Tagged Questions

Questions about random number generation and the properties of numbers so generated.

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4
votes
1answer
141 views

How do I randomly select 'k' positions in a list and shuffle their respective elements without effecting the other elements?

Imagine I have some list: listA = {"a","b","c","d","e","f","g","h","i","j"}; I'd like to randomly select k positions in the ...
1
vote
1answer
110 views

Generating a random sample of elements from a list that includes a subset of the list

Imagine I have a list: tList = {item1,item2,item3,item4,item5,item6,...}, and I'd like to take a random sample of numItems ...
1
vote
0answers
76 views

How do I keep a random value associated with a locator point as points are added?

I have a Manipulate to which I am adding and removing Locator points (one of which is different from the others, though that is ...
3
votes
1answer
182 views

Put random points into a specific 2D subregion

I want to cover a particular subregion of the x-y plane with a random distribution. As this particular region is not a circle I encounter some problems declaring the permitted zone where to put ...
1
vote
1answer
120 views

How to replace a list with the result list after each iteration [closed]

I have some initial values such as L1 list: L1={10,20,30,40,50}; I want to use the L1 ...
5
votes
3answers
522 views

Fast code to generate large random graph with fixed degree sequence

I'm trying to create a function so to generate large random graph with a fixed degree sequence $\{v_1,v_2,\dots,v_N\}$, where $N$ is the number of vertices in the graph. The Mathematica function that ...
0
votes
1answer
111 views

Index of iteration inside NestList [duplicate]

I have a list of RandomReal: delta = RandomReal[{-0.01, 0.01}, 1000] I want to add each element of the list to the ...
1
vote
3answers
180 views

How to update a list in a function in each iteration

There is a list with numbers 1 to 8 ( p1 ) and another list (j) which contains 4 numbers which shows different 4 positions of ...
1
vote
0answers
138 views

Monte Carlo integration with random numbers generated from a Gaussian distribution

I want to do numerical integration of some functions using the Monte Carlo method. The default setting for the Monte Carlo method is to use a uniform distribution as far as I know. How can I change ...
1
vote
3answers
194 views

How to replace identical positions in two different lists

Assume that I have two lists like : list1={1,2,3,4,5}; list2={a,b,c,d,e}; I want to replace some elements from list1 into ...
0
votes
1answer
52 views

How to put some values from a list into a function in a Do loop

I want to program a code in MATHEMATICA in order to calculate some values in different iteration. For example, assume this list: list={1,2,3,4,5} Now assume that ...
1
vote
2answers
93 views

Avoid making repeated Random Integer in different iterations

Assume following code : Do[ i1 = RandomInteger[{1, 5}]; i2 = RandomInteger[{1, 5}]; While[i1 == i2, i2 = RandomInteger[{1, 5}]] , {k, 1, 4}];` This ...
14
votes
1answer
326 views

Making Monte Carlo simulation with ParallelTable

I would like to to MonteCarlo simulations of various regressions - basically, doing OLS under various conditions to test approaches. On my macpro 2x 2.8 GHz quad core Xeon, 32 Gb RAM DDR2 @ 667 Mhz, ...
0
votes
2answers
84 views

Multiplying a list and randomly re-assigning that list to a series of numbers

I'm trying to write a script that matches a particular element to a coordinate. Let's say there are 24 coordinates; and that fractionally a:b:c:d:e is 18%:18%:18%:18%:27%. Instead of matching 4 of a, ...
8
votes
1answer
184 views

Inconsistent DistributionFitTest results?

In pondering this question, I used Mariana's function to generate the following data. ...
8
votes
2answers
728 views

What is the best distribution for my histogram?

I defined a security bound for a random walk (cube with 15 lengh) and i have this code to obtain a sample of the random times at which the random walk crosses the boundary for the first time: ...
3
votes
1answer
171 views

Sample of the random times at which the random walk crosses the boundary

I defined a security boundary for a random walk: ...
2
votes
2answers
173 views

Color of first and last point in a graphic

I'm trying to make a graphic of a random walk in 1D, but i want that the first and the last point have a color (in this case the first one red and the last blue), but i dont know what i'm doing ...
6
votes
2answers
725 views

Random walk on a sphere [closed]

I'm trying to programme a random walk on a sphere with Mathematica. I found this code while I was searching, but I'm not getting results from it. I waited an entire day, but my pc didn't finish ...
1
vote
0answers
84 views

What is the fastest way to obtain the eigenvalues of a Wishart matrix?

I would like a fast method of creating a sample of random numbers which corresponds to the eigenvalues of a Wishart matrix: For M>N the eigenvalues \lambda_i are given by the jpd Where $K_N$ is ...
4
votes
0answers
80 views

Converting problem into form involving Probability

I want to solve the following problem symbolically, using Probability: What is the probability of the first random variate of a set to be present more than ...
2
votes
3answers
128 views

Performance on Multinomial Deviate is slow

Most of the time in my program is spent on this single line of code: out = RandomVariate[MultinomialDistribution[nt, tmp]]; ...
4
votes
1answer
84 views

RandomSample Bug?

I was using RandomSample with very skewed weights. I am asking for a random sample of 6 numbers 1 through 100 without replacement. In the screen shown, the weights for 1 through 6 are 100 000, with ...
6
votes
2answers
107 views

Algorithm in RandomChoice[{w1,w2,…}->{e1,e2,…},n]?

I wonder if someone happens to know the actual algorithm implemented in the particular overload of RandomChoice that handles explicitly presented discrete ...
2
votes
1answer
245 views

Does RandomInteger[{0,n}] disfavor n? [closed]

I am puzzled by the following behavior of RandomInteger. Table[{k, Histogram[RandomInteger[k, 20000]]}, {k, 10, 100, 10}] ...
1
vote
1answer
107 views

BlockRandom and NestList: how get random maps with the same noise?

