# Questions tagged [matrix]

In mathematics, a matrix (plural matrices) is a rectangular array of numbers, symbols, or expressions, arranged in rows and columns. The individual items in a matrix are called its elements or entries.

30,867 questions
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### Python Matrix multiplication for making grid

Is there any simple way/command in Python to make two (or three) matrix multiplications to get Product Kernel, e.g. expanding for grid ? I mean points should be evaluated for each combination of grid. ...
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### Function that creates matrix 5x5 + function that creates HTML view of the matrix

I got the following task: "Implement a function numberMatrix() (using JS) which creates HTML view of matrix 5x5 like mentioned below: 1 3 3 3 3 2 1 3 3 3 2 2 1 3 3 2 2 2 1 3 2 2 2 2 1 ! Note: It ...
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### Insert array elements into matrix

How can the elements from (take only range 3 to 8) a = np.array([1,2,3,4,5,6,7,8,9]) go to A = np.array([[0,0,0], [0,0,0]]) Ideal output would be: A = ([[3,4,5], [6,7,8]])
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### including rowname when using sapply

I am trying to apply a function to a dataframe using sapply. The function is the Erlang C calculation which I found from one of the sites that I came across while researching. What I am having ...
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### How to apply classification machine learning methods on a dataset in matrice format? [on hold]

I have a dataset related to 27 different subjects. For each subject, I have a 2D matrix of 100*32. I would like to do a binary classification, i.e. each subject (27 subjects) has a label of 0 or 1. ...
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### Efficiently reshuffling a long matrix into one consisting of column bound subblocks (of the original) in R

"I have a very long matrix, measuring 30^5 x 3 entries. I basically consists of subblocks of 10.000 30 x 3 matrices, stacked on top of one another. I want to afficiently "cbind" them, next to one ...
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### how to fix Matrix dimensions must agree

I am trying to plot Z0 in term of t I get this error Matrix dimensions must agree. I know that ‘T’ is a scalar, and ‘X’ and ‘Y’ are (51x26) matrices, and ‘t’ is a (1x501) vector.It is not possible to ...
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### Matrix vs function for matrix operations

Since I couldn't find anything about this subject, I decided to ask this question here. I am completely beginner and this question might be ridiculous. Suppose we have A(NxN) matrix and a column ...
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### Apply a function to every column of a matrix

What is the most efficient and concise way to apply a function to each column (or row) of a matrix? Suppose I have a matrix, and to simplify, a minimal working matrix: julia> mtx 4×2 Array{...
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### Calculating adjusted p-values from matrix while retaining matrix dimensions in R

I calculated between- and within-individual correlations using the statsBy function from the psych package as follows: statsBy(df[,c(1,10,12,13,14,17,20,24:25)], "group", na.rm = TRUE) I then ...
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### How to make dot.product of 2D and 3D matrices (taking it for each dimension separately)

I need to calculate dot product of two matrices. Probably tensordot would do the job, however I am struggling to figure out exact solution. The simple option res = np.dot(x, fullkernel[:, :-1]....
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### Simplest way of getting the neighbors of a cell in a grid (or matrix)

I'm often facing this situation where I need to find the existing neighbors and I am still not satisfied with the solution I use. In the event of a squared grid (or a dim2 matrix), like: [[ 1, 2, 3, ...
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### Creating a Square Matrix

Hello can someone please help me, I'm trying to do a square matrix in java with this format: 1 | 6 | 7 | 12 2 | 5 | 8 | 11 3 | 4 | 9 | 10 What I want is that the code generates a table with the ...
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### Uniqe ID in list of indexed 2D/3D Image masks (or 2D/3D matrix) in R

I want to make a "global" ID of 2D/3D nuclear masks across a list of images. When i segment my cells they are numbered from 1:numberOfCellsInEachImage. but I would like to have an uniqe Id for each ...
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### Efficient way of computing quadratic forms for outer product matrices

I'm currently computing a quadratic form by taking a known vector and using the element wise multiplication of two outer products as the input matrix. To be specific, my code looks something like this ...
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### Why android.Matrix.setRotateM returns a matrix whose rotation direction is the opposite of the expected rotation matrix?

