Questions tagged [matlab]

MATLAB is a high-level language and interactive programming environment developed by MathWorks. It is the foundation for a number of other tools, including Simulink and various toolboxes that extend the core capabilities.

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130 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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1answer
57 views

Less For, more MATLABesque?

I have written a piece of MATLAB code that (hopefully) calculates CECT. I have two matrices of psychophysiological measures - one for brain data, one for heart rate; both are of the format epochs * ...
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1answer
78 views

Using the Return Value of a Function to Select an Element in a Struct Array

I'm learning MATLAB (still trying to "think in vectors") and have the following piece of code: ...
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2answers
417 views

Creation of MxM matrix: Python version much slower than Matlab version

I have written the same code in Python (NumPy) and in Matlab, and I tried to use the same structure for both language and follow the same procedure. Now my problem is that when I run my code in Python ...
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1answer
2k views

Stochastic gradient descent squared loss

I have implemented stochastic gradient descent in matlab and I would like to compare my results with another source but the error I am getting is higher (I am using squared error). I am worried I am ...
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1answer
26k views

K-nearest neighbours in MATLAB

I implemented K-Nearest Neighbours algorithm, but my experience using MATLAB is lacking. I need you to check the small portion of code and tell me what can be improved or modified. I hope it is a ...
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1answer
2k views

Parsing MWNumericArray to C# code optimization

This is my function returning matrices from Matlab. This code run very slowly. I was trying to use Parallel.For in-order to run it in parallel threads but I got ...
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0answers
117 views

Increasing speed of parity check matrix

The code runs fine and takes 100s to complete it for 5 iteration. I need to reduce it to take less time with the same number of iterations. h = 324 by 648 matrix The code is that of FFT Belief ...
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2answers
88 views

What's the fastest way to get the points I want out of a huge blob?

In MATLAB I have a set of 5393280 points in the form of a decimal-valued vector (x,y,z). How do I represent them in a way that I can quickly collect all the points within some rectangular x-y domain? ...
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1answer
99 views

Downloading the oldest available version of some data files

I am using the cURL tool in MATLAB 2013b with Ubuntu to download a whole bunch of files. The files have one of three possible versions: 1.0.0, 2.0.0, or 2.1.0. Using the HTTP, I first check the ...
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3answers
5k views

k-nearest neighbors using MATLAB with MEX

I have implemented kNN (k-nearest neighbors) as follows, but it is very slow. I want to get an exact k-nearest-neighbor, not the approximate ones, so I didn't use the FLANN or ANN libraries. ...
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3answers
105 views

Is this a valid way of computing autocorrelation?

I am a beginner in Digital Signal Processing and I was trying to compute and plot an autocorrelation. I've wrote this piece of code: ...
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1answer
86 views

Speeding up repetitive initialisation with structured data?

I need to speed up this code: it creates a multilinear function. I considered the below methods but no idea which with the largest benefit. replacing dummy variables with things such as anonymous ...
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0answers
95 views

Fitness function

I have a fitness function, where inputs x1 to x14 have values between 1:4. Is there a way to make this more efficient? Any ...
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3answers
106 views

Using matlabpool: Is my embedding correct?

A general question: For using matlabpool, I write the line matlabpool open local 12; as the first line in my code and the line: ...
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1answer
2k views

Matlab - Fastest way to parallel read many files line by line?

I have a few hundred files in a directory that I need to read in parallel. Namely, the files that have the same name, but different file extensions (.a and .b), but they're pretty much plain text ...
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2answers
1k views

Rational Approximation for e with Matlab

I've written a program that calculates the best rational approximation for e with a 1, 2, 3, 4, 5, and 6 digit denominator respectively (on Matlab). For a 5-digit denominator it takes about a minute. ...
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1answer
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, ...
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2answers
204 views

Calculating the posterior distribution in multivariate Gaussian processes

Matlab profiler throws this horrible bottleneck which is called 700000 times: ...
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1answer
7k views

2D convolution in matlab

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2answers
4k views

Python / Numpy running 15x slower than MATLAB - am I using Numpy effeciently?

Here is some code I wrote in Python / Numpy that I pretty much directly translated from MATLAB code. When I run the code in MATLAB on my machine, it takes roughly 17 seconds. When I run the code in ...
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2answers
1k views

Drawing random smooth lines contained within a square

I'm trying to write a matlab function that creates random, smooth trajectories in a square of finite side length. Here is my current attempt at such a procedure: ...
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1answer
2k views

Using homogeneous coordinates to rotate an image

Currently, I have this code snippet, but it's a little bit slow: ...
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1answer
231 views

Getting B+ matrix (Warshall algorithm) in Matlab

Pseudocode: ...
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1answer
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: ...
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1answer
217 views

Calculate FFT from windowed time-based signal

I have a time-based signal (Raw signal) sampled at 6 MHz and need to analyze it in freq. domain. I'm learning DSP and this is very first time I work with DSP. Could you please help to check if this ...
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1answer
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. ...
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1answer
322 views

Is this a valid usage of structure assignment in C?

Q: Please comment on the usage of structures and structure assignment operations in C I am working on converting a MATLAB program to C using BLAS and LAPACK for linear algebra support. The MATLAB ...
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2answers
2k views

MATLAB and Armadillo, hints on translating

i'm rewriting some Matlab code to c++ using armadillo, a libs for linear algebra. really good libs, IMHO. but i had to translate some matlab construct because armadillo isn't matlab. i want to share ...
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1answer
1k views

Generate graph in Matlab

I use this Matlab code: ...
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1answer
13k views

Matlab code demonstrating use of fft (Fast Fourier Transform)

I posted the following Matlab script in response to a question on Signal Processing. Here is the questions with my answer. I am looking for comments on how to make this code more instructive for the ...
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1answer
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 ...
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1answer
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: ...
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1answer
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 ...
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1answer
185 views

Creating a matrix from a dyadic product

Ax, Ay, Az: [N-by-N] B=AA (dyadic product) means ...
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1answer
1k views

Legendre's polynomials and functions

I would like to improve this function to reduce the run time and optimize it. ...
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1answer
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 ...
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3answers
493 views

Presidential election predictor using matrix-processing

I'm currently working on a project where I am trying to predict a presidential election based on the population density and region of a voter. I wrote a few MATLAB functions to parse the data, but it ...