thousandth number in the list. thanks, m

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  • Noob Droid Question regarding random number

    - by Pete Herbert Penito
    Brand new to droid programming, but would love to learn as much as possible, so I finally got my emulator working correctly, I even got a hello world button to work, I'm attempting to make this button display a random number, I've googled this and came up with this code: Random generator = new Random(); int n = generator.nextInt(n); I fixed the Random function by including some Random java utility. I'm assuming this code above goes in the .java file of the project, so my button code looks as follows (tested and works): PopUpText.makeText(v.getContext(), "Hello World", PopUpText.LENGTH_LONG).show(); I figured I could replace "Hello World" with n to display the number in the box, however the following error is stopping the compile: The local variable n may not have been initialized Any ideas why this is happening? Any advice would be hugely appreciated.

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  • Could random.randint(1,10) ever return 11?

    - by Tim Pietzcker
    When researching for this question and reading the sourcecode in random.py, I started wondering whether randrange and randint really behave as "advertised". I am very much inclined to believe so, but the way I read it, randrange is essentially implemented as start + int(random.random()*(stop-start)) (assuming integer values for start and stop), so randrange(1, 10) should return a random number between 1 and 9. randint(start, stop) is calling randrange(start, stop+1), thereby returning a number between 1 and 10. My question is now: If random() were ever to return 1.0, then randint(1,10) would return 11, wouldn't it?

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  • only return random number when it is unique

    - by phil
    My brain is melting today and i cannot think how to do this simple bit of code. numberList is a string of numbers seperated by commas like '2, 34, 10' etc.. when i request a random number i need to check if the string has the number, if it does i want to keep requesting a random number until the random number is definitely not in the string. i cant think what kind of loop i would do to get this to work: Random r = new Random(); public int RandomPos(int max) { int i; do { i = r.Next(max) + 1; } while (!numberList.Contains(i.ToString())); return i; }

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  • Choosing random numbers efficiently

    - by Frederik Wordenskjold
    I have a method, which uses random samples to approximate a calculation. This method is called millions of times, so its very important that the process of choosing the random numbers is efficient. I'm not sure how fast javas Random().nextInt really are, but my program does not seem to benefit as much as I would like it too. When choosing the random numbers, I do the following (in semi pseudo-code): // Repeat this 300000 times Set set = new Set(); while(set.length != 5) set.add(randomNumber(MIN,MAX)); Now, this obviously has a bad worst-case running time, as the random-function in theory can add duplicated numbers for an eternity, thus staying in the while-loop forever. However, the numbers are chosen from {0..45}, so a duplicated value is for the most part unlikely. When I use the above method, its only 40% faster than my other method, which does not approximate, but yields the correct result. This is ran ~ 1 million times, so I was expecting this new method to be at least 50% faster. Do you have any suggestions for a faster method? Or maybe you know of a more efficient way of generation a set of random numbers.

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  • Two different seeds producing the same "random" sequence

    - by Ruud Lenders
    Maybe there is a very logic explanation for this, but I just can't seem to understand why the seeds 0 and 2,147,483,647 produce the same "random" sequence, using .NET's Random Class (System). Quick code example: ushort len = 8; Random r0 = new Random(0), r1 = new Random(1), r2 = new Random(int.MaxValue); //2,147,483,647 byte[] b0 = new byte[len], b1 = new byte[len], b2 = new byte[len]; r0.NextBytes(b0); r1.NextBytes(b1); r2.NextBytes(b2); for (int i = 0; i < len; i++) { System.Diagnostics.Debug.WriteLine("{0}\t\t{1}\t\t{2}", b0[i], b1[i], b2[i]); } Console.ReadLine(); Output: 26 70 26 12 208 12 70 134 76 111 130 111 93 64 93 117 151 115 228 228 228 216 163 216 As you can see, the first and the third sequence are the same. Can someone please explain this to me?

