# 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.

543 questions
Filter by
Sorted by
Tagged with
3k views

### Build a combinatorial matrix from two vectors

I want to define a matrix of values with a very simple pattern. I've achieved it with the code below but it's ugly - very difficult to read (I find) and surely not as optimal, in terms of performance, ...
3k views

### Generating adjacency matrix on random cout of graphs with output the matrix

I've developed program, which may work with graphs and its edges (connections between vertices): http://ideone.com/FDCtT0 ...
2k views

### Sparse matrix multiplication

I am working on a sparse matrix application in C and I choose compressed sparse row (CSC) and compressed sparse column (CSC) as my data structure for it. But the difficult part is I cannot improve my ...
5k views

### 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 ...
2k views

### Implementing the CutHill-McKee Algorithm

I am very much interested in the Reverse Cuthil McKee Algorithm. I have seen Fortran and C or C++ implementations of it, and I decided that it would be a nice exercise to implement it in Python. I ...
1k views

### Golang solution to Project Euler #81 (min path through a matrix)

Project Euler problem 81 asks: In the 5 by 5 matrix below, ...
446 views

Can anyone review my addMatrix() method to see if I am following the instructions correctly? These are the instructions: This is a ...
2k views

### The number of connected component

Compute the number of connected component in a matrix, saying M. Given two items with coordinates [x1, y1] and [x2, y2] in M, if M(x1, y1) == -1 and M(x2, y2) == -1 and |x1-x2| + |y1-y2| ...
98 views

This is what the code should do: Check if the first dimensions and the second dimensions of each 2-dimensionalarray are the same. If they are not the same, then return a 0x0 2-dimensional array. ...
168 views

### How to increase efficiency of matrix operation in C?

I have a N*N upper triangular matrix with property such that, all its diagonal elements are a1,a2,a3,...,aN. I want that a[i][j] (for all j>i) should be ...
194 views

### Outputting a 2^n x 2^n matrix

I've written a simple program in Python which does the following: Input: an integer $n$ Output: a $2^n x 2^n$ matrix containing small $L$s which fill the entire matrix except one single square....
2k views

### Using homogeneous coordinates to rotate an image

Currently, I have this code snippet, but it's a little bit slow: ...
231 views

Pseudocode: ...
169 views

### Processing random matrices

I am doing my research about scheduling by using Matlab. I am a new Matlab user and I have a problem with time execution of my following code: ...
297 views

### Devise an algorithm of complexity O(N) finding No of 1's from a 2 dimensional matrix[N][N] containing 1's and 0's

Assume a 2D [n][n] matrix of 1's and 0's. All the 1's in any row should come before 0's. The number of 1's in any row I should be at least the number of 1's row (i+1). Find a method and write a C ...
508 views

### Optimizing code from spectral subtraction algorithm

This is part of the code from a spectral subtraction algorithm. I'm trying to optimize it for Android. Matlab code: ...
3k views

### Templated Matrix class

I created a Matrix class. I tested it and it seems to work. Can someone tell me if this class is good? Can I improve it? Can I use more move semantics (where)? What do I have to modify? Are there ...
359 views

### Producing a matrix class that supports any size

I'm doing exercise 11.8 from Scala for impatient, asking to write a matrix class: Provide a class Matrix - you can choose whether you want to implement 2 x 2 ...
2k views

### Finding the largest product of four consecutive numbers in a grid

Project Euler #11 asks to find the largest product of four numbers of a grid, where the four numbers occur consecutive to each other vertically, horizontally, or diagonally. Here is my solution in ...
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. ...
3k views

### Element-comparison NumPy matrix

I need a NumPy matrix with comparisons among all elements in a sequence: ...
154 views

### Updating a density distribution

I am running a Markov Chain Monte Carlo algorithm for updating a density distribution. There is a specific section of my code which tries to fill a very large matrix ...
1k views

### Path sum - Dijkstra's algorithm in F#

I'm learning F# and I've decided to solve Project Euler's Problem #81 with Dijkstra's algorithm. In the 5 by 5 matrix below, the minimal path sum from the top left to the bottom right, by only ...
159 views

### Attempting to eliminate var (and imperative style) from my Piece class

I've been cooking with gas since I got Daniel C Sobral's help on my last question. I am now re-reading Odersky's "Programming in Scala, 2nd Edition" (finished my first reading about this time last ...
273 views

### Computing a Discrete Cosine Transform matrix

I'm learning Haskell and I needed to work with discrete cosine transform matrices, so I made a program that generates text (usable in WolframAlpha) containing the generated matrix. The elements of ...
4k views

### Implementation of Mahalanobis distances using Eigen

I'm trying to learn C++ with Eigen. Here's my attempt at computing Mahalanobis distances of a set of points x with respect to a sub-matrix ...
473 views

### High performance exponential of a skew Hermitian matrix in Fortran 95

I'm new to Fortran, and this is pretty much my first escapade. Below is a function that I wrote which relies on calls to LAPACK. The function is sat in a module with some other functions and works ...
8k views

### Am I multiplying two matrices together correctly?

I just wanted to know if I'm doing this right. Note that all the matrices are ints. ...
471 views

### Finding columns of a matrix that are the same for combinations of events

How I can change this multi-loop to reduce the computation time? A is a matrix (5 × 10000) where the fifth line contains values between 1 and 50 corresponding to ...
288 views

### Eliminating columns from a matrix where the entries in two rows are equal

Is there a way to reduce the computation time in this program that eliminates the columns of a matrix A if for a given column the element of line 4 is equal to the element in row 5: ...
746 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 ...
461 views

### Back propagation neural network

This is the first time I tried to write a back propagation ANN and I would like to know what more experienced people think of it. The code is meant to distinguish if text is written in English, French ...
532 views

### Transpose a matrix using sed

I'm trying to transpose the following data from: ...
1k views

### Fill upper triangular matrix from a list

I am looking a good way to fill up the elements of a lower triangular matrix from a list. I currently have this: ...
2k views

### STL matrix chain multiplication

Please provide positive and not-so-positive feedback on style, clarity, or any other additional feedback you would like to provide. ...
1k views

### Determine if an element exists in a sorted NxN matrix

The point of this algorithm is to see if an element exists in a NxN matrix that has its rows and columns sorted. What would you change? What did I do well? Both perspectives help so I am not left ...
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 <...
185 views

### Creating a matrix from a dyadic product

Ax, Ay, Az: [N-by-N] B=AA (dyadic product) means ...
2k views

### Finding the maximum row of a 4x4 matrix

I have written a recursive function that I believe will return the 'maximum' row of the 4x4 matrix it is fed. By 'maximum' I mean that the maximum row of the matrix. ...
333 views

### Set of linear equations

I have $N^2$ matrices. Each one is a $3 \times 3$ matrix. I want to concatenation them to a $3N \times 3N$ matrix. I know that the big matrix is symmetric. Evaluation of whole \\$ 3 \times ...
4k views

### Matrix multiplication and dot-product

Exercise 2.37. Suppose we represent vectors v = (vi) as sequences of numbers, and matrices m = (mij) as sequences of vectors (the rows of the matrix). For example, the matrix is ...