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  • C: Random Number Generation - What (If Anything) Is Wrong With This

    - by raoulcousins
    For a simple simulation in C, I need to generate exponential random variables. I remember reading somewhere (but I can't find it now, and I don't remember why) that using the rand() function to generate random integers in a fixed range would generate non-uniformly distributed integers. Because of this, I'm wondering if this code might have a similar problem: //generate u ~ U[0,1] u = ( (double)rand() / ((double)(RAND_MAX)); //inverse of exponential CDF to get exponential random variable expon = -log(1-u) * mean; Thank you!

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  • Random Movement for multiple entities

    - by opiop65
    I have this code for a arraylist of entities. All the entities use the same random and so all of them move in the same direction. How can I change it so it generates a new random number for each entity? public void moveFemale() { for(int i = 0; i < 1000; i++){ random = rand.nextInt(99); } if (random >= 0 && random <= 25) { posX -= enemyWalkSpeed; // right } if (random >= 26 && random <= 50) { posX += enemyWalkSpeed; // left } if (random >= 51 && random <= 75) { posY -= enemyWalkSpeed; // up } if (random >= 76 && random <= 100) { posY += enemyWalkSpeed; // down } } Is this correct? public void moveFemale() { for (Female female: GameFrame.females){ female.lastChangedDirectionTime += elapsedTime; if (female.lastChangedDirectionTime >= CHANGE_DIRECTION_TIME) { female.lastChangedDirectionTime = 0; random = rand.nextInt(100); if (random >= 0 && random <= 25) { posX -= enemyWalkSpeed; // right } if (random >= 26 && random <= 50) { posX += enemyWalkSpeed; // left } if (random >= 51 && random <= 75) { posY -= enemyWalkSpeed; // up } if (random >= 76 && random <= 100) { posY += enemyWalkSpeed; // down } } } }

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  • Random Between: using random with the instance_create function in GML

    - by CLockeWork
    Hopefully this should be a simple one; I want to restrict the points that instances enter the screen from so they don't come in at the edges. In Game Maker I'm using the following code instance_create(random(room_width), random(-100) - 50, obj_enemy1); to create the instance off screen (create(x, y, ...)) At the moment I'm just using the room_width to define the max width for the random on x, but ideally I want to find a way of defining a max AND min width for the random. I can't figure out how to restrict the range on the x axis to between say 100 and 350. Any help would be appreciated. Cheers

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  • Text inside <p> shrinks on mobile devices while div does not [migrated]

    - by guisasso
    I asked this question on stack overflow, but didn't get any answers, so I'm trying here. Does anybody know whats happening here? I tested on opera, dolphin and the factory android browser. (although it seems now to be working on opera) The div doesn't change size, but the text somehow is shrunk to fit on part of a div. Anyway to prevent this? Just to be clear, I'm trying to achieve on the mobile browser the same look as the pc version. As the problem seems to be with the browsers, how can I force the text to take the full width of the div? I tried setting the p tag to 100% with no success. The div has to have that width and be aligned to the left of the page. On a Pc, as it should be: I shrunk the code as much as I could: <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" lang="en-us"> <head> <meta content="text/html; charset=utf-8" http-equiv="Content-Type" /> <meta content="" name="keywords" /> <meta content="" name="description" /> <title></title> </head> <body> <div style="width:1000px; margin-left:auto; margin-right:auto;" > <div style="float:left; width:758px; background-color:aqua;"> <p> Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text .<br /> <br /> Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text Random text .<br /> <br /> Random text Random text Random text Random text <a href="http://www.a.com/a.html"> Random text </a> Random text Random text . </p> </div> </div> </body> </html> Thanks.