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  • Same random numbers from instantiated class

    - by user1797202
    I'm learning C# and created a class within my program that holds a random number generator: class RandomNumberGenerator { Random RNG = new Random(); // A bunch of methods that use random numbers are in here } Inside this class are a few methods that use the RNG. Data gets sent here from other parts of the program, gets processed, then gets returned. One of the methods does the following: // Method works something like this int Value1 = RNG.Next(x, y); int Value2 = RNG.Next(x, y); int Value3 = RNG.Next(x, y); The x, y values are to be sent here from another class. So, I have to create an instance of the RandomNumberGenerator within that class so I can call its methods and pass the x and y values to it. class DoStuff { RandomNumberGenerator Randomizer = new RandomNumberGenerator // Here I call a bunch of Randomizer methods that give me values I need } The problem in the above method is that I get the same numbers every time for all three values. I'm not sure if it's because they're so close together and Randomizer's seed value hasn't had time to change or if I'm doing something wrong when I create a new instance of the RandomNumberGenerator class. I've gone through a bunch of answers on here already and typically problems like this are due to people creating many new Random objects when they run methods (thus setting the seed for all of them to the same value), but the only new Random object I create is within the RandomNumberGenerator class. I then instantiate that once within the other class so I can pass it data and use its methods. Why is this happening and how would I fix this?

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  • How Hacker Can Access VPS CentOS 6 content?

    - by user2118559
    Just want to understand. Please, correct mistakes and write advices Hacker can access to VPS: 1. Through (using) console terminal, for example, using PuTTY. To access, hacker need to know port number, username and password. Port number hacker can know scanning open ports and try to login. The only way to login as I understand need to know username and password. To block (make more difficult) port scanning, need to use iptables configure /etc/sysconfig/iptables. I followed this https://www.digitalocean.com/community/articles/how-to-setup-a-basic-ip-tables-configuration-on-centos-6 tutorial and got *nat :PREROUTING ACCEPT [87:4524] :POSTROUTING ACCEPT [77:4713] :OUTPUT ACCEPT [77:4713] COMMIT *mangle :PREROUTING ACCEPT [2358:200388] :INPUT ACCEPT [2358:200388] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [2638:477779] :POSTROUTING ACCEPT [2638:477779] COMMIT *filter :INPUT DROP [1:40] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [339:56132] -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG NONE -j DROP -A INPUT -p tcp -m tcp ! --tcp-flags FIN,SYN,RST,ACK SYN -m state --state NEW -j DROP -A INPUT -p tcp -m tcp --tcp-flags FIN,SYN,RST,PSH,ACK,URG FIN,SYN,RST,PSH,ACK,URG -j DROP -A INPUT -i lo -j ACCEPT -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT -A INPUT -p tcp -m tcp --dport 110 -j ACCEPT -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT -A INPUT -s 11.111.11.111/32 -p tcp -m tcp --dport 22 -j ACCEPT -A INPUT -p tcp -m tcp --dport 21 -j ACCEPT -A INPUT -s 11.111.11.111/32 -p tcp -m tcp --dport 21 -j ACCEPT COMMIT Regarding ports that need to be opened. If does not use ssl, then seems must leave open port 80 for website. Then for ssh (default 22) and for ftp (default 21). And set ip address, from which can connect. So if hacker uses other ip address, he can not access even knowing username and password? Regarding emails not sure. If I send email, using Gmail (Send mail as: (Use Gmail to send from your other email addresses)), then port 25 not necessary. For incoming emails at dynadot.com I use Email Forwarding. Does it mean that emails “does not arrive to VPS” (before arriving to VPS, emails are forwarded, for example to Gmail)? If emails does not arrive to VPS, then seems port 110 also not necessary. If use only ssl, must open port 443 and close port 80. Do not understand regarding port 3306 In PuTTY with /bin/netstat -lnp see Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name tcp 0 0 0.0.0.0:3306 0.0.0.0:* LISTEN 992/mysqld As understand it is for mysql. But does not remember that I have opened such port (may be when installed mysql, the port is opened automatically?). Mysql is installed on the same server, where all other content. Need to understand regarding port 3306 2. Also hacker may be able access console terminal through VPS hosting provider Control Panel (serial console emergency access). As understand only using console terminal (PuTTY, etc.) can make “global” changes (changes that can not modify with ftp). 3. Hacker can access to my VPS exploiting some hole in my php code and uploading, for example, Trojan. Unfortunately, faced situation that VPS was hacked. As understand it was because I used ZPanel. On VPS ( \etc\zpanel\panel\bin) ) found one php file, that was identified as Trojan by some virus scanners (at virustotal.com). Experimented with the file on local computer (wamp). And appears that hacker can see all content of VPS, rename, delete, upload etc. From my opinion, if in PuTTY use command like chattr +i /etc/php.ini then hacker could not be able to modify php.ini. Is there any other way to get into VPS?

