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• Biased Random Number Generator

  - by cmptrer

  I am looking for a random number generator that can be biased. For instance, say I want a random number between 1-5, with the probability being: 1: Comes up 20% of the time 2: Comes up 10% of the time 3: Comes up 40% of the time 4: Comes up 25% of the time 5: Comes up 5% of the time Is there anything in the standard library, or other libraries out there that would do this? Alternatively, is there an efficient way to do this myself?

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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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• 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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• is Microsoft LC random generator patented?

  - by user396672

  I need a very simple pseudo random generator (no any specific quality requirements) and I found Microsoft's variant of LCG algorithm used for rand() C runtime library function fit my needs (gcc's one seems too complex). I found the algorithm here: http://rosettacode.org/wiki/Linear_congruential_generator#C However, I worry the algorithm (including its "magic numbers" i.e coefficients) may by patented or restricted for use in some another way. Is it allowed to use this algorithm without any licence or patent restrictions or not? I can't use library rand() because I need my results to be exactly reproducible on different platforms

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

  - by Sandro

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

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• Using system time directly to get random numbers

  - by Richard Mar.

  I had to return a random element from an array so I came up with this placeholder: return codes[(int) (System.currentTimeMillis() % codes.length - 1)]; Now than I think of it, I'm tempted to use it in real code. The Random() seeder uses system time as seed in most languages anyway, so why not use that time directly? As a bonus, I'm free from the worry of non-random lower bits of many RNGs. It this hack coming back to bite me? (The language is Java if that's relevant.)

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• Random enemy placement on a 2d grid

  - by Robb

  I want to place my items and enemies randomly (or as randomly as possible). At the moment I use XNA's Random class to generate a number between 800 for X and 600 for Y. It feels like enemies spawn more towards the top of the map than in the middle or bottom. I do not seed the generator, maybe that is something to consider. Are there other techniques described that can improve random enemy placement on a 2d grid?

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• Getting N random numbers that the sum is M

  - by marionmaiden

  Hello I want to get N random numbers that the sum of them is a value. For example, let's suppose I want 5 random numbers that their sum is 1 Then, a valid possibility is: 0.2 0.2 0.2 0.2 0.2 Other possibility is: 0.8 0.1 0.03 0.03 0.04 And so on. I need this for the creation of the matrix of belongings of the Fuzzy C-means.

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• Python: Random is barely random at all?

  - by orokusaki

  I did this to test the randomness of randint: >>> from random import randint >>> >>> uniques = [] >>> for i in range(4500): # You can see I optimistic. ... x = randint(500, 5000) ... if x in uniques: ... raise Exception('We duped ' + str(x) + ' at iteration number ' + str(i)) ... uniques.append(x) ... Traceback (most recent call last): File "(stdin)", line 4, in (module) Exception: 'We duped 4061 at iteration number 67 I tried about 10 times more and the best result I got was 121 iterations before a repeater. Is this the best sort of result you can get from the standard library?

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• Extended Events Code Generator v1.001 - A Quick Fix

  - by Adam Machanic

  If you're one of the estimated 3-5 people who've downloaded and are using my XE Code Generator , please note that version 1.000 has a small bug: text data (such as query text) larger than 8000 bytes is truncated. I've fixed this issue and am pleased to present version 1.001, attached to this post. Enjoy, and stay tuned for slightly more interesting enhancements! Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!...(read more)

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• Random World Generation

  - by Alex Larsen

  I'm making a game like minecraft (although a different idea) but I need a random world generator for a 1024 block wide and 256 block tall map. Basically so far I have a multidimensional array for each layer of blocks (a total of 262,114 blocks). This is the code I have now: Block[,] BlocksInMap = new Block[1024, 256]; public bool IsWorldGenerated = false; Random r = new Random(); private void RunThread() { for (int BH = 0; BH <= 256; BH++) { for (int BW = 0; BW <= 1024; BW++) { Block b = new Block(); if (BH >= 192) { } BlocksInMap[BW, BH] = b; } } IsWorldGenerated = true; } public void GenWorld() { new Thread(new ThreadStart(RunThread)).Start(); } I want to make tunnels and water but the way blocks are set is like this: Block MyBlock = new Block(); MyBlock.BlockType = Block.BlockTypes.Air; How would I manage to connect blocks so the land is not a bunch of floating dirt and stone?

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• Is C# Random Number Generator thread safe?

  - by noone

  can anyone tell me if the C# Random.Next() method is thread safe?

