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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0answers
313 views
Capture the notion of invertible functions
I find sometimes it is useful to capture the notion of invertible functions.
The idea is that if two functions f :: a -> b and ...
13
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1answer
132 views
Finding a zero crossing in a matrix
I am trying create an algorithm for finding the zero crossing (check that the signs of all the entries around the entry of interest are not the same) in a two dimensional matrix, as part of ...
11
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4answers
1k views
“Two-pass algorithm” implementation in Java
I'm rather new to Java and to algorithms in general. I implemented the so called Two-pass algorithm, and want to know if there are improvements to my way of implementing it. What it does is it takes a ...
11
votes
5answers
512 views
Set matrix zeros
I solved this problem in about 11 minutes (with all 50+ test cases passed).
I think most of you already know me by now, and I truly appreciate your advice, but please be brutal and judge me as if I ...
10
votes
2answers
399 views
Finding average of eight immediate neighbors of a matrix
I have this basic Java code to find average of eight immediate neighbors of a matrix.
Is there any way to simplify or merge any part of it, or can I refactor it?
I'm a beginner in Java programming ...
10
votes
3answers
333 views
Find biggest basin
Problem Statement
A group of farmers has some elevation data, and we’re going to help
them understand how rainfall flows over their farmland.
We’ll represent the land as a ...
10
votes
3answers
321 views
Row/Column Transpose
I was wondering if there is a smarter way of doing the following code. Basically what is does is that it opens a data file with a lot of rows and columns. The columns are then sorted so each column is ...
10
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1answer
547 views
10
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2answers
134 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
...
9
votes
2answers
224 views
Count the one islands in the matrix
What is an island?
A group of connected 1s forms an island. For example, the below matrix contains 5 islands:
...
9
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1answer
81 views
Gauss-Seidal implementation
The code is an implementation of the Gauss–Seidel method. I would like a general review of the code.
PS: I use code::blocks IDE
...
9
votes
2answers
263 views
C struct or pointer to struct?
I am currently using this code (and more) to deal with 2D matrices. I am not very proficient in C, so I am not quite sure, if this is a good way of doing it.
I've seen other people in similar ...
8
votes
1answer
165 views
10x10 bitmapped square with bits
This program prints out a 10x10 square and uses only bit operations. It works well, but I don't like that global array.
Can you tell me if the code is proper or not?
...
7
votes
2answers
202 views
Counting linear conflicts of the state of 8 puzzle for heuristic
I need to find linear conflicts of 8 puzzle state, state is represented by int[9], goal state is {1,2,3,4,5,6,7,8,0}. A linear conflict would be if in a line two ...
7
votes
2answers
708 views
Repetitive For Loops in 2048 Game
I have the following function defined in a program that implements the 2048 game. I tried condensing the repeating part of the code into one loop containing +1 offset variables for the indices, which ...
7
votes
1answer
296 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:
...
6
votes
1answer
74 views
Linear algebra, reduced row echelon form - function 1
This is a derivative post from here.
This is just a general review, so the question is the same:
Is there something...
That you would consider as a bad practice and why?
That is just bad in some ...
6
votes
1answer
618 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 ...
6
votes
1answer
70 views
Calculating Euclidean norm for each vector in a sparse matrix
Below is a naive algorithm to find nearest neighbours for a point in some n-dimensional space.
...
6
votes
3answers
54 views
Searching all diagonals of a 2D M x M array
I've started writing a piece of code to help me search for an object in all the objects found in the diagonals of an M x M 2D array.
Though the code works, I'd like to know if there is a way I can ...
6
votes
1answer
44 views
Average of positive and negative part of numpy matrix
I’ve got a matrix of data and I want to take the average of the positive and negative parts of the values.
Is there a more Pythonic way of doing it?
...
6
votes
1answer
419 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 ...
5
votes
3answers
78 views
More efficient (or correct) way to make image grouping work?
It might be easier to read the explanation of what I was trying to do, and implement it a completely different way, rather than go through the code. But the code does what I want it to do, just ...
5
votes
2answers
1k 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 int[16]s.
...
5
votes
2answers
134 views
Calculate fibonacci in O(log n)
This program calculates the \$n\$th fibonacci number, in \$O(\log n)\$ time. I'm looking for code review, optimizations, and best practices.
