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Questions tagged [array]

Questions about Mathematica arrays, or implementing array data-type functionality, i.e, collections of regular dimensions containing elements that can be accessed by standard (computable) indices.

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2answers
14 views

Create symmetric array of function values

I have function B[i,j] where i,j are integers. Then I create array: b = Array[B, {3,3}] now I set values of ...
7
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4answers
204 views

Generate an array with custom index

Apologies if this is a duplicate. I am trying (but failing) to generate the following n x n matrix in Mathematica: where G[tj, t0] is a function along the main diagonal and G[tj, tj] is a function ...
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0answers
42 views

How to evaluate an expression [on hold]

I have a 3-dimensional array of numbers say A. I want to evaluate the following expression. $\displaystyle\sum_{\sigma,\tau \in S_6}(\Pi_{i=1}^6A(i,\sigma(i),\tau(i)))$. $S_6$ is the symmetric group ...
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22 views

Filling Regions (Blocks) of a Binary Matrix with Different Probabilities

This is an extension of the following question: How to generate binary array whose elements with values 1 are randomly drawn, where the most elegant answer was posted in the comments: ...
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2answers
45 views

How can I convert a matrix of 3d experimental data into a 3d list which can be interpolated in a f(x,y) function

I have a 3d experimental *.txt data with the form: y1 y2 y3 x1 f(x1,y1) f(x1,y2) f(x1,y3) x2 f(x2,y1) f(x2,y2) f(x2,y3) x3 f(x3,y1) f(x3,y2) f(x3,y3) I need to ...
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2answers
67 views

How to create an array of function values omitting certain values

I'm using Array to create function lists, f[1],f[2],f[3],...,f[A] where the values from $1$ through $A$ have unit increment. ...
2
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1answer
45 views

How to remove curly brackets in a two dimensional array near the edges?

Suppose I have a matrix {{1,2,3},{4,5,6}}. I want to remove the curly brackets near the edges, i.e., I want an output as '{1,2,3},{4,5,6}'. Somebody please help me to solve it.
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1answer
31 views

Array[] for lists with vector-like functions

I would like to use Array[] or a similar function that gives out a list of vector-like functions evaluated at different numbers. For a scalar function f this is perfectly doable with Array[]: ...
2
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2answers
95 views

Map vs. Table for index-specific operations on 2D arrays–Part II

This is an extension of my recent question, Map vs. Table for index-specific operations on 2D arrays For that question I gave a minimal working example, since I was more interested in learning ...
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1answer
27 views

Creating a tensor of rank $k$ from elements of a list

Given a list containing $4^k$ elements, how do I create a "square" $\underbrace{4\times...\times4}_{k\text{-times}}$ tensor of rank $k$? Intuitively, I would opt for the ...
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2answers
72 views

Function of an array with argument

Suppose c[i,t] is an array such as c[1,2]={1,2,3} I want to define a function TOT[c[i,t]] which, for instance, computes Total[Array]. This does not work: TOT[c[i_,t_]]:=Total[c[i,t]] Any help?
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1answer
29 views

Simplest way to export (and import) definitions?

Consider I have this code : f[1]=2 f[1.5]=6 f[3]=4 What is the simplest way to save the array f defined on those three numbers in a file ? (in my case, I will ...
2
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1answer
84 views

Bivariate Array Arrangements

I want to Generate a bivariate data set (X,Y) of m*m Arrange each row with respect to X Note the order of Y associated with X From the first row, pick the first element order of X, along with Y and ...
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2answers
44 views

Sum up different arrays into a new array

I have a question regarding sums in arrays. So I have the following array: ...
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0answers
31 views

How to run image manipulation function to an array of images?

I have multiple images imported into an array. My issue begins with using this array for an image manipulation function such as Inpaint. Inpaint only accepts a single image at a time. Here's how I ...
4
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1answer
91 views

How to draw individual mesh lines in ArrayPlot

Consider the following ArrayPlot. ...
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2answers
129 views

Flatten a four dimensional array into a matrix

What is the simplest way to transform an array of the form ...
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1answer
39 views

Generating columns in table and header for exported data file automatically

I have a code that goes like this: ...
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1answer
59 views

How do I create a Jacobian matrix for a large system of equations?

I would like to create a Jacobian matrix using the simplified functions below: f1[a_,b_,c_]:= a^2 + b^2 f2[a_,b_,c_]:= c/2 f3[a_,b_,c_]:= b^3 I say simplified ...
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2answers
354 views

How to read .npy file in Mathematica?

I have a .npy file which is created by numpy of Python as below:- ...
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1answer
63 views

Extracting unique values from array

I performed MorphologicalComponents on an image, and from there used SelectComponents to filter out my desired components. Is there a way to extract out the unique values from the entire array? i.e. ...
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2answers
96 views

How can I import a .txt file containing a matrix of numbers and work with its columns? [closed]

I want to import a text file which has two columns. Then I want to assign one column to an array alpha[i]. Using the following command assigns the whole file to t[i]. ...
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2answers
83 views

Using good method to produce a regular matrix

The matrixform is as follow, and how can I use good method to produce it? H = {{1, 1, 0}, {2, 2, 0}, {0, 1, 1}, {0, 2, 2}, {1, 0, 1}, {2, 0, 2}}
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1answer
37 views

find in list almost equal elements, make new list correspond to position or some list

I have a list of elements called q and wish to compute Total Multiplicity of each element, and put these values in the list tm. ...
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4answers
525 views

