Questions tagged [octave]

Octave is a scientific programming & scripting language with syntax similar to MATLAB and SCILAB.

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9 views

centering the y axis arrow [migrated]

I am currently trying to draw an oscillation using Octave. This is what I want to achieve in the end: In this diagram, the y axis arrow is drawn in the middle of the graph instead of at the top or ...
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1answer
109 views

(Lack of) Availability of Finite-Difference library for simple 2D PDEs

I would like to solve two types of simple 2D problems, namely the stationary heat equation on an L shaped geometry like this: And also compute the magnetostactic field in an air gap of the following ...
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1answer
29 views

Plotting two data sets in Octave

I have two data vectors $y1$ and $y2$, and I want to plot both of them as functions of the vector $x$. I want the result to be two overlapping curves. Here is the set of commands I am using. y2=[0.003,...
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1answer
139 views

Bode diagram without bode() function

Is there any way to make a bode plot without using the MATLAB/GNU Octave function bode()? As an example, here is a function I am working on: $$H(s) = \frac{1}{2s^...
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1answer
60 views

surface: rows (Z) must be the same as length (Y) and columns (Z) must be the same as length (X) in octave

I am having a dataset and trying to plot a 3-d plot between the independent and dependent variables.but, I am getting this error whenever I am trying to plot here is my code: ...
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1answer
85 views

Minimizing vector norm without using symbolic packages

I am new to octave and still learning what I can and cannot do with it. I am asked to write a following function ('trigmin'): [a, b, c, info]=tigmin(x,y) Where x, ...
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2answers
187 views

How to vectorize 2 nested for loop with one complex condition in the inner loop?

Octave calculations is too slow specially when you deal with scientific calculations that can span a very very large matrix, even just iterating. I have to vectorize it to speed up the calculation. ...
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0answers
74 views

Unforeseen behaviour of fix() in Octave and Scilab

I encountered some odd results when using the function fix() in Octave and Scilab. The following is input and output of the Scilab console but the exact same thing happens in Octave. I start with the ...
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1answer
21 views

Plot sinewave on ZX axis [duplicate]

I am trying to plot a sinewave with a bit of 3d perspective along the ZX axis instead of the XY axis. I have so far been unable to get anything that works, and have been unable to locate any examples....
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2answers
72 views

denoting a variable as a matrix using octave syms package

I'd like to use the syms package to do some algebra for me, but the baseline assumption seems to be that variables are scalars. I would like to denote some variables as matrices. This will change the ...
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1answer
95 views

How to write in paper the equations given by splinefit?

I am trying to write on paper the piecewise polynomials given by the splinefit function, but I am having some problems figuring out what the coefficients should be. ...
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2answers
117 views

Plot a multi-variable equation in (discontinuous) regions

The goal is to display the relation between K and E in the following equation: $$\cos(K) = 5 \text{sinc}( 5.12\sqrt{E} ) - \cos(5.12\sqrt{E} )$$ The intended result is: However, using the following ...
3
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1answer
753 views

Finite difference method basic implementation on Octave

Trying to study the error of FDM for a second order derivative versus step size I calculated the coefficients and validated them, but the output has errors for small step sizes. The function in ...
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1answer
65 views

Matlab struct vector

(I resume my question with a simple example) I want to create a struct in matlab/octave as follows c(1).x = [0 1]; c(2).x = [0 1]; ... c(100).x = [0 1]; ...
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1answer
576 views

Plot 2D piecewise constant in matlab in a finite elements mesh

I need to generate a discontinuous plot (piecewise in each triangle) in matlab, something like: This plot is from http://www.alecjacobson.com/weblog/?p=3616, but I don't understand how generate it. ...
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0answers
68 views

Is MATLAB feasible for app deployment versus lower level languages [duplicate]

MATLAB/Octave is a pretty useful language for prototyping scientific computation use cases, however I would like to know if the sheer nature of being a high level language bottlenecks how fast the ...
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2answers
4k views

BLAS libraries for Octave or Matlab, preferrably with GPU support?

I just searched around a bit for BLAS implementations and was amazed by the sheer amount of libraries around. Does someone know of a benchmark or otherwise rating of the various libraries? How easy ...
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1answer
2k views

Solving Time dependent Schrodinger equation using MATLAB ode45 [closed]

The Schrodinger equation for time-dependent Hamiltonian is $$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t) \, .$$ I try to implement solve the Schrodinger equation for time-dependent Hamiltonian in ODE ...
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1answer
743 views

Defining Cauchy principal value in MATLAB (or Scilab/Maple)?

How to define a variable which is an integral involving cauchy principal value inside in any computer programming language? I want to know how to break down the procedure step by step from a ...
3
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1answer
322 views

Computational time not proportional to integration interval in ODE-solver?

