# Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

600 questions
67 views

### Solving for $C$ in $Q = YCZ$ using least squares in Matlab

I am trying to solve for the matrix $C$ in $Q = YCZ$ in matlab. I have preliminary results but they don't seem realistic. Here, $Q$ is $n \times m-1$, $Y$ is $n \times p$, $C$ is $p \times m$ and $Z$ ...
133 views

### Derivatives of a Chebychev polynomial

I am using Chebychev collocation nodes for approximation, and my problem requires me to calculate derivatives of the polynomial. I have been reading from a few sources, but I am not sure I understand ...
188 views

### Adding Non-Linear source term to 2d Implicit MATLAB code

I'm running out of time for this code so any help would be greatly appreciated. I am currently coding the 2D heat/diffusion equation in matlab but i'm having trouble adding in the source term. my ...
219 views

### Modelica and SIMULINK yield completely different results

I'm trying to simulate a 1D model of two bodies sliding on each other with a Coulomb friction in between. As I have explained here I modeled the friction as : The force required to keep two bodies ...
286 views

### Is the exponential function, e^x, very expensive to compute in Matlab and harmful to my computer?

Is the exponential function problematic and very expensive to compute in Matlab? When I write a new term for my model of ODEs that has an exponential term in it, the program almost never finishes ...
190 views

### In Matlab, how can I be consistent with units?

I am modeling some aerodynamics equations and am using meters / centimeters, kilograms, and seconds. I've heard that, "matlab doesn't know units". So, how can I make sure that it does? Just ...
222 views

### Writing a programming code directly from the mathematical formula?

For using any programming language, a mathematical formula should be written in the corresponding code. I wonder if there is any service (for any programming language, Matlab, Mathematica, Python, etc)...
191 views

### How to compute the Frobenius norm of matrices whose entries are either too large or too small?

While implementing in Matlab the Frobenius norm of a matrix $$\| A\|_{\text F} := \sqrt{ \sum_{i=1}^m \sum_{j=1}^n a_{ij}^2 },$$ a problem arises when numbers are too big or too small: If a number ...
339 views

### Numerical propagation of a density matrix using Liouville von Neumann equation

I want to look at time evolution of the density matrices of some, very simple, spin systems, but I am having trouble with my approach. I want to use a simple for-...
38 views

### Plotting using 'colorbar' in MATLAB [closed]

I am trying to plot a figure similar to the one attached here,I tried searching how to do a similar kinds of plot and i found about 'colormap','colorbar' in MATLAB. Actually I want to plot this ...
182 views

### Create mesh for complicated 3D object for finite element analysis

I see images of steel connections, concrete dams, and other complicated 3D objects in papers which finite element analysis has been performed on them. My questions are: How these objects are created ...
122 views

### Computing Eigenvectors in MATLAB

I am assigned to compute eigenvalues and eigenvectors in MATLAB of a 2x2 matrix: $$A = \left( \begin{matrix} 3 &0\\ 4 &5\\ \end{matrix} \right)$$ I know that the textbook's solution states ...
61 views

### Non linear programming solvers with API for MATLAB?

I'm facing a non-linear programming problem which currently I'm solving with fmincon function of MATLAB. However, I'm not very happy with computation times and solution convergence since it only ...
256 views

### Kronecker product among multiple arrays

I was wondering whether there is a smart and efficient way in Matlab to compute the kronecker product of several 1D arrays. What I mean is something like this ...
87 views

### finding the growth rate from numerical data

Suppose i have a bunch of 10 data points and i have to conclude whether the increase is $n^2,n^3,\cdots,2^n,3^n, e^n,\cdots$. For example i have the image:- Now the increase is either polynomial or ...
345 views

### Complex Eigenvalues using eig (Matlab)

I wanted to find and plot the eigenvalues of large matrices (around1000x1000). But discovered when using the eig function in matlab, it gives complex eigenvalues when it shouldn't. For example, in the ...
80 views

### Precision not improving by decreasing step-size in nonlinear Schrödinger

I tried to simulate soliton propagation by solving the nonlinear Schrödinger equation using the split-step Fourier method. The following is an example of the Matlab code copied from a textbook. ...
41 views

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### Vectorizing Matrix Multiplication

I would like to do the following operation: I have a "4D" matrix A and a "3D" matrix B. Both A and B are actually 2D matrices, where for A, each element is a 2D matrix, and for B, each element is a 1D ...
28 views

### Pseudo-Spectral cosine transform

I'm trying to solve the following equation $$u_t = u_{xx} + u(1-u^2), u_x(\pm 1) = 0,$$ using the Fourier cosine transform. The nonlinear term gives a convolution which I would rather avoid, which is ...
104 views

### Second Quantization in Matlab

This question may be more suited for physics.stackexchange, but I saw this post was recommended for StackOverflow or Computational Science, so I'm asking my question here. I am trying to write a ...
66 views