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  • What makes you look like a bad developer (ie a hacker) [on hold]

    - by user134583
    This comes from a lot of people about me, so I have to look at myself. So I would wonder what make one a bad developer (ie a hacker). These are a few things about me I used IDE intensively, all features, you name it: auto-completion, refactoring, quick fixes, open type, view hierarchy, API documentation, etcc When I deal with writing code for a project in domain I am not used to (I can't have fluency in this, this is new), I only have a very rough high level ideas. I don't use the standard modeling diagrams for early detail planning. Unorthodox diagrams that I invented when I need to draw the design in details. I don't use UML or similar, I find them not enough. I divide the sorts of diagram I drew into 3 types. Very high level diagrams which probably can be understood by almost anybody. Data entity diagram used for modeling data objects only (like ER diagrams and tree for inheritances and composition). Action diagrams for agents/classes and their interactions on data objects they contain. Constantly changing the interface (public methods) between interacting agents/classes if the need arises. I am more refrained when the interface and the module have matured Write initial concept code in a quick hackie way just so that the module works in the general cases so that I can play around with it. The module will be re-factored intensively after playing around so I could see more corner cases that I couldn't or (wouldn't want) anticipate before writing code. Using JUnit for integration-like test by using TestSuite class and ordering Unit test classes in the suite Using debugger almost anytime there is a problem instead of reading the code Constantly search on the internet for how to do some thing with some library that I haven't used a lot. So judgment, am I a bad developer? a hacker? Put in other words, to make sure this is not considered off-topic: - Is this bad practice to make your code too agile during incubating/prototyping phase of software development - Is it bad practice to use JUnit for integration testing, (I know there are other framework for integration testing, but those frameworks are for a specific products, not general)

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  • What's a good algorithm for a random, uneven distribution of a fixed amount of a resource?

    - by NickC
    Problem I have X, a positive integer, of some resource, R. There are N potential targets. I want to distribute all of R to the N targets in some "interesting" way. "Interesting" means: Some targets may not get any R. It should rarely be near even (with a majority of target getting near X/N of the resource). There should be at least a small chance of one target getting all of R. Bad solutions The naive approach would be to pick a random target and give one R to it and repeat X times. This would result in too even of an approach. The next idea is to pick a random number between 1 and X and give it to a random target. This results in too large of a number (at least X/2 on average) being given to one target. Question This algorithm will be used frequently and I want the distribution to be interesting and uneven so that the surprise doesn't wear off for users. Is there a good algorithm for something in between these two approaches, that fits the definition of interesting above?

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  • How Random is System.Guid.NewGuid()? (Take two)

    - by Vilx-
    Before you start marking this as a duplicate, read me out. The other question has a (most likely) incorrect accepted answer. I do not know how .NET generates its GUIDs, probably only Microsoft does, but there's a high chance it simply calls CoCreateGuid(). That function however is documented to be calling UuidCreate(). And the algorithms for creating an UUID are pretty well documented. Long story short, be as it may, it seems that System.Guid.NewGuid() indeed uses version 4 UUID generation algorithm, because all the GUIDs it generates matches the criteria (see for yourself, I tried a couple million GUIDs, they all matched). In other words, these GUIDs are almost random, except for a few known bits. This then again raises the question - how random IS this random? As every good little programmer knows, a pseudo-random number algorithm is only as random as its seed (aka entropy). So what is the seed for UuidCreate()? How ofter is the PRNG re-seeded? Is it cryptographically strong, or can I expect the same GUIDs to start pouring out if two computers accidentally call System.Guid.NewGuid() at the same time? And can the state of the PRNG be guessed if sufficiently many sequentially generated GUIDs are gathered?