Sort with assumptions

I have a list which looks like this list = {0, Subscript[x,7], -Subscript[x,3]-Subscript[x,9], -Subscript[x,9]}; and all the $x_i$'s are positive semidefinite (i....
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1answer
296 views

Part::pkspec1: The expression j cannot be used as a part specification

I want to do some stuff with symbolic arrays like this a[[j]] + a[[j + 1]] == a[[j - 1]] + a[[j - 2]] But upon declaring such an expression I get ...
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1answer
81 views

Drawing an approximate visualization of an inequality using ArrayPlot

I need to write a function that returns graphic visualization of the two-dimensional figure described with equation: $\qquad P = \{(x, y) \in R^2: 4+2x < x^2+y^2<9\}$ I have to use the n x n ...
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1answer
102 views

DefineDLLFunction returning array

I have an external "C" DLL function which returns a pointer to an byte array as well as the number of array elements (bytes) ...
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3answers
268 views

Converting a list of colors into an image

I want to manipulate colors, and merge the resulting vector and rasterize it into an image, controlling the resolution of the pixel. E.g. I tried to: But what I would like to have is an image of 3 ...
2
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1answer
84 views

Fast and Listable Piecewise function

I am writing a simulation where I have an array with ten columns and on the order of millions of rows, for which I need to iterate on the order of ten thousand times, making computation time a major ...
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0answers
107 views

What is the difference between an array and a list

Is there a difference in functionality between a list of lists and an array? In Python sometimes data structures are mutable or immutable. I don't see the difference in Mathematica.
2
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1answer
103 views

Mathematica incorrectly imports a table

I am trying to calculate the eigenvalues of a large matrix (10^4x10^4), which is formed by summing a matrix containing advective terms and a matrix containing diffusive terms. I am using the following ...
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1answer
44 views

Make a plot from data [closed]

I have two variables $x$ and $y$ satisfying, say, $y^2 + x < 1$, such that $0 \le x < 1$ and $0\le y<1$. I want to plot all the points satisfying the inequality $y^2 + x < 1$ and also show ...
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1answer
37 views

imposing conditions on an array within a function

Let's say I have the following function ...
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5answers
455 views

How to join many columns of data in array?

I have large number of columns of data. How to put in single matrix? For example, with test data of 1 x 3 matrixs ...
5
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2answers
147 views

Fast element-wise division of matrix, generated from vector with `Outer`, and another matrix

m = {a, b, c}; n = {{e, r, t}, {y, u, i}, {g, h, j}}; k = Outer[Divide, m, m]; k/n gives ...
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1answer
78 views

Derivative of sum of elements of array [closed]

I try to get derivative of sum of an array with respect to an element of the array. $$s = \sum_{i = 1}^{3}A_{i, 1}$$ Evaluate $\frac{\partial s}{\partial A_{1,1}}$ Below is the code. ...
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2answers
55 views

Counting the number of Configurations in an Array with Constraints

Consider an array $$\{a_i\}, i=1, ..., N$$ with periodic boundary condition, i.e. $i\equiv i+N$. $a_i\in \{0, 1\}$. I would like to count the number of configurations of the array $\{a_i\}$ satisfying ...
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1answer
82 views

change color of ArrayPlot

I have de following array: size=5; Initial = RandomInteger[{0, 1}, {size, size}]*2 - 1; to visualize it I use the following code: ...
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0answers
60 views

How can I modify an element of an array? [closed]

I have a simple array like this one: myArray = {1, 2, 17} At some point I want that 2 to be a 4. How can I change it?
23
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1answer
295 views

Which second arguments is VectorQ/MatrixQ/ArrayQ optimized for?

VectorQ and similar functions (MatrixQ, ArrayQ) treat certain second arguments specially. ...
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0answers
24 views

Plotting an element of large array is slow

I get a slow down when using ContourPlot on elements of a large array of messy expressions. That is, if fooArray has 100 elements and I plot the first 3, that's much slower than if fooArray has 3 ...
1
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1answer
65 views

Evaluating the 1st argument of Set

I want to assign a certain value to an element of a tensor. This element is identified by an array obtained from some evaluations, so we fix it. Here i present an oversimplified core part of my code: ...
1
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1answer
429 views

Tag Times in Null is Protected [closed]

I've some problems with the error mentioned in the title. Unfortunately, my code is full of subscripts so I'll show it in a photo. In this code the central aspect is to assign a scalar value to an ...
0
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1answer
76 views

Position for array

how does Positionwork for array? In particular if i have something like this: ...
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2answers
41 views

Change value of boundary of a multidimensional array

How can we change the value of boundary of a multidimensional Array with arbitrary rank. I tried to extract the indicies with: ...
9
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3answers
528 views

Removing lists with zero at any position

I want to delete the complete list within a list containing 0 at any position. I tried using: ...
10
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2answers
476 views

Mathematica equivalent of NumPy broadcast addition for large arrays [duplicate]

What is the Mathematica equivalent of the following Python code with the vectors' broadcast addition? ...
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2answers
254 views

Populating an array in do loop, allocating memory or not

I am doing a calculation where I have a do loop can be as long as 1 million. In each loop, I want to store a value into an array to plot afterward. In MATLAB normally I was preallocating the memory ...
2
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1answer
261 views

Flatten a list at some level

I wonder if is possible flatten a list at the last level without flattening at the first level, I think that isn't a good explanation so here is my code ...