Questions tagged [sparse-arrays]

Questions on the construction and manipulation of sparse arrays in Mathematica, with functions like SparseArray[] and Band[].

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2
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3answers
158 views

How I can generate a matrix from a set of terms?

I want to build a matrix, from the following set $S = \{a b , a c\}$ S = {a b , a c} where the terms of S represent the raw of the matrix ...
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0answers
165 views

Find Eigenvalues close to a Target for a Generalised Eigenvalue problem of the type Ax=λBx with A and B very sparse

So I have been using Mathematica as a tool to discretise large linear systems of PDEs and cast them as algebraic eigenvalue problems involving very large sparse matrices. These are usually complex and ...
6
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1answer
217 views

Why does SparseArray allow some patterns but not others?

When building a SparseArray, patterns of the form {i_, i_} and {i_, j_} are fine, but ...
6
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2answers
121 views

Using sparse matrices when value depends on position

I am working with solving a linear system that becomes a tridiagonal matrix. In order to speed up the process for large matrices, I want to use sparse matrices. My problem is that the values are not ...
3
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3answers
1k views

How to create a lists of matrices?

I would like to creat a list of matrices from the following rules: 1- All matrices of the list have diagonal equal to zero. 2- The first matrix have 2x2 dimension, ...
2
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2answers
181 views

Creating a list of arrays according to given rules

I want to create a list of matrices from the following rules: All matrices of the list have diagonal equal to zero. The first element of the list is a 2x2 matrix, having elements are given by ...
0
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1answer
122 views

Parse large ASCII matrix

I am parsing a large ASCII sparse matrix, output of PETSc, but my current implementation is impossibly slow. I don't know how I could speed that up. The ASCII file of a sparse PETSc ...
3
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1answer
294 views

Problems with RandomChoice

Consider an Matrix of dimension n1xn1. I would like to get a list with n2 distinct matrix (of dimension ...
6
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2answers
234 views

Why the sparse array is ill-conditioned?

Bug introduced in 8.0 or earlier and persisting through 11.1.0 or later Given that I have a knot vector $\mathbf U$ and a set of parameter values $\mathbf T$: ...
2
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1answer
178 views

Build sparse matrix in mathematica knowing position i,j and value to store, from file

I have a file formatted in this way: Row Column Value i j Vij i= INT Number row where in sparse matrix I want the ...
3
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2answers
180 views

Merging SparseArrays (or normal arrays)

I have a list of SparseArrays, and I want to combine them into one array that concatenates their rules. I don't want to connect them together like ...
6
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1answer
153 views

Multiplying SparseArray by negative number Crashes Kernel

Bug introduced in 9.0 and persisting through 11.0 Can anyone reproduce the following bug, or figure out a work-around. The following crashes the kernel on both Mathematica 10 and 11, on my macs, ...
6
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1answer
136 views

Nonsparse SparseArray crashes the Kernel

Bug introduced in 10.0 and fixed in 11.1 On Windows 10, 64 bit, version 11.0.1, my kernel just started crashing for no reason as for as I can see. Does/should the following crash your kernel? ...
3
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0answers
54 views

Map entries of StructuredArray

I have the following defintion arr = SymmetrizedArray[{1, 2} -> 1, {4, 4}, Antisymmetric[{1, 2}]] which gives a ...
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0answers
69 views

How to modify the default value of a `SparseArray` without intermediate non sparse matrices [duplicate]

How to modify the default value of a SparseArray? All of my ideas doesn't work, because of the ReadProtected attribute. Is there ...
7
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2answers
264 views

directly change the background value of a SparseArray?

given a SparseArray s = SparseArray[{1, 10} -> 1, {1, 10}, a] I can extract the background value (see What are SparseArray ...
7
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1answer
219 views

Bug? Strange behaviour of FullSimplify when checking an equality of SparseArray's

Edit (15 Dec '16): bug noticed in v11.0 and reported as CASE:3796403. Edit (03 May '17): bug fixed in v11.1 (verified in v11.1.1). I stumbled upon the following strange behaviour. Disclaimer: I ...
7
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4answers
411 views

How to find position where a sequence drops off to zero

Suppose I have a sequence seq = {0,0,0,1,2,3,1,0,0,0,4,5,8,0} and I want to find the first position after which the sequence drops to zero (which in this case, is ...
0
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1answer
226 views

How to build a histogram from the mean of 100 matrices

I have a matrix that looks like this: ...
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0answers
36 views

Sparse (Weighted) Adjacency Matrix & SparseArray: encoding multiple weights at a given edge [duplicate]

Context Below is just an arbitrary example. It is not perfect, but hopefully it serves the point of what I would like to accomplish. Say you have a sparse adjacency matrix, $\bf{A}$, where a value of $...
2
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1answer
90 views

How to fill in matrices by enforcing a condition on each entry quickly?

In the process of solving a 3D time-dependent PDE, I need to fill several matrices which their sizes are quite high. These matrices are constructed based on the radii of the mesh nodes in the 3 ...
5
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3answers
117 views

Sparse array approach to generate a Colm Mulcahy matrix

I wrote: ...
2
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1answer
1k views

How to find position of non-zero elements in SparseArray without converting to a dense object

Overview So I have a SparseArray, sparse, constructed from a list of rules, with the dimension options. Given a row, I want to know where the values are non-zero. ...
1
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1answer
215 views

How to create a matrix with some conditions?