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  • How can I make an even more random number in ActionScript 2.0

    - by Theo
    I write a piece of software that runs inside banner ads which generates millions of session IDs every day. For a long time I've known that the random number generator in Flash is't random enough to generate sufficiently unique IDs, so I've employed a number of tricks to get even more random numbers. However, in ActionScript 2.0 it's not easy, and I'm seeing more and more collisions, so I wonder if there is something I've overlooked. As far as I can tell the problem with Math.random() is that it's seeded by the system time, and when you have sufficient numbers of simultaneous attempts you're bound to see collisions. In ActionScript 3.0 I use the System.totalMemory, but there's no equivalent in ActionScript 2.0. AS3 also has Font.enumerateFonts, and a few other things that are different from system to system. On the server side I also add the IP address to the session ID, but even that isn't enough (for example, many large companies use a single proxy server and that means that thousands of people all have the same IP -- and since they tend to look at the same sites, with the same ads, roughly at the same time, there are many session ID collisions). What I need isn't something perfectly random, just something that is random enough to dilute the randomness I get from Math.random(). Think of it this way: there is a certain chance that two people will generate the same random number sequence using only Math.random(), but the chance of two people generating the same sequence and having, say, the exact same list of fonts is significantly lower. I cannot rely on having sufficient script access to use ExternalInterface to get hold of things like the user agent, or the URL of the page. I don't need suggestions of how to do it in AS3, or any other system, only AS2 -- using only what's available in the standard APIs. The best I've come up with so far is to use the list of microphones (Microphone.names), but I've also tried to make some fingerprinting using some of the properties in System.capabilities, I'm not sure how much randomness I can get out of that though so I'm not using that at the moment. I hope I've overlooked something.

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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 do functional languages handle random numbers?

    - by Electric Coffee
    What I mean about that is that in nearly every tutorial I've read about functional languages, is that one of the great things about functions, is that if you call a function with the same parameters twice, you'll always end up with the same result. How on earth do you then make a function that takes a seed as a parameter, and then returns a random number based on that seed? I mean this would seem to go against one of the things that are so good about functions, right? Or am I completely missing something here?

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  • How to obtain a random sub-datatable from another data table

    - by developerit
    Introduction In this article, I’ll show how to get a random subset of data from a DataTable. This is useful when you already have queries that are filtered correctly but returns all the rows. Analysis I came across this situation when I wanted to display a random tag cloud. I already had the query to get the keywords ordered by number of clicks and I wanted to created a tag cloud. Tags that are the most popular should have more chance to get picked and should be displayed larger than less popular ones. Implementation In this code snippet, there is everything you need. ' Min size, in pixel for the tag Private Const MIN_FONT_SIZE As Integer = 9 ' Max size, in pixel for the tag Private Const MAX_FONT_SIZE As Integer = 14 ' Basic function that retreives Tags from a DataBase Public Shared Function GetTags() As MediasTagsDataTable ' Simple call to the TableAdapter, to get the Tags ordered by number of clicks Dim dt As MediasTagsDataTable = taMediasTags.GetDataValide ' If the query returned no result, return an empty DataTable If dt Is Nothing OrElse dt.Rows.Count < 1 Then Return New MediasTagsDataTable End If ' Set the font-size of the group of data ' We are dividing our results into sub set, according to their number of clicks ' Example: 10 results -> [0,2] will get font size 9, [3,5] will get font size 10, [6,8] wil get 11, ... ' This is the number of elements in one group Dim groupLenth As Integer = CType(Math.Floor(dt.Rows.Count / (MAX_FONT_SIZE - MIN_FONT_SIZE)), Integer) ' Counter of elements in the same group Dim counter As Integer = 0 ' Counter of groups Dim groupCounter As Integer = 0 ' Loop througt the list For Each row As MediasTagsRow In dt ' Set the font-size in a custom column row.c_FontSize = MIN_FONT_SIZE + groupCounter ' Increment the counter counter += 1 ' If the group counter is less than the counter If groupLenth <= counter Then ' Start a new group counter = 0 groupCounter += 1 End If Next ' Return the new DataTable with font-size Return dt End Function ' Function that generate the random sub set Public Shared Function GetRandomSampleTags(ByVal KeyCount As Integer) As MediasTagsDataTable ' Get the data Dim dt As MediasTagsDataTable = GetTags() ' Create a new DataTable that will contains the random set Dim rep As MediasTagsDataTable = New MediasTagsDataTable ' Count the number of row in the new DataTable Dim count As Integer = 0 ' Random number generator Dim rand As New Random() While count < KeyCount Randomize() ' Pick a random row Dim r As Integer = rand.Next(0, dt.Rows.Count - 1) Dim tmpRow As MediasTagsRow = dt(r) ' Import it into the new DataTable rep.ImportRow(tmpRow) ' Remove it from the old one, to be sure not to pick it again dt.Rows.RemoveAt(r) ' Increment the counter count += 1 End While ' Return the new sub set Return rep End Function Pro’s This method is good because it doesn’t require much work to get it work fast. It is a good concept when you are working with small tables, let says less than 100 records. Con’s If you have more than 100 records, out of memory exception may occur since we are coping and duplicating rows. I would consider using a stored procedure instead.