For example, if I give the following parameters: float[] rotateMatrix = identityMatrix.clone(); Matrix.setRotateM(rotateMatrix, 0, 90, 0, 0, 1); I expect a matrix which rotates 90 degrees counter ...
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### Cluster a Binary Matrix

I'm looking to create clusters around all 1s and 0s. Similar to Mindsweeper, I want to basically "draw a circle" around all 1s, and create a border where 0s exist. I have tried using hclust() and ...
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### Looking for a good Computer Vision framework for Android Studio

I am looking a good computer vision API or android studio framework class, like OpenCV (I need other one, develop by google). What I need is read mobile camera data, in matrix representation. ...
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### Power BI : Matrix Get the difference of two columns

I am trying to figure out how to get the difference of two columns within a row in Matrix everything that was available in the community has been hardcoding the values of the column label. I would ...
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### matrix index matching for large raster data

I have a large raster data (X) with a dimension of 32251*51333. The values of X are repetitions of another array (Y), which has a size of 3*10^6. Now I want to change the values of X by matching it ...
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### Fastest way to save coordinate matrix as image matrix in R

I have lots of points (coordinates) and I wish to store it as image matrix dx x dy such as missing values mark as 0, otherwise put 1. sample: > s [,1] [,2] [1,] 452937.5 359878 [2,] ...
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### Make a matrix with NA values numeric

I haven't got the newest question but already read and tried everything I could find and none worked. My goal is to make a heatmap from a data with a lot of NA values. I have a 177x11 xls table, my ...
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### Zoom to point with a matrice C#

I would like to make a simple zoom to point, using matrices. I've tried several ways, like scaling the matrice with a zoomfactor, but it only zooms to the upper left corner (0,0). How do i achieve to ...
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### Svg scaling rotated elements on mouse drag

I'm playing around with svgs and matrixes for a project I'd like to work on and I'm trying to implement a free transform with vanilla javascript. As of now I am able to do all transformations with ...
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### Convert a data frame to matrix using indexing [duplicate]

I have a data frame like below: df<- read.table(text = "A B C a1 abcd 1 b2 abcd -1 c2 efgh 1 v4 uh 1 g5 vghvb 0 ",header=T) and I want to convert to a matrix like this: ...
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I have a large gzipped file (5000 columns × 1M lines) consisting of 0's and 1's: 0 1 1 0 0 0 1 1 1....(×5000) 0 0 0 1 0 1 1 0 0 ....(×1M) I want to transpose it, but using numpy or other methods ...
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### Reshape matrix by rows

I have a matrix with size 18000 x 54. I would like to reshape it as a matrix with size 54000 x 18, in which each row of my initial matrix becomes a matrix which has 3 rows. Let's take an example. I ...
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### How to speed up writing to a matrix in a reference class in R

Here is a piece of R code that writes to each element of a matrix in a reference class. It runs incredibly slowly, and I’m wondering if I’ve missed a simple trick that will speed this up. nx = 2000 ...
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### How to solve the SVD problem with the constraint that the subspaces spanned the first K left and right vectors are the same?

I'm trying to solve the problem of finding the K leading 'singular vectors' of a matrix. Different from the standard SVD problem, I need the subspace spanned by the left and right 'singular vectors' ...
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### Multiplying Matrices of Vectors using Dot Product

I am given two 2D matrices where each of the cells is a vector with three elements. What I'm looking to do is use 2D matrix multiplication where when any of the cells are multiplied together, it ...
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### How to order a matrix by the numeric or alphabetic values of the column vectors in R?

The title with the following example should be self-explanatory: m = unique(replicate(5, sample(1:5, 5, rep=F)), MARGIN = 2) m [,1] [,2] [,3] [,4] [,5] [1,] 1 5 1 4 3 [2,] 5 ...
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### Any way of getting the canvas transformation matrix or at least the translation values?

