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# 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.

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### Generating a word bigram co-occurrence matrix

I have written a method which is designed to calculate the word co-occurrence matrix in a corpus, such that element(i,j) is the number of times that word i follows word j in the corpus. Here is my ...
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### Fast affine transformations of many 3D points by one 3×4 matrix

I wrote a function to batch-transform 3D vectors by a single 3x4 matrix using SSE2: ...
255 views

### Map square coordinates in matrix to flat array indices without hurting performance

I'm more like playing and the problem I'm going to demonstrate is a learning task, so to speak, not something I really need to solve. Imagine having a matrix of data. You chose square in it and ...
53 views

### Generate Orders from Matrix and save as CSV

I had a task to create a VBA macros which will take a matrix data set with products in rows and persons as a columns (on intersection we have an ordered qty for each material for each person) and ...
721 views

### Reading a CSV file containing a dataset of 8×8 images

I am trying to implement a machine learning algorithm (k-nn for example). But before I attempt to do that I was hoping for some feedback on my current Main class, which essentially builds 8×8-pixel ...
777 views

### LeetCode Minimum Path Sum algorithm

I am attempting to solve the Minimum Path Sum algorithm problem and I have a working solution, however there was an unwritten requirement that the algorithm not exceed an unspecified amount of time ...
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### 4D matrix math library for use with OpenGL

I am trying to create a simple library for C to handle OpenGL matrix operations. You can see the vec3fscalar here. ...
406 views

### Optimize matlab triple for loop

I have a large matrix samples, I want to make another matrix sampleProb which is the same size, but modified as below: ...
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### Searching for an element in a 2D array

For example, given a 2D array (a matrix): {{1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12}} What are the solutions to find a number, such as 6? Here's the code I ...
1k views

### Computing the sum of squared differences

About Data: 3D data (100x100x20). Computation/Formula and Method: I am trying to compute the sum of squared differences along rows, columns and angles for various time differences. ...
2k views

### Matrix bottom left to top right

Can someone please review this simple code for printing all paths in a matrix from bottom left to top right? If an element is 1, it is a "wall" and you cannot take it. Possible steps: up and right <...
97 views

### Fast matrix transpose

I would like to improve the naive matrix transpose algorithm by using a cache friendly algorithm. So far there are 4 variants. Iterate over the source matrix: ...
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### Stochastic gradient descent - backpropagation over mini-batches in one go

I have been working through a tutorial on neural networks. I have then been translating the code to java, to help improve my understanding of what the code is doing. The book mentions a way of ...
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### Convert a type u16 number to a matrix (Vec<Vec<u8>> or array) of 4 x 4

I am a Rust newbie and I am not familiar with all the iterator options. This is what I have so far. How can I make this better or at least avoid collecting twice into a Vec? ...
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### Extract numerics from matrix A with logical matrix B

I have a matrix A containing numeric values and a matrix B containing 0/1s: ...
876 views

### MIPS Assembly Program to access elements in the 4x4 matrix, row or column-major oder

This MIPS Assembly program will make you access the elements in the 4x4 matrix in either row or column-major order i.e. accessing all elements row by row or column by column. Output is posted below ...
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### Performing FFTW double on images of type cv::Mat

I've two different types of variables: cv::Mat and array of type double so I do quite lot of copying between the two types. I ...
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### product member of CSC matrix class

I'm implementing a CSR and CSC class! I found a lot of algorithms for computing a CSC * vector product but I didn't find any routine for the CsC * CsC matrix product, in order to save time when the ...
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### Parallel matrix multiplication in Java with streams

This StackOverflow post highlights how to do matrix multiplication using Java's stream. With Java streams, there is a new way to enable concurrent threading with the Java's parallel stream. ...
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This program is used to solve Challenge #140 [Intermediate] on /r/dailyprogrammer. The challenge is, given a input set of directed edges, print the corresponding ...
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### Blurring an image using matrices

Suppose there is a very big matrix and and a small window is moving on the matrix. The small window will move right and down, step by step (means each time move one step right, or move one step down). ...
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### Traceback in sequence alignment with affine gap penalty (Needleman-Wunsch)

I am working on an implementation of the Needleman-Wunsch sequence alignment algorithm in python, and I've already implemented the one that uses a linear gap penalty equation for scoring, but now I'm ...
127 views

### Cuda C Matrix Compression

I am using Cuda to learn and implement a CSR matrix compression algorithm. What can I do better relating to C's best practices? main.c: ...
397 views

### Get vertical acceleration from rotation vector and accelerometer values

My goal here is to calculate the acceleration towards the ground, which I call "vertical acceleration". This seems to be working OK for the most part, except when there is a lot of rotation going on ...
131 views

### Why does lu-factorization make my program slower?

I'm trying to calculate the smallest eigenvalue of the matrix A by using the "inverted exponentiation method" (see the code). I manage to find the smallest eigenvalue, but when I try to optimize the ...
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### Is my 4x4 matrix multiplication on a 1D float array correct?

