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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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  • 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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  • 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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  • Is code that terminates on a random condition guaranteed to terminate?

    - by Simon Campbell
    If I had a code which terminated based on if a random number generator returned a result (as follows), would it be 100% certain that the code would terminate if it was allowed to run forever. while (random(MAX_NUMBER) != 0): // random returns a random number between 0 and MAX_NUMBER print('Hello World') I am also interested in any distinctions between purely random and the deterministic random that computers generally use. Assume the seed is not able to be known in the case of the deterministic random. Naively it could be suggested that the code will exit, after all every number has some possibility and all of time for that possibility to be exercised. On the other hand it could be argued that there is the random chance it may not ever meet the exit condition-- the generator could generate 1 'randomly' until infinity. (I suppose one would question the validity of the random number generator if it was a deterministic generator returning only 1's 'randomly' though)

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  • c++ generate a good random seed for psudo random number generators

    - by posop
    I am trying to generate a good random seed for a psudo-random number generator. I thought I'd get the expert's opinions. let me know if this is a bad way of doing it or if there are much better ways. #include <iostream> #include <cstdlib> #include <fstream> #include <ctime> unsigned int good_seed() { unsigned int random_seed, random_seed_a, random_seed_b; std::ifstream file ("/dev/random", std::ios::binary); if (file.is_open()) { char * memblock; int size = sizeof(int); memblock = new char [size]; file.read (memblock, size); file.close(); random_seed_a = int(memblock); delete[] memblock; }// end if else { random_seed_a = 0; } random_seed_b = std::time(0); random_seed = random_seed_a xor random_seed_b; return random_seed; } // end good_seed()

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  • Server side random selection of players

    - by Ron
    Assuming I have a simple client-server game, where the server picks random players on a very frequent base, I was wondering what is the best way to select a random player (According to the following constraints): Solution must be high performance and highly scalable Random spread should be relatively even (meaning if I have 3 players and pick 99 times, they will all be picked 33 times more or less) Should only pick players who were active in the past X days (optional, but a big bonus) The actual DB or data model used to store players isn't an issue here, as we'll select the technology in accordance to our needs. However, high performance and scalability is (at the moment we have over 60,000 unique daily active players, and we plan on growing even more). Thanks!

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  • Make objects slide across the screen in random positions

    - by user3475907
    I want to make an object appear randomly at the right hand side of the screen and then slide across the screen and disapear at the left hand side. I am working with libgdx. I have this bit of code but it makes items fall from the top down. Please help. public EntityManager(int amount, OrthoCamera camera) { player = new Player(new Vector2(15, 230), new Vector2(0, 0), this, camera); for (int i = 0; i < amount; i++) { float x = MathUtils.random(0, MainGame.HEIGHT - TextureManager.ENEMY.getHeight()); float y = MathUtils.random(MainGame.WIDTH, MainGame.WIDTH * 10); float speed = MathUtils.random(2, 10); addEntity(new Enemy(new Vector2(x, y), new Vector2(-0, -speed))); }

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  • Is Unity's Random seeded automatically?

    - by Lohoris
    I seem to recall Unity's Random is automatically seeded; checking the documentation it doesn't say it outright, but a certain interpretation of their words might seem to imply it. The seed is normally set from some arbitrary value like the system clock before the random number functions are used. This prevents the same run of values from occurring each time a game is played and thus avoids predictable gameplay. However, it is sometimes useful to produce the same run of pseudo-random values on demand by setting the seed yourself. (emphasis added)

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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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  • generate random opacity number using math random

    - by TechyDude
    I am trying to generate a random number for the css opacity. This is what I tried so far. CSS .test{ position : absolute; width : 15px; height : 15px; border-radius:15px; background-color : black; }? Script $(function() { for (var i = 0; i < 300; i++) { $("<div>", { class: "test", css: { opacity: randomOpacity } }).appendTo("body"); } function randomOpacity() { var opac = 0; opac = Math.random() < 1; console.log(opac); } randomize(); });? The Fiddle

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