### Approximating derivative of numerical solution (using ode45) within event function

The issue I have is having to compute the derivative (in real time) of the solution produced by ode45 within the events function. Some pseudo-code to explain what I'm mean is, ...
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### Accuracy of finite difference method for heat equation on a disk

To study an approximation for the heat equation $$\frac{\partial^2 u}{\partial r^2}+\frac{1}{r}\frac{\partial u}{\partial r}+\frac{1}{r^2}\frac{\partial^2 u}{\partial\theta^2}=f(r,\theta)$$ on the ...
140 views

### Solving optimal control problems using third-party NLP solvers

I've been doing a bit of work on the so-called pseudospectral optimal control for trajectory optimization of a launch vehicle into orbit. However, comparing my results to the literature, I seem to be ...
51 views

### Calculating a limit as parameter goes to infinity

I have a fair background in pure mathematics and right now my project is a numerical implementation of a certain algorithm. I have some numerical background, but not all that much, so the question is ...
308 views

### How accurate is cumtrapz in MatLab?

Say I have a set of discrete acceleration data and want to integrate it to get a set of velocity data. How accurate is the cumtrapz (Cumulative trapezoidal ...
882 views

### Multiplying two functions in MATLAB

I want the product of two functions $f(x),g(x)$ $$f(x) = x + \sin(x)\\ g(x) = x - \sin(x)$$ then $$f(x)g(x) = x^2 - \sin^{2}(x)$$ How could I compute the product of two functions?. I tried ...
394 views

### Numerical implementation of the Dirichlet-to-Neumann map

I am solving the Dirichlet problem $$\begin{cases} \Delta u = 0, \\ u|_{\partial D} = f, \end{cases}$$ in a $2d$ domain $D$ using the finite element method. What I want to get is the ...
175 views

### 4D visualization in MATLAB

I have a function of 3 variables like $V= f(r1,p,r2)$, I want to plot these 4 data in one graph to be able to capture behavior of V with respect to all three variables. I searched a little bit and ...
158 views

### Solid volume calculation

In order to calculate the volume of the solid defined by $$\frac{51}{100} (\cos x \cos y+\cos x \cos z+\cos y \cos z)+\cos x+\cos y+\cos z+1\le0$$ where $x,y,z\in[0,2\pi]$ I used the following code ...
296 views

### 2D simulation of a particle with different diffusion coefficient in different directions of the particle

How can one simulate diffusion of a particle which has a natural axis and diffusion coefficient of the particle in the direction of the axis is D_1 and in perpendicular to the axis is D_2? Could ...
51 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]; ...
285 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. ...
74 views

### Composite Laminate Mass Matrix Help

So, as the title of the post implies, I'm making an FEM code for a composite laminate plate using the Mindlin plate theory. And, as I am trying to get the mode shapes for the plate, I needed to make a ...
423 views

### Position Estimation using 2D multilateration for non-intersecting distances

I am trying to estimate the position of a point $P$ in Matlab. I have $n$ access points (AP) at known positions ($n>2$) as well as the distances to the point $P$ from each AP. These distances all ...
1k views

### How to compute the Helmholtz decomposition of 2D and 3D vector fields?

I have a sample of 100 particles with their 3D positions and velocities. I want to decompose the velocity vector field to its curl free and divergence free components. Is it a feasible to do so for ...
205 views

### MATLAB: solving multiple ODE systems in parallel

I have a system of parameterized ODEs that I would like to solve using MATLAB and its ode45 solver, and was wondering if it is possible to perform such a task in ...
318 views

### How to implement an integral condition when solving a BVP in MatLab

I am trying to solve a coupled system of ODE's using MATLAB's bvp4c function. I want to impose the condition that $$\int_{0}^{\pi} y_{1}(t) y_{1}(t) dt = 1,$$ where ...
119 views

### Estimate $L_2$ norm of a elliptic problem with unknown exact solution on finite element method

I have the elliptic problem $$-\Delta u = 1,\,\,\Omega\subset\mathbb{R}^2$$ with $u=0$ on $\partial\Omega,$ with $\Omega=[-1,1]^2\backslash([0,1]\times[-1,0])$ and I want to estimate the $L_2$ error ...
2k views

### What is the difference between MATLAB and FORTRAN?

In our university some Ph.D students for computational methods prefer FORTRAN over MATLAB. I can't understand why? What is the difference between them when are used in computational methods like ...
139 views

### Trouble getting steady-state solution by solving system of nonlinear algebraic equations in MATLAB

Background I have a stiff system of 6 ODEs, represented in MATLAB as follows: ...
216 views

### Random walk on lattice

I have a $9 \times 9$ square lattice. In each site of the lattice, there are $N$ molecules, where $N$ is a large random number and it is different for different sites. N equal to 100000000+-100 in ...