I'm trying to develop my own math library to use on a Voxel engine, but I'm worried about Matrices multiplication. Everywhere I saw people using 4x4 Matrices on a 2D Float Array but I'm using a 1D ...
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### Matrix operations using classes

So I recently had a practical exam in which I was told to execute a function of a menu oriented matrix operation program using classes. The code I made was supposedly wrong as I hadn't used classes ...
201 views

### LSH hashcode generator function

For building an LSH based system in Python, I need to have a very fast calculation of the hashcode. I won't need to explain here the LSH algorithm itself, but I need help in improving performance of ...
892 views

### Effective Python 2/3 two-dimensional array initialisation

Recently I noticed that the idiomatic python two-dimensional array initialisation is extremely slow. I am wondering, is there a good, proper way of doing this simple task fast? Also, are those two ...
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### Matrix arithmetic operations

I am currently attempting to implement Matrix Math for another project I am working on. However, I am not sure whether this implementation will work. Can someone please tell me if there are any ...
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### Eigenvalue calculation for a Java matrix library [closed]

After an interview didn't go smoothly, I decided to write my own library so that I would be better prepared if I'm ever asked about matrix multiplication again. I know that doing it in Java is going ...
228 views

### Multiplication of 3×3 and N×N square matrices

I recently wrote a matrix module in C++. During the development process I quoted some source code and found a problem. For example, matrix multiplication: This way is suitable for all N×N matrices： ...
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### Multiplying two arrays

I would like to ask how I can make my code more simple and effective. I know that this code can be 100% better. I am supposed to load number for each array and then take the 2 arrays (4*3 and 3*4) and ...
240 views

### Drawing concentric circles to console

This prints out a triple layer circle with 12 points per circle and finds the points across a grid. I had a really hard time with this and I'm planning to implement a lot more code but I don't want ...
495 views

### Calculate median of a matrix

I am solving interview questions from here. Problem : Given a N cross M matrix in which each row is sorted, find the overall median of the matrix. Assume N*M is odd. Note: No extra memory is ...
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### Simple Matrix Rotation

I needed to rotate a non-square matrix in my program to transpose some spreadsheet data and decided to make a function to rotate 90, 180, or 270 degrees. It doesn't rotate the matrix in place, but ...
747 views

### Comparing rows of a matrix with some row vectors

I have run this program for five hours and it has not yet completed. I wonder if we can make changes to reduce the computation time. I use several for loop and this greatly increases the computation ...
178 views

### Clockwise rotate a matrix in Scala

Given a matrix, clockwise rotate elements in it. Examples: ...
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For my project in machine learning supervised, I have to simplify a training-data and I have to use this technique at page 5 of the document. Pseudocode algorithm My code (numbers are the steps): <...
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### Calculating shortest possible route between two given nodes

I recently came across this problem: Heroes in Indian movies are capable of superhuman feats. For example, they can jump between buildings, jump onto and from running trains, catch bullets with ...
91 views

### Code for number of routes possible of the given length between 2 given nodes

Recently I came across this problem , here is an excerpt of it, It is well known that the routing algorithm used on the Internet is highly non-optimal. A "hop", in Internet jargon, is a pair of ...
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### google foo.bar max path algorithm puzzle optimization [closed]

I got a programming puzzle described as follows: Save Beta Rabbit Oh no! The mad Professor Boolean has trapped Beta Rabbit in an NxN grid of rooms. In the center of each room (except for the ...
95 views

### C function for copying array into matrix

I want a matrix that can grow dynamically and build up a structure in RAM as input arrives from standard input och terminal (shell). First I tried with a matrix like ...
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### Simple implementation of nxn Dense Matrix in Java

So far this is what I have completed. Still working on these two methods boolean isIdentityMatrix(DenseMatrix matrix); boolean isInvertible(DenseMatrix matrix); Suggestions are appreciated. Thanks. ...
68 views

### Backward transformation implementation for a barrel eye lens aberration in c++ 14 (using opencv)

I've made the following backwards transformation from a "transformed" source x,y point, to the resulting index of the actual image that I have, so I can avoid black spots appearing in my barrel eye ...
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### Assign values to a matrix based on the location of non-zero elements in another matrix

I have a matrix, A containing ones and zeros. I want to create a new matrix B where the non-zero elements are in the same ...
79 views

### Find Row with Max zero

To find the row with max zero Matrix will have either 0 or 1 in sorted manner. ...
558 views

### Computing tangent space basis vectors for an arbitrary mesh

This is more like a share and a request than a question. I converted Eric Lengyel's code, which calculates tangents of a mesh for the purpose of texturing and normal mapping, to support SIMD. For this ...