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  • Apache2 random 403 error & info server busy logs on Ubuntu

    - by risyasin
    Hello, I have a strange situation with apache2. Meanless, random 403 errors. Any page (html, php etc.) normally working. but if i request repeatedly by pressing refresh button of browser. it interrupts & sends a 403 randomly. after a few seconds it works again. in the error log, i see client denied by server configuration. main error log of apache says [info] server seems busy, (you may need to increase StartServers, or Min/MaxSpareServers), spawning 8 children, there are 99 idle, and 137 total children my current values IfModule mpm_prefork_module StartServers 120 MinSpareServers 100 MaxSpareServers 200 MaxClients 256 MaxRequestsPerChild 500 /IfModule i've increased 10 by 10. from 20. but nothing solved. i've disabled KeepAlive. What may cause this problem ? thank you in advance. a fresh install Ubuntu server x86 8.04.4 Virtualmin from it's website (not from debian repositories). Linux 2.6.24-27-server #1 SMP i686 - Apache 2.2.8 Mpm prefork Virtualmin version 3.78.gpl GPL PHP Version 5.2.4-2ubuntu5.10 Loaded modules: core_module (static) log_config_module (static) logio_module (static) mpm_prefork_module (static) http_module (static) so_module (static) actions_module shared) alias_module (shared) auth_basic_module (shared) auth_digest_module (shared) uthn_file_module (shared) authz_default_module (shared) authz_groupfile_module (shared) uthz_host_module (shared) authz_user_module (shared) autoindex_module (shared) ache_module shared) cgi_module (shared) deflate_module (shared) dir_module (shared) env_module (shared) expires_module (shared) fcgid_module (shared) file_cache_module (shared) eaders_module (shared) mime_module (shared) mime_magic_module (shared) evasive20_module shared) negotiation_module (shared) php5_module (shared) rewrite_module (shared) etenvif_module (shared) ssl_module (shared) status_module (shared) Syntax OK

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  • module "random" not found when building .exe from IronPython 2.6 script

    - by Graham
    I am using SharpDevelop to build an executable from my IronPython script. The only hitch is that my script has the line import random which works fine when I run the script through ipy.exe, but when I attempt to build and run an exe from the script in SharpDevelop, I always get the message: IronPython.Runtime.Exceptions.ImportException: No module named random Why isn't SharpDevelop 'seeing' random? How can I make it see it?

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  • Reversible pseudo-random sequence generator

    - by user350651
    I would like some sort of method to create a fairly long sequence of random numbers that I can flip through backwards and forwards. Like a machine with "next" and "previous" buttons, that will give you random numbers. Something like 10-bit resolution (i.e. positive integers in a range from 0 to 1023) is enough, and a sequence of 100k numbers. It's for a simple game-type app, I don't need encryption-strength randomness or anything, but I want it to feel fairly random. I have a limited amount of memory available though, so I can't just generate a chunk of random data and go through it. I need to get the numbers in "interactive time" - I can easily spend a few ms thinking about the next number, but not comfortably much more than that. Eventually it will run on some sort of microcontroller, probably just an Arduino. I could do it with a simple linear congruential generator (LCG). Going forwards is simple, to go backwards I'd have to cache the most recent numbers and store some points at intervals so I can recreate the sequence from there. But maybe there IS some pseudo-random generator that allows you to go both forwards and forwards? It should be possible to hook up two linear feedback shift registers (LFSRs) to roll in different directions, no? Or maybe I can just get by with garbling the index number using a hash function of some sort? I'm going to try that first. Any other ideas?

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  • Best way to choose a random file from a directory in a shell script

    - by jhs
    What is the best way to choose a random file from a directory in a shell script? Here is my solution in Bash but I would be very interested for a more portable (non-GNU) version for use on Unix proper. dir='some/directory' file=`/bin/ls -1 "$dir" | sort --random-sort | head -1` path=`readlink --canonicalize "$dir/$file"` # Converts to full path echo "The randomly-selected file is: $path" Anybody have any other ideas? Edit: lhunath makes a good point about parsing ls. I guess it comes down to whether you want to be portable or not. If you have the GNU findutils and coreutils then you can do: find "$dir" -maxdepth 1 -mindepth 1 -type f -print0 \ | sort --zero-terminated --random-sort \ | sed 's/\d000.*//g/' Whew, that was fun! Also it matches my question better since I said "random file". Honsetly though, these days it's hard to imagine a Unix system deployed out there having GNU installed but not Perl 5.

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  • Join a single row in one table to n random rows in another

    - by Einar Egilsson
    Is it possible to make a join in SQL server that joins each row from table A to n random rows in another? For example, say I have a Customer table, a Product table and an Order table. I want to join each customer to 5 random products and insert these rows into the order table. (And each customer should be joined to 5 random rows of his own, I don't want all customers joining to the same 5 rows). Is this possible? I'm using SQL Server 2005 and it's fine if the solution is specific to that. This is a weird requirement but I'm basically making a small data generator to generate some random data.

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