Questions tagged [octave]
Octave is a scientific programming & scripting language with syntax similar to MATLAB and SCILAB.
43
questions
3
votes
1answer
88 views
How can I extract the banded or block diagonal part of a sparse matrix in MATLAB?
Given a large sparse (square) matrix in MATLAB, how can I extract the banded or the block-diagonal parts (of fixed size) of it efficiently?
These are useful operations when prototyping and testing ...
0
votes
1answer
70 views
GNU Octave: using 'parallel' with an array (apply function to each array member)
I am new to GNU Octave 6.2.0 on Linux, and I am trying to use the package 'parallel' to make use of 24 threads on my machine.
I have an array (array1) that has ...
0
votes
1answer
41 views
Rem function in Octave showing wrong result
I am trying to write an if statement that checks if 2 numbers are divisible before running some commands. The problem is, the rem function is giving some wrong results for certain number (2 is ...
2
votes
1answer
125 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 ...
0
votes
1answer
32 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,...
1
vote
1answer
303 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^...
0
votes
1answer
135 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:
...
0
votes
1answer
90 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, ...
1
vote
2answers
199 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.
...
2
votes
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 ...
-1
votes
1answer
22 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....
1
vote
2answers
100 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 ...
0
votes
1answer
99 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. ...
0
votes
2answers
127 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} )$$
The intended result is:
However, using the following ...
3
votes
1answer
862 views
Finite difference method basic implementation on Octave
Trying to study the error of FDM for a second order derivative versus step size I calculated the coefficients and validated them, but the output has errors for small step sizes.
The function in ...
0
votes
1answer
66 views
Matlab struct vector
(I resume my question with a simple example)
I want to create a struct in matlab/octave as follows
c(1).x = [0 1];
c(2).x = [0 1];
...
c(100).x = [0 1];
...
1
vote
1answer
618 views
Plot 2D piecewise constant in matlab in a finite elements mesh
I need to generate a discontinuous plot (piecewise in each triangle) in matlab, something like:
This plot is from http://www.alecjacobson.com/weblog/?p=3616, but I don't understand how generate it.
...
1
vote
0answers
68 views
Is MATLAB feasible for app deployment versus lower level languages [duplicate]
MATLAB/Octave is a pretty useful language for prototyping scientific computation use cases, however I would like to know if the sheer nature of being a high level language bottlenecks how fast the ...
3
votes
2answers
5k views
BLAS libraries for Octave or Matlab, preferrably with GPU support?
I just searched around a bit for BLAS implementations and was amazed by the sheer amount of libraries around. Does someone know of a benchmark or otherwise rating of the various libraries?
How easy ...
0
votes
1answer
2k views
Solving Time dependent Schrodinger equation using MATLAB ode45 [closed]
The Schrodinger equation for time-dependent Hamiltonian is
$$i\hbar\frac{d}{dt}\psi(t) = H(t)\psi(t) \, .$$
I try to implement solve the Schrodinger equation for time-dependent Hamiltonian in ODE ...
2
votes
1answer
807 views
Defining Cauchy principal value in MATLAB (or Scilab/Maple)?
How to define a variable which is an integral involving cauchy principal value inside in any computer programming language? I want to know how to break down the procedure step by step from a ...
3
votes
1answer
335 views
Computational time not proportional to integration interval in ODE-solver?
I am running octave and i have been trying ode45, ode54, ode23 etc to integrate the equation `
$$Q''(t) = B\cos(Q)\sin(\omega t)$$
$$Q(t=0)=0.$$ When the time interval to be integrated increases, the ...
0
votes
1answer
249 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.
...
1
vote
1answer
130 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 ...
1
vote
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
votes
1answer
709 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 ...
1
vote
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, ...
13
votes
3answers
17k 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....
3
votes
1answer
2k 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 ...
1
vote
0answers
230 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 ...
2
votes
2answers
189 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:
...
1
vote
2answers
4k 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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0
votes
1answer
298 views
quiver3 gives non-conformant arguments?
Does anyone know why I'm seeing these errors? I'm not giving it a matrix.
...
19
votes
3answers
32k 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 <...
1
vote
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. ...
3
votes
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 - ...
8
votes
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
votes
1answer
4k 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
votes
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
votes
1answer
372 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 ...
7
votes
3answers
240 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 ...
12
votes
2answers
12k 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 ...
24
votes
12answers
20k 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 ...