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  • Generate a Strong Password using Mac OS X Lion’s Built-in Utility

    - by Usman
    You might’ve heard of the LinkedIn and last.fm security breaches that took place recently. Not to mention the thousands of websites that have been hacked till now. Nothing is invulnerable to hacking. And when something like that happens, passwords are leaked. Choosing a good password is essential. A good password generator can give you the best blend of alphanumeric and symbolic characters, making up a strong password. There are a variety of password generators out there, but not many people know that there’s one built right into Mac OS X Lion. Read on to see how you can generate a strong password without any third party application. To do this, open System Preferences. Click “Users & Groups”. How to Make Your Laptop Choose a Wired Connection Instead of Wireless HTG Explains: What Is Two-Factor Authentication and Should I Be Using It? HTG Explains: What Is Windows RT and What Does It Mean To Me?

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  • is there a such thing as a randomly accessible pseudo-random number generator? (preferably open-sour

    - by lucid
    first off, is there a such thing as a random access random number generator, where you could not only sequentially generate random numbers as we're all used to, assuming rand100() always generates a value from 0-100: for (int i=0;i<5;i++) print rand100() output: 14 75 36 22 67 but also randomly access any random value like: rand100(0) would output 14 as long as you didn't change the seed rand100(3) would always output 22 rand100(4) would always output 67 and so on... I've actually found an open-source generator algorithm that does this, but you cannot change the seed. I know that pseudorandomness is a complex field; I wouldn't know how to alter it to add that functionality. Is there a seedable random access random number generator, preferably open source? or is there a better term for this I can google for more information? if not, part 2 of my question would be, is there any reliably random open source conventional seedable pseudorandom number generator so I could port it to multiple platforms/languages while retaining a consistent sequence of values for each platform for any given seed?

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  • VB.NET - Removing a number from a random number generator

    - by Alex
    I am trying to create a lottery simulator. The lottery has 6 numbers, the number generated must be between 1 - 49 and cannot be in the next number generated. I have tried using the OR function but I'm not entirely sure if I am using it properly. Any help would be great. Thanks. Public Class Form1 Private Sub cmdRun_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdRun.Click 'Creates a new Random class in VB.NET Dim RandomClass As New Random() '#################################### Dim RandomNumber1 As Integer RandomNumber1 = RandomClass.Next(1, 49) 'Displays first number generated txtFirst.Text = (RandomNumber1) '#################################### Dim RandomNumber2 As Integer RandomNumber2 = RandomClass.Next(1, 49) If RandomNumber2 = RandomNumber1 Then RandomNumber2 = RandomClass.Next(1, 49) End If 'Displays second number generated txtSecond.Text = (RandomNumber2) '#################################### Dim RandomNumber3 As Integer RandomNumber3 = RandomClass.Next(1, 49) If RandomNumber3 = RandomNumber2 Or RandomNumber2 Then RandomNumber3 = RandomClass.Next(1, 49) End If 'Displays third number generated txtThird.Text = (RandomNumber3) '#################################### Dim RandomNumber4 As Integer RandomNumber4 = RandomClass.Next(1, 49) If RandomNumber4 = RandomNumber3 Or RandomNumber2 Or RandomNumber1 Then RandomNumber4 = RandomClass.Next(1, 49) End If 'Displays fourth number generated txtFourth.Text = (RandomNumber4) '#################################### Dim RandomNumber5 As Integer RandomNumber5 = RandomClass.Next(1, 49) If RandomNumber5 = RandomNumber4 Or RandomNumber3 Or RandomNumber2 Or RandomNumber1 Then RandomNumber5 = RandomClass.Next(1, 49) End If 'Displays fifth number generated txtFifth.Text = (RandomNumber5) '#################################### Dim RandomNumber6 As Integer RandomNumber6 = RandomClass.Next(1, 49) If RandomNumber6 = RandomNumber5, RandomNumber4, RandomNumber3, RandomNumber2, RandomNumber1 Then RandomNumber6 = RandomClass.Next(1, 49) End If 'Displays sixth number generated txtSixth.Text = (RandomNumber6) End Sub