I am running octave and i have been trying ode45, ode54, ode23 etc to integrate the equation ` $$Q''(t) = B\cos(Q)\sin(\omega t)$$ $$Q(t=0)=0.$$ When the time interval to be integrated increases, the ...
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1answer
235 views

Nice plot of f(x)

A user has this nice graph of f(x) on his profile and I want to learn how to do it in matlab or Gnu octave. ...
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1answer
127 views

Applying a weighting function which is sampled at different points

I have a set of data to which I want to apply a weighting function, so basically a simple multiplication. My sampled data looks like this: (for those interested, it's the relative luminous intensity ...
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0answers
55 views

Software to simulate behavioral economic models?

I am looking for a way to simulate behavioral economic models to illustrate the effects of changing parameters. I am familiar with statistical analysis (especially R), but I only have few programming ...
2
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1answer
689 views

eigs routine in octave [closed]

I am using octave and observed a problem with the eigs-routine for non symmetric matrices. Using GNU octave version 3.8.1 the code below gives significant difference of eigenvalues although same ...
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1answer
2k views

Solve poisson equation with Neumann b.c. (matlab or octave)

I'm trying to reconstruct an image given its Laplacian, which results in a Poisson equation and I'm using Neumann boundary conditions (derivative at boundary = 0). What I have is the laplacian (f, ...
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3answers
16k views

Alternatives to Comsol Multiphysics

This might be a question better suited for the Software Recommendations side of S.E., however I do believe that people who frequent this part of S.E. are more likely to be able to answer this question....
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1answer
1k views

Partial differential equations with octave [closed]

I need to find a numerical solution for $-\Delta U = f$, on the $\Omega = [0,1]^2$, with $ U|_{\partial \Omega} = 0$. I found a method: POISSONFD in ...
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0answers
228 views

Printing a plot in Octave-3.8.1 breaks LaTeX labels [closed]

Since upgrading to Octave 3.8 I have been unable to export plots with LaTeX labels. When the figure is displayed the labels render fine but when I try to export the figure using the ...
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2answers
188 views

Solve chemical formula (number of molecules in reaction)

In order to balance atom count in chemical equation: a O2 + b C12H24O11 → c CO2 + d H2O I make linear equation: ...
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2answers
3k views

Polar axes in Octave?

if i draw a polar plot with Octave the axes are cartessian, not polar axes. But in Matlab it seems polar axes exists for polar plots. Is there anyway to draw with polar axes in polar plots in Octave? ...
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1answer
293 views

quiver3 gives non-conformant arguments?

Does anyone know why I'm seeing these errors? I'm not giving it a matrix. ...
19
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3answers
30k views

Euclidean distance in Octave

I would like to know if there is a quick way to compute the Euclidean distance of two vectors in Octave. It seems that there is no special function for that, so should I just use the formula with <...
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1answer
2k views

How can I get Octave to correctly compute a double integral of a piecewise function?

Computational Science People: The title is the question. I am trying to numerically compute a certain integral over a square in Octave (an open-source Matlab clone). I'm getting the wrong answer. ...
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2answers
4k views

Octave 3D mesh, data from file

I have a big file with 3 columns: density, dimension, value. example: 10 0.3 200 10 0.4 300 20 0.3 250 20 0.4 320 ... I am trying to draw a 3d plot - ...
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3answers
5k views

fmincg implementation in Python

I'm trying to re-implement Neural Networks in Python. I implemented the cost function and the backpropagation algorithm correctly. I have checked them by executing its Octave equivalent code. But ...
5
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1answer
3k views

Plotting x,y coordinates and vectors with octave

I have a data set containing the recorded data from a car's motion (latitude,longitude, and heading). I'd like to plot the (lat,lon) points on a 2D plot with a unit vector pointing in the direction ...
4
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1answer
1k views

Python syntax for MATLAB/Octave colon operator a:dx:b

I am trying to rewrite some MATLAB/Octave code in Python, and I don't know what would be the nicest or most intuitive way of writing ...
2
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1answer
357 views

In Octave, how do I specify that the solution to a matrix equation should be over integers?

In Octave, how do I specify that the solution to a matrix equation should be over integers? I.e., Given matrix $A$, vectors $x$ and $b$; $Ax=b$. Find vector $x=A^{-1}b$ such that all its entries are ...
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3answers
223 views

Converting from planar polynomial domain to planar polygon

Let's assume we have a planar domain whose boundary can be described with a polynomial curve (like Bezier curves). Now assume that you want to produce a discretization of the boundary, i.e. you want ...
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2answers
11k views

Octave: calculate distance between two matrices of vectors

Suppose I have two matrices Nx2, Mx2 representing N, M 2d vectors respectively. Is there a simple and good way to calculate distances between each vector pair (n, m)? The easy but inefficient way is ...
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12answers
19k views

Is it possible to use Octave to learn MATLAB programming?

I want to learn MATLAB programming so that I can conduct some researh/analysis on my own and also, so that I can study/modify some MATLAB scripts that I have found online etc. However, the problem is ...