I need to compare solutions in random systems with the same noise and different initial conditions. Here I run twice a random map with the same initial condition, inside a ...
9
votes
4answers
270 views

How can I generate and randomly assign color to annular sectors?

How can I generate such an image and fill every annular sector with a random colour?
6
votes
1answer
201 views

Generating a (random) 2-dimensional cellular network

I want to generate a network of random cells like the following picture: The general idea is to generate some random points (x,y) as coordinate of a vertex and then randomly choose some of these ...
2
votes
1answer
109 views

Expectation of GeometricBrownianMotionProcess

I am trying to compute $$\mathbb E\left[\max\left(\frac{S_{1/2}+S_1}{2}-K,0\right)\right]$$ where $K=100$ and $S_t$ is a geometric brownian motion (with $S_0=100$, drift $r=0.05$ and volatility ...
3
votes
1answer
173 views

How can I selectively trigger computations in Manipulate?

I have a Manipulate that uses RandomVariate and Random that I would like to have redraw and ...
1
vote
1answer
118 views

Need help scoring randomly generated SEC football rankings

So my task is to score all the possible rankings of the 14 SEC football teams and find the best one, using who won in head-to-head games as the sole criterion (so not factoring in strength of schedule ...
9
votes
2answers
287 views

Counting and extracting hit circles/triangles for randomly chosen points

Below, you see a triangle in which the incircle was inscribed. As we know, the center of this circle is the intersection of the angle bisectors. At this point, one could go further and find the ...
3
votes
1answer
104 views

Recursion when randomizing elements in a list

I want to randomize certain elements of a list; Since the code list = {a, b, c, d, e, f, g}; list[[{1, 3, 5}]] = RandomSample@list[[{1, 3, 5}]]; list works fine, ...
6
votes
2answers
178 views

Generated Numbers under a constraint?

Let's say I have five four dimensional vectors $p_i^\mu=(p_i^1,p_i^2,p_i^3,p_i^4)$ with $i=1,2,3,4,5$. Now, I want to fill the entries of these vectors ($4\cdot5=20$ in total) with some numbers, but ...
1
vote
4answers
275 views

How do I create a list of 25 random quadratic equations in the form ax^2+bx+c?

My teacher suggests using the RandomInteger command along with the Factor command, but I cannot figure out the syntax. A, b, and c need to be non zero integers between -10 and 10.
0
votes
0answers
43 views

Using an Interpolating Function as a probability density function [duplicate]

I have seen a couple of similar questions but have not been able to figure out a solution for my particular problem. I have a probability density function of two variables ...
6
votes
3answers
482 views

How to randomly erode a 3D distribution of points with Mma 7.0?

Suppose we have a 3D distribution of points, like the spherical ball example below : ...
-4
votes
1answer
358 views

How to generate this fractal-like 3D distribution of points in Mma 7.0?

I would like to produce some 3D distributions of points using Mathematica 7.0, that look like the picture below : How could I do that ? What are your suggestions ? What Mma 7 codes could do a ...
4
votes
3answers
256 views

Creating a function with integral zeroes of the 0th, 1st, and 2nd derivatives

I would like to be able to randomly generate functions, each of which satisfies $f : [-10, 10] \rightarrow [-10, 10]$ All the zeroes, critical points, and inflection points have an integral ...
2
votes
2answers
91 views

Random Choice: List Format & Minimizing Memory Use

This is a two part question, and for that I apologize.. but they're related! Here's what I'm working with: ...
0
votes
2answers
226 views

Generating a random tree of given cardinality, depth, and labeling

For demo, exploration and teaching purposes, I would like to be able (and asking you for help) to generate these special instances of trees: For given: N - number of nodes in the tree D - depth of ...
2
votes
2answers
63 views

Avoiding RandomVariate update with use of Locator

I am preparing an activity that simulates the response from a noisy spectrometer. The function I use to generate the data has the form: ...
1
vote
1answer
85 views

RandomVariate[LogNormalDistribution] works not as expected

I currently simulate data with a lognormal distributed covariate. I used the following code to check the generated random numbers (with Mathematica 9). ...
2
votes
2answers
209 views

Fast randomization of a graph, while keeping the graph connected

I'm looking for a very efficient method for randomizing graph of a given size (N nodes, L links), but keeping them connected. Assume you have the adjacency matrix A of a given connected graph. You ...
2
votes
1answer
45 views

How to randomly select and open a notebook using CDFPlayer

I have a lesson notebook for a class I am teaching. I'd like to separate the lesson content and the practice problems. Students are using the CDFPlayer program, not Mathematica. I created a button ...
92
votes
7answers
15k views

How to generate a random snowflake

'Tis the season... And it's about time I posed my first question on Mathematica Stack Exchange. So, here's an holiday quest for you Graphics (and P-Chem?) gurus. What is your best code for generating ...
15
votes
4answers
1k views

Finding the volume of a sphere using the Monte Carlo algorithm

I used the following code to find the volume of the sphere $x^2+y^2+z^2 = 1$ in the first octant: ...
9
votes
4answers
388 views

Why is Poisson Random Deviate Generation so slow?

I am generating Poisson deviates for some numerical work. Mathematica 9.0.1 is very slow in generating these random numbers, as can be seen below. ...
2
votes
2answers
179 views

How to restore default seed generation in SeedRandom[] when specifying method?

I want to generate low-discrepancy sequences and for that purpose I use SeedRandom[], like: ...
-1
votes
1answer
59 views

map rational number [duplicate]

I am trying to map this function ((-1)^(1/Denominator[#]))^Numerator[#]==(-1)^#& to a fairly big list of random rational numbers I am trying to get this to ...