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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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  • Random encounter not so random

    - by DoomStone
    Hello i am having some problems generating random numbers with C# Now i have this function. public Color getRandomColor() { Color1 = new Random().Next(new Random().Next(0, 100), new Random().Next(200, 255)); Color2 = new Random().Next(new Random().Next(0, 100), new Random().Next(200, 255)); Color3 = new Random().Next(new Random().Next(0, 100), new Random().Next(200, 255)); Color color = Color.FromArgb(Color1, Color2, Color3); Console.WriteLine("R: " + Color1 + " G: " + Color2 + " B: " + Color3 + " = " + color.Name); return color; } Now you might notice that there are ALOT of new Random() there, that is because i want to weed out the probability that it could be a same instance error. I now run this function 8 times, a couple of times. Now here are the out puts. R: 65 G: 65 B: 65 = ff414141 R: 242 G: 242 B: 242 = fff2f2f2 R: 205 G: 205 B: 205 = ffcdcdcd R: 40 G: 40 B: 40 = ff282828 R: 249 G: 249 B: 249 = fff9f9f9 R: 249 G: 249 B: 249 = fff9f9f9 R: 94 G: 94 B: 94 = ff5e5e5e R: 186 G: 186 B: 186 = ffbababa R: 142 G: 142 B: 142 = ff8e8e8e R: 190 G: 190 B: 190 = ffbebebe R: 19 G: 19 B: 19 = ff131313 R: 119 G: 119 B: 119 = ff777777 R: 119 G: 119 B: 119 = ff777777 R: 75 G: 75 B: 75 = ff4b4b4b R: 169 G: 169 B: 169 = ffa9a9a9 R: 127 G: 127 B: 127 = ff7f7f7f R: 73 G: 73 B: 73 = ff494949 R: 27 G: 27 B: 27 = ff1b1b1b R: 125 G: 125 B: 125 = ff7d7d7d R: 212 G: 212 B: 212 = ffd4d4d4 R: 174 G: 174 B: 174 = ffaeaeae R: 0 G: 0 B: 0 = ff000000 R: 0 G: 0 B: 0 = ff000000 R: 220 G: 220 B: 220 = ffdcdcdc As you can see this is not so random again, but why dose this happens? and how can i counter it?

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  • RANDOM Number Generation in C

    - by CVS-2600Hertz-wordpress-com
    Recently i have begun development of a simple game. It is improved version of an earlier version that i had developed. Large part of the game's success depends on Random number generation in different modes: MODE1 - Truly Random mode myRand(min,max,mode=1); Should return me a random integer b/w min & max. MODE2 - Pseudo Random : Token out of a bag mode myRand(min,max,mode=2); Should return me a random integer b/w min & max. Also should internally keep track of the values returned and must not return the same value again until all the other values are returned atleast once. MODE3 - Pseudo Random : Human mode myRand(min,max,mode=3); Should return me a random integer b/w min & max. The randomisation ought to be not purely mathematically random, rather random as user perceive it. How Humans see RANDOM. * Assume the code is time-critical (i.e. any performance optimisations are welcome) * Pseudo-code will do but an implementation in C is what i'm looking for. * Please keep it simple. A single function should be sufficient (thats what i'm looking for) Thank You

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  • Grabbing random object from ArrayList is not random.