I'm drawing in another view's canvas but I'm getting a translation. How to calculate or get the canvas translation if the method is deprecated? I'm drawing on the screen with a finger, but using ...
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### How to plot data as 2x 2 matrix

I have a short table includind three columns, two text columns (column 1 and column 2) and one numerical column. I would like to have a matrix / scatter plot (x and y as column 1 and column 2) and ...
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### How much space needed for a R matrix cell with 0 value? And how to deal with big matrix calculation

I want to calculate the correlation for a matrix, but stopped by program since the memory is not able to fit. M = matrix(0, length(user), length(mat)) when I run this line,I got a message ...
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### Correlation matrix of many variables (r and p-value)

I'm creating a correlation matrix for a very large database which includes 85 variables. My data contains missing values. So far I analyzed the whole DB, would you suggest to break it down in smaller ...
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### Remove negative part of the frequency spectrum after FFT operation

I have a matrix where I have performed an FFT operation, and I can view it using the imagesc function. However, I am seeing the negative spectrum as well, as shown in the figure below. The diagram I ...
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### MATLAB to convert xy plot to xyz array

I have a series of curves plotted in x vs. y format in MATLAB. I want to describe the shape they create at their intersection in an xyz format (a 2D array). There is no simple function in MATLAB to ...
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### Write a function given a zero-indexed matrix A consisting of N rows and M columns of integers, returns the number of equilibrium points of matrix A

Hey guys I am doing a question where I have to find a point in a Matrix A of N x M rows such that the sum of rows above the point is equal to the sum of row Consider this example /** * A[0][0] = 2 ...
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### Corrplot.mixed plot (number and square together)

Trying to put together the coefficient values (lower corner) and significance (upper corner) Try using corrplot.mixed but doing something wrong library(corrplot) library(Hmisc) mydata <- read.csv(...
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### Segmentation fault in creating a sparse matrix(Gallagers parity check matrix) [on hold]

I'm trying to implement the following: A matrix with binary entries alone, such that it has a fixed number of 1's in all the columns(wc) and also fixed number(wr) of 1's in all the rows. note: wr != ...
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### What is the rule behind the way singleton dimensions are squeezed in a submatrix?

It appears to me that MATLAB squeezes the singleton dimensions on the right-hand side of the last non-singleton dimension, with the restriction that a matrix must be at least two dimensional. ...
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### Getting weird output for dynamic allocation of the 2d array. How can I resolve the issue?

I want to create a dynamic 2d array and want to perform the operation on it. However, when I print the matrix, the first column shows different numbers, and don't know where is it coming from? I ...
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### How to reduce dimension of gene expression matrix by calculating correlation coefficients?

I am in interested in finding Pearson correlation coefficients between a list of genes. Basically, I have Affymetrix gene level expression matrix (genes in the rows and sample ID on the columns), and ...
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### How do I rotate a matrix 90 degrees counterclockwise in java?

I'm trying to go over the problems in the Cracking the Coding Interview book. One of the questions asks me to rotate a matrix 90 degrees clockwise. Now, while trying to solidify my understanding of ...
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### What is the Logic behind this matrix multiplication?

I am trying to multiply these 1 dimensional matrices( or vectors) with each other as follows : a = np.array([1,2,3]).reshape(1,3) b = np.array([4,5,6]).reshape(1,3) c = np.dot(a,b) print(c) ...
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### Indexing multiple array/ matrix elements similar to matlab “var[1:10]” in C

for my calculations i need to index into an array. I am used to MATLAB where you can index in a way such as var[1:10] // extracts the first through to the 10th element of "var" I am trying to find ...
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### How to find the reverse code of zigzag scanning of matrix using matlab?

I have an image and I want to encrypt it using zigzag scanning. I have a problem in the decryption because I need the code of the inverse zigzag scanning so I can restore the original image of 2 ...
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### How can I modify a 2d matrix so that predefined sums in both dimensions are satisfied?

I'm working on optimizing production of a number of related widgets over a number of weeks. The total quantity of each widget, and the total quantity of widgets produced each week is fixed. By ...