...
5
votes
2answers
261 views
Fixed size matrix implementation
I implemented a fixed-size matrix class which supports basic matrix operations (cannot use C++11). What do you think, and how could it be improved?
...
5
votes
2answers
52 views
Increment the cells around one in a matrix
Let's say you want to increment the cells around the position (x,y) in a square matrix m of size ...
5
votes
1answer
80 views
In 8-puzzle finding nr of steps moving a tile to the right place
In 8-puzzle I want to count the number of moves it would take to move a specific tile to it's goal place. The problem is my method for this is >100 lines long which is obviously way too much. I'll ...
5
votes
1answer
100 views
Optimizing multiplication of square matrices for full CPU utilization
Cross-post from Stack Overflow since this is very code intensive
Problem
I am learning about HPC and code optimization. I attempt to replicate the results in Goto's seminal matrix multiplication ...
5
votes
2answers
82 views
Optimizing garbage collection for local objects
I am trying to make a 3D application with OpenGL/LWJGL at the moment, but I am now already hitting some limits on the JVM, most likely due to a configuration that needs to be done.
I have the ...
5
votes
1answer
81 views
Linear algebra, reduced row echelon form
The code that I am sharing here for you to review today, is a segment of a JavaScript library that I am going to write as time goes by for fun. It is only the two functions in the following code:
...
5
votes
1answer
107 views
Searching in a sorted 2D matrix
If I was at an interview, and wrote this code, what would you think? Please be brutal.
Time it took to wrote it: 13 minutes
Problem:
Write an efficient algorithm that searches for a value in an ...
5
votes
1answer
57 views
Orchard Partitioning in to close-to-equal sectors
The task (from this site) is to create a program that will solve a problem where a matrix (size n * n), which contains integers, is to be divided into four parts, the sums of which are as close to ...
5
votes
2answers
131 views
Defensive programming type-checking
I have issues with dynamically typed languages, and I tend to worry about type a lot.
Numpy has different behaviour depending on if something is a matrix or a plain ndarray, or a list. I didn't ...
4
votes
2answers
477 views
Rotate an image by 90 degrees
Looking for review, good practices, optimizations, clean code tips etc.
...
4
votes
1answer
56 views
Performing a special multiplication on two square matrices
I have a function called mult2 that takes in two square NumPy matrices and returns a matrix that is the result of a special multiplication:
...
4
votes
1answer
328 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| + ...
4
votes
1answer
592 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 ...
4
votes
1answer
84 views
Optimize vector rotation
I have a trivial function that rotates 2d vectors, and a method in a class representing a polygon that rotates every point in the polygon around an origin. The code is fairly optimized as it is, but I ...
4
votes
1answer
52 views
Matrix rotation efficiency
I am not sure if I should be using recursion or not or if it even helps in increasing the performance of my algorithm. I feel as though I am creating and replacing too many arrays by calling my inner ...
4
votes
1answer
128 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 ...
4
votes
2answers
1k 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 ...
4
votes
1answer
55 views
Optimization of matrix determinant calculation
I have this algorithm that calculates the matrix determinant using recursive divide-and conquer-approach:
...
3
votes
3answers
204 views
Simple matrix class - version 2
As suggested on my previous question, I am posting my revised code for feedback.
One thing that caught my attention is that my program actually runs slower after adding the modifications. It was ...
3
votes
2answers
402 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 ...
3
votes
5answers
313 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.
...
3
votes
2answers
93 views
Path from source to destination, with increasing values
Given a source and destination, in an integer matrix, find path, such
that the next position in the path has a greater than or equal to
value than the previous position. In other words ...
3
votes
2answers
42 views
Implementing Transpose
I'm implementing transpose in Haskell.
-- transpose [[1,2,3],[4,5,6],[7,8,9]]
-- [[1,4,7],[2,5,8],[3,6,9]]
Please give it a ...
3
votes
2answers
322 views
Find mirror image of a matrix
Looking for review, good practices, optimizations, clean code tips etc.
...
3
votes
1answer
74 views
Point in a polygon algorithm
I am implementing a Point in polygon algorithm.
Inputs:
M, N: size of the matrix
poly: a ...
