Questions tagged [random]
Questions about random number generation and the properties of numbers so generated.
898
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How to select random number of elements from a list?
Assume that I have a list
a = {1,2,3,4,5,6};
and I want to have a function that outputs a subset of the list such that with probability p=0.2 each element will ...
- 135
2
votes
1
answer
145
views
Random points from an image using a BernoulliDistribution
I am a Mathematica newbie. I need to sample random points from an image which I have stored in a variable img as:
...
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1
answer
316
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Why does Monte Carlo integration underestimate my integral as integration range increases?
I'm having a huge problem with Monte Carlo integration. This simple example adequately shows the problem.
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1
answer
50
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Matrix Randomization
Is there a way to take a 20x20 array and replace 2 random parts of this array with a 2x2 matrix?
I've tried
rvalues = ConstantArray[r, {20, 20}];
to make the ...
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0
votes
1
answer
161
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Negative values with RandomVariate
I am using the following code to generate some random number from a custom distribution:
...
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1
answer
51
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Am I using RandomVaraite and ProbabilityDistribution correctly?
The following code does not produce an output on my Mma (version 11.3 for Windows)
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7
votes
2
answers
459
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How can I get new random values with each blank in ReplaceAll?
Is there any way to get different values for different blanks with ReplaceAll[]? For example, I would like to do something like:
...
- 1,447
22
votes
3
answers
2k
views
Efficient way to simulate thousands of Markov chains
I am currently trying to simulate relaxation of a protein population while maintaining the stochastic properties of the system. For this, I used a Markov chain to describe the temporal evolution of ...
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6
votes
3
answers
250
views
How can I delete a random part of an expression?
I have the expression:
Times[0.19157500241430547,Power[Plus[0.7235014213631388,k,Times[-1,Power[m,c]]],Times[g,z]]]
Also represented as:
...
- 1,447
5
votes
3
answers
230
views
Improving the run time of random walk simulation
One of our professors told us that during his thesis he used Mathematica in simulating it since it is about networks, I don't know how he did it but all I know is he said it took about two weeks to ...
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3
answers
829
views
Construct Distribution Histogram From Random Variable
Given a Beta Random Variable $X$ with parameters $\alpha, \beta$ and a positive constant $n$, suppose I am interested in the distribution of:
$$Y:=\lfloor nX\rfloor$$
Suppose I want a histogram ...
- 1,111
2
votes
1
answer
84
views
Apply RandomReal to list in list in Mathematica
I have a big list: {{1,1,1},{1,1},{1,1,1,1,1,1,1}....{1,1,1,1}}
How can I apply RandomReal to every single element in the list?
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5
answers
992
views
Evenly spaced points on boundary of polygon
I have a polygon and I would like to generate $n$ evenly spaced points along the boundary.
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5
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1
answer
512
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Acceptance Rejection Method
I need to generate a random number (real) and then test if this number works on my pdf. if it works i append it to a list. if it doesn't, i reject it.
Until now i have done this:
...
- 203
3
votes
0
answers
202
views
Generating random coordinates (3D) with constraint
I have been trying to generate random $(x,y,z)$ coordinates (i.e. for 15 ellipsoids) so that they obey following constraints:
ellipsoid's length is constant,
ellipsoids do not intersect (fulfilled ...
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4
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2
answers
169
views
Optimize RandomVariate for a $1/x^4$ distribution
I'm working with the following code, where I define a probability distribution proportional to $1/x^4$.
...
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0
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1
answer
100
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Generate random point on the external surface of this complex geometry
This is a followup to this question of mine.
How do I generate a random point on the most external surface of this complex geometry?
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0
answers
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How to ask FindClusters to return the loss function value in the output?
I have some data points pts as below:-
pts = BlockRandom[SeedRandom[123]; RandomReal[1, {100, 2}]];
Now I want to separate ...
- 3,469
11
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2
answers
5k
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Generate "nice" random matrix
I don't frequent this community, so please give criticism if this is a poor question.
I am trying to make a tool which generates a small (say, $4\times 4$) matrix with integer entries, which has a "...
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1
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0
answers
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Bizarre error messages when monitoring random integers
I am doing
tbl = {};
Monitor[
Do[AppendTo[tbl, RandomInteger[{1, 100000}, 2]], 100000],
Length[tbl]
]
(well in fact I am doing something less boring but what I ...
- 2,066
4
votes
1
answer
199
views
How to generate a random real under a specified density function?
I want to generate a random real in the interval [0,1] according to the density function f(x) = 2x.
- 1,661
5
votes
1
answer
497
views
Random walk in one dimension — meeting of two particles
I'm new to Mathematica and still teaching all by myself, hope you bear with me.
I have the code:
...
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1
vote
0
answers
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RandomVariate with a custom distribution [duplicate]
I have a customized distribution and I have to draw some random number from it.
How do I use RandomVariate to draw random number from a custum distribution? My naive attempt ...
- 6,687
6
votes
3
answers
363
views
Generate a random pattern with at-most n repeated consecutive elements
I want to generate a random pattern which has at-most n (>= 0) repeated consecutive elements from a sample space. The following example explains what I mean:
...