I want to create an $n \times n$ matrix (eg. $n=5$) using the following steps: 1) The entries aii (i = 1, ..., n) that form the main diagonal of a square matrix are 0 (aii=0); In C++, the element of ...
6
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1answer
276 views

Pardiso Linear Solve Method

It seems that "LinearSolveMethod" -> {"Pardiso"} is not available on the Raspberry Pi 3 version (10.3, 32-bit Linux, ARM) of Mathematica. Is there a package that ...
1
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0answers
46 views

Looking for a package for data on (sparse) uniform grids

I have large amounts of sparse 2d and 3d "volumetric" data, i.e. fixed data associated with positions in a uniform (integer coordinate) grid. I think of it as partial function $$f: \mathbb Z^n \to D.$...
4
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1answer
188 views

How does AdjacencyLists work on SparseArray

I have been working with large SparseArray and have noticed the properties are very very useful and fast. I wanted to manipulate my large sparse array in ways similar to the properties. Looking at the ...
6
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2answers
3k views

How to export an output matrix obtained in mathematica to a matrix in python with the correct format?

I have a large sparse matrix as the output and I want to save the output and open it as a matrix in python. The output is a 6000 x 6000 matrix and I don't know how to make changes to the file such ...
4
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1answer
664 views

Why am I losing precision in computation of eigenvectors of sparse matrices?

I compute the eigenvectors and eigenvalues of the same matrix in its dense and sparse version. The eigenvalues are the same to great precision, but the eigenvectors are not: when I compute the ...
1
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1answer
161 views

Converting a list of lists of indices into a sparse matrix of ones and zeros

I have data formatted like {{a,b},{c,d},{e,f}} where each entry is an integer. I need to turn this in to a sparse array with entries ...
4
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0answers
92 views

Why isn't SparseArray working in this case?

This works: SparseArray[{{1, 1} -> 1, {2, 2} -> 2}]\ (* {{1, 0}, {0, 2}} *) This works: ...
6
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1answer
216 views

Efficiently compute this Table of NullSpace

I have two $(2n,2n)$ matrices, $A_1$ and $A_2$, and I would like to compute $$\ker(A_1^p A_2^q -I)$$ for $p,q\leq 2n$. Both matrices are orthogonal and have exactly four non-zeros values on each ...
11
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2answers
504 views

Why is IdentityMatrix not defined as a SparseArray by default?

Simple (possibly silly) question: why are IdentityMatrix, DiagonalMatrix, ConstantArray ...
2
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2answers
212 views

What would be the Mathematica equivalent of sparse in MATLAB?

The sparse function in MATLAB does the following: S = sparse(i,j,v) generates a sparse matrix ...
12
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1answer
197 views

Something wrong when I apply Derivative on a SparseArray

Bug introduced in v5.0 or earlier, and persisting through v11.0.1 or later There, I create a SparseArray using command ...
10
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2answers
160 views

Using Cases to pick out entries of a SparseArray

I'm trying to use a SparseArray for some large homological algebra calculations. I'd like to find indices of a SparseArray ...
10
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1answer
162 views

Possible Bug in LinearSolveFunction with Sparse Vectors

Bug introduced in 5.0 and fixed in 11.0 LinearSolveFunction is new in 5.0 Consider the following set of equations and corresponding variables: ...
0
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0answers
417 views

How to compile code that involve sparse array?

I have the following code ...
7
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3answers
935 views

Nonzero element positions of a matrix

Let m={{1, 2, 0}, {4, 0, 9}}; I want to find the position of every nonzero element of the above matrix. The code ...
4
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1answer
240 views

How to create overlapped block matrices and simplify the result

This is sort of a duplicate of Creating overlapped block matrices, but the question wasn't fully answered since the OP never returned to clarify. I am using Kuba's answer for FEM, but I have been ...
2
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3answers
2k views

How to convert a matrix into a sparse matrix [duplicate]

If I have a matrix: row 1)1 0 0 4 row 2)0 0 0 0 row 3)5 1 0 0 row 4)0 5 0 0 row 5)0 0 0 9 How would I put it in a sparse matrix format: ...
17
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2answers
248 views
4
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1answer
480 views

efficient elementwise multiplication of SparseArray vector and matrix

I have a large $d\times d$ SparseArray $P$, and I want to multiply a vector (also a SparseArray) $v$ of length $d$ elementwise ...
11
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4answers
936 views

How to convert a sparse matrix to a list of sparse arrays?

I have a matrix stored as a SparseArray. How can I convert it to a List of its rows, where each row is stored as a ...
5
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4answers
610 views

Constructing a large tridiagonal matrix with alternating signs

What is the best way to construct a large tridiagonal matrix, in the following form (notably with alternating signs)? $\mathbf M = \begin{pmatrix} 0 & a & 0 & 0 & 0 & \cdots \...
4
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0answers
616 views

Finding eigenvalues in Mathematica: why so slow?

I am trying to find the eigensystem of a large sparse real symmetric matrix, and I only need the lowest 40 or so eigenstates. The relevant code is as follows: ...
0
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1answer
363 views

LinearSolve on non-square matrices?

I just came across a strange behaviour for LinearSolve (on Mathematica 8.0.0.0). Consider the following definitions: ...
5
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4answers
235 views

Add to matrix missing elements (for list of time series)

This question is an extension of the 43122. I’ve looked through many interesting post (like this) but (as always) missed the direct matching. So the setting is simple: ...
1
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1answer
67 views

Assemble rule replacement from pairs of positions

I want to create a rule replacement list, which I then use to create a SparseArray. The input is a list of positions of the from ...
4
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3answers
189 views

Problem with Conditionals: Why does mathematica add an extra empty list to my output

I have a set of positions where I want to slice a list of numbers. If I Total the values in that list, and they are greater than or equal to 1, I want to remember ...