    - by Isai
    I am creating a method where if you pass in a parameter of type Random, then it will return a random object. Here is basically what I am trying to do: public T choose(Random r) { int randomInt = r.nextInt(randomList.size()); // randomList is just a instance variable return randomList.get(randomInt); } The random list has this the following strings:[2, 2, 2, 1, 1, 1, 1, c, c, c, a, a, a, a] Then I made a driver with the following code for (int i = 0; i < 10; i++) { System.out.print(rndList.choose(rnd)); // rnd is initialized as a static Random variable } However my outputs are not coming out random. I used the debugger and found out that my choose method generates an integer that is relatively low, so it will always print out either 2's or 1's but never c's or a's. I can't figure out why this is happening and help would be greatly appreciated.

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  • Pseudo random numbers in php

    - by pg
    I have a function that outputs items in a different order depending on a random number. for example 1/2 of the time Popeye's and its will be #1 on the list and Taco Bell and its logo will be #2 and half the time the it will be the other way around. The problem is that when a user reloads or comes back to the page, the order is re-randomized. $Range here is the number of items in the db, so it's using a random number between 1 and the $range. $random = mt_rand(1,$range); for ($i = 0 ; $i < count($variants); $i++) { $random -= $variants[$i]['weight']; if ($random <= 0) { $chosenoffers[$tag] = $variants[$i]; break; } } I went to the beginning of the session and set this: if (!isset($_SESSION['rannum'])){ $_SESSION['rannum']=rand(1,100); } With the idea that I could replace the mt_rand in the function with some sort of pseudo random generator that used the same 1-100 random number as a seed throughout the session. That way i won't have to rewrite all the code that was already written. Am I barking up the wrong tree or is this a good idea?

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  • Can Java's random function be zero?

    - by ThirdD3gree
    Just out of curiosity, can Math.random() ever be zero? For example, if I were to have: while (true){ if (Math.random() == 0) return 1; } Would I ever actually get a return of one? There's also rounding error to consider because Math.random() returns a double. I ask because my CS professor stated that random() goes from 0 to 1 inclusive, and I always thought it was exclusive.

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  • Generate random coordinates from area outside of a rectangle?

    - by Rockmaninoff
    Hi all, I'm working on a simple tutorial, and I'd like to randomly generate the positions of the red and green boxes in the accompanying images anywhere inside the dark gray area, but not in the white area. Are there any particularly elegant algorithms to do this? There are some hackish ideas I have that are really simple (continue to generate while the coordinates are not outside the inside rectangle, etc.), but I was wondering if anyone had come up with some neat solutions. Thanks for any help!

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  • how random is Math.random() in java across different jvms or different machines

    - by user881480
    I have a large distributed program across many different physical servers, each program spawns many threads, each thread use Math.random() in its operations to draw a piece from many common resource pools. The goal is to utilize the pools evenly across all operations. Sometimes, it doesn't appear so random by looking at a snapshot on a resource pool to see which pieces it's getting at that instant (it might actually be, but it's hard to measure and find out for sure). Is there something that's better than Math.random() and performs just as good (not much worse at least)?

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  • .NET: will Random.Random operate differently inside a static method

    - by Craig Johnston
    I am having difficulty with the following code which is inside a static method of a non-static class. int iRand; int rand; rand = new Random((int)DateTime.Now.Ticks); iRand = rand.Next(50000); The iRand number, along with some other values, are being inserted into a new row of an Access MDB table via OLEDB. The iRand number is being inserted into a field that is part of the primary key, and the insert attempt is throwing the following exception even though the iRand number is supposed to be random: System.Data.OleDb.OleDbException: The changes you requested to the table were not successful because they would create duplicate values in the index, primary key, or relationship. Change the data in the field or fields that contain duplicate data, remove the index, or redefine the index to permit duplicate entries and try again. Could the fact the method is static be making the iRand number stay the same, for some reason?

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  • Probability Random Number Generator

    - by Excl
    Let's say I'm writing a simple luck game - each player presses Enter and the game assign him a random number between 1-6. Just like a cube. At the end of the game, the player with the highest number wins. Now, let's say I'm a cheater. I want to write the game so player #1 (which will be me) has a probability of 90% to get six, and 2% to get each of the rest numbers (1, 2, 3, 4, 5). So, how can I generate a number random, and set the probability for each number? Thanks.

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