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1
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195
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Getting PDF from imported Histogram
So I'd like to create a probability density function from an existing histogram from a program that I use. My input data is of the form
...
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5
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1
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280
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Sampling "Random" Cyclic / Acyclic Graphs
This is an extension of RandomGraph with specific constraints
Where @Histograms wanted to make $n$ random graphs with a specific constraint (in @Histogram's case, having 2 vertices each with exactly ...
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3
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141
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Uniformly distributed numbers fulfilling conditions
I would like to generate 10 random lists of four elements (t, l, p, ...
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0
answers
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Can this code be changed to run faster?
I've worked for several days trying to get this code to run faster. The imported data is 15MB.
...
- 1,637
2
votes
1
answer
146
views
Evaluation Time of RandomVariate Function
This question is about the runtime of the function RandomVariate.
Take a simple normalized Gaussian distribution G on the real line, I tried to generate N random ...
- 131
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votes
3
answers
2k
views
Creating a random matrix of no duplicates in both row and column from a given set list of elements
Say I have a list of letters {A,B,C,D,E,F,G,H}, I want to create an $4\times 8$ array where each row must not contain duplicates and each column must also not contain duplicates.
Naively writing:
<...
- 577
3
votes
2
answers
322
views
Is a probabilistic primality test implemented in Mathematica?
Imagine that I need to verify that a specific integer, like $n = 10^{1347}+3049$ is prime.
ProvablePrimeQ takes a lot of time, and, even if it will eventually work ...
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7
votes
2
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483
views
Creating a less random list
I'm trying to create an list like {1,3,2,5,8,7,9}, or {2,1,5,6,4,7,9}, that the elements in each list is sorted in a rough order,...
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1
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341
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Random particle motion
I have a foundational function that allows me to simulate particles moving in a box according to some movement function. The code is here:
...
- 3,634
1
vote
0
answers
73
views
Looking for a way to run through every time step of a cellular automaton function with random seeds
I have been creating 2D cellular automaton functions in Mathematica and I would like the output to be a graphical representation of the array at each time step. I know I can do this with ListAnimate: ...
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1
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5
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1
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79
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Random normalised variable generation
I want to generate 8 random variables (in reality to form 4 complex numbers) such that the sum of the 8 variables squared is equal to unity. The aim of generating such numbers is to perform a quantum ...
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2
votes
4
answers
222
views
How do I use the values generated in a for-loop in my first iteration to my next iteration?
This one is somewhat hard to explain, but I'll try my best to.
I'm trying to generate a list of numbers (containing only pi/10, 0, -pi/10). Numbers are randomly selected from these 3, where the ...
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votes
1
answer
144
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Defining a random potential on the unit square
I'm trying to define a random potential on the 2D unit square. For some fixed j, I want to decompose the unit square into $2^{2j}$ smaller squares with sides length $2^{-j}$. On each of the smaller ...
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1
answer
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3
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0
answers
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RandomPoint not evaluating on RegionQ and ConstantRegionQ regions
When attempting to recreate and generalise the MatLab code for Random Vectors with Fixed Sum by first principles I came across a few issue with RandomPoint.
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3
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Random Point on Edge of Cylinder
How can I get a random point on just the curved edge of a cylinder?
c = Cylinder[{{0, 0, 0}, {0, 0, 2}}, 2];
RandomPoint[RegionBoundary[c], 50]
almost works, but ...
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3
votes
0
answers
60
views
RandomChoice inside RandomChoice
I have spent a half hour searching Mathematica.SE for information on this topic, with no luck. The code is:
...
- 1,637
1
vote
2
answers
344
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Using "RandomFunction" to simulate a Itoprocess with Random initial condition
I have an itoprocess such as:
...
- 13
0
votes
1
answer
166
views
RandomReal left randomly unevaluated
Can anyone explain this?
In Mathematica 11.1, I have a piece of code that uses RandomReal. Every so often I will throw up a RandomReal::array error. This happens ...
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votes
0
answers
26
views
Store the output values from a random sample [duplicate]
I am new to programming. I am defining x and y as random samples(as mentioned). Then I define a function h (of x and y). Now I want to get output values of h multiple times at once. I want to store ...
- 35
0
votes
1
answer
303
views
Sphere Point Picking in Cartesian coordinates [closed]
I have a vector $\vec{A}(x, y, z)$.
Now I want to rotate the vector randomly (x by ϕ, y by ...
- 556
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votes
3
answers
486
views
RandomPoint doesn't seem to work
I define a very simple sphere in 3D as follows:
ℛ = ImplicitRegion[(x - 2)^2 + (y - 3)^2 + (z - 8)^2 == 1, {x, y, z}];
Now when I try to sample some 500 points ...
- 1,534
5
votes
2
answers
239
views
Random sample of big big numbers
Consider the following piece of code:
m = 2;
n = 6;
samplesize = 1000;
totalsize = 2^(n^m);
numbersample = 2 RandomSample[Range[totalsize/2], samplesize];
With ...
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