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• SQLAuthority News – Random Thoughts and Random Ideas

  - by pinaldave

  There are days when I keep on wondering about SQL, and even my life overall. Today is Saturday so I decided to write about SQL Server. Just like any other mornings, I woke up at 5 and opened my blog editor. I usually do not open Twitter or Facebook when I am planning to focus on my work, as they are little distractions for me. But today I opened my Twitter account and came across a very interesting quote from a friend: ‘Can I expect you to be different today?’ Well, I think it was very powerful quote for me to read first thing on a new day. This quote froze me for a while and made me think, “Do I really want to write about an SQL Server tip, or something different?”  After a little thinking, I’ve realized that for today I would go on and write something different. I am going to write about a few of the ideas and thoughts I had yesterday. After writing all these, I realized that if I am thinking so much in a day, and if I write a blog post of my random musing of the week or month, it can be so long (and boring). Here are some of my random thoughts I’d like to share with you: When the airplane lands, why does everybody get up and try to rush out when their luggage would be coming probably 20-30 minutes later? I really do not like this question when it was asked to me: “SQL Server is not using optimal index which I just created – how can I force it?” I am not going elaborate on this statement but you are allowed to in the comment section. Why do some people wish Good Morning even when they meet us after 4 PM? Can I optimize a query so much that it gives me a result before I execute it? Is it corruption when someone does their personal household work at office? The lane where I drive is always the slowest lane. Why waste time on correcting others when there are a lot of pending improvements for ourselves? If I have to get Tattoo, which SQL Server Execution Plan symbol should I get? Why do I reach office so early that the coffee machine is yet running its daily cleaning job? Why does every laptop have a ‘Page Up’ key at different locations on the keyboard? While I like color movies, I really appreciate black and white photographs. I do not appreciate statements like, “If I receive your books in PDF, I will spread it to many people to give you much greater exposure. So would you please send them to me ASAP?” Do not tell me, “Why does the database grow back after shrinking it every day?” I suggest you use “Search this blog” for the explanation. Petrol prices are currently at INR 74. I hope the rate remains there. Let me ask you the same question which started my day today:  “Can I expect you to be different today?” Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: About Me, PostADay, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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• How do I produce "enjoyably" random, as opposed to pseudo-random?

  - by Hilton Campbell

  I'm making a game which presents a number of different kinds of puzzles in sequence. I choose each puzzle with a pseudorandom number. For each puzzle, there are a number of variations. I choose the variation with another pseudorandom number. And so on. The thing is, while this produces near-true randomness, this isn't what the player really wants. The player typically wants what they perceive to be and identify as random, but only if it doesn't tend to repeat puzzles. So, not really random. Just unpredictable. Giving it some thought, I can imagine hacky ways of doing it. For example, temporarily eliminating the most recent N choices from the set of possibilities when selecting a new choice. Or assigning every choice an equal probability, reducing a choice's probability to zero on selection, and then increasing all probabilities slowly with each selection. I assume there's an established way of doing this, but I just don't know the terminology so I can't find it. Anyone know? Or has anyone solved this in a pleasing way?

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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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• Use of qsrand, random method that is not random

  - by Andy M

  Hey everyone, I'm having a strange problem here, and I can't manage to find a good explanation to it, so I thought of asking you guys : Consider the following method : int MathUtility::randomize(int Min, int Max) { qsrand(QTime::currentTime().msec()); if (Min > Max) { int Temp = Min; Min = Max; Max = Temp; } return ((rand()%(Max-Min+1))+Min); } I won't explain you gurus what this method actually does, I'll instead explain my problem : I realised that when I call this method in a loop, sometimes, I get the same random number over and over again... For example, this snippet... for(int i=0; i<10; ++i) { int Index = MathUtility::randomize(0, 1000); qDebug() << Index; } ...will produce something like : 567 567 567 567...etc... I realised too, that if I don't call qsrand everytime, but only once during my application's lifetime, it's working perfectly... My question : Why ?

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• Difference Procedural Generation and Random Generation

  - by U-No-Poo

  Today, I got into an argument about the term "procedural generation". My point was that its different from "classic" random generation in the way that procedural is based on a more mathematical, fractal based, algorithm leading to a more "realistic" distribution and the usual randomness of most languages are based on a pseudo-random-number generator, leading to an "unrealistic", in a way, ugly, distribution. This discussion was made with a heightmap in mind. The discussion left me somehow unconvinced about my own arguments though, so, is there more to it? Or am I the one who is, in fact, simply wrong?

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• Random number generation algorithm for human brains?

  - by Magnus Wolffelt

  Are you aware of, or have you devised, any practical, simple-to-learn "in-head" algorithms that let humans generate (somewhat "true") random numbers? By "in-head" I mean.. preferrably without any external tools or devices. Also, a high output (many random numbers per minute) is desirable. Asked this on SO but it didn't get much interest. Maybe this is better suited for programmers.. :) I'm genuinely curious about anything that people might have come up with on this problem.

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• Random Cache Expiry

  - by mahemoff

  I've been experimenting with random cache expiry times to avoid situations where an individual request forces multiple things to update at once. For example, a web page might include five different components. If each is set to time out in 30 minutes, the user will have a long wait time every 30 minutes. So instead, you set them all to a random time between 15 and 45 minutes to make it likely at most only one component will reload for any given page load. I'm trying to find any research or guidelines on this topic, e.g. optimal variance parameters. I do recall seeing one article about how Google (?) uses this technique, but can't locate it, and there doesn't seem to be much written about the topic.

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• Generate a random alphanumeric string in cocoa

  - by Ward

  Hey there, I know this can't be that hard. I've searched, but I can't seem to find a simple solution. I want to call a method, pass it the length and have it generate a random alphanumeric string. Any ideas? Are there any utility libraries out there that may have a bunch of these types of functions? Thanks, Howie

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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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