# Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

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### How can I practice multivariable root-finding?

Recently, I've been reading up on various root-finding / optimization algorithms such as the Levenberg-Marquardt method, Gauss-Newton, Conjugate Gradient, trust-region and trust-region-dogleg. I've ...
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### ode15s command for coupled PDEs

I am trying to solve the coupled PDE system given here-Solve System of PDEs, using the method of lines and the ode15s command. Referring to variables $u1$ and $u2$ as $u$ and $v$ respectively, I have ...
153 views

### Two-dimensional modelling of a flate-plate reactor

I am trying to simulate the unsteady pollutant concentration along the reactor by solving the 2nd order PDE below with the stated BC and IC. which method is appropriate to solve convection-diffusion-...
43 views

### Finding isocontour lines, populating points on said lines (in MATLAB)

I'm trying to extract data from a potential field. I have an example code of a potential field, using meshgrid in MATLAB. I've pasted the code below. What I'd like to do next is 'convert' this field ...
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### How does Block-diagonal Schur factorization in Matlab works?

Can anyone explain how does the bdschur command of Matlab works? And how should the CONDMAX and ...
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### Inverse Newton Method for optimization: is this the correct algorithm?

I am trying to implement the algorithm in this article. I have already asked a question before about it here, and I am trying to figure out what I am doing wrong. This time, it's this section of the ...
72 views

### Using MATLAB to simulate the Ising Model

I am using MATLAB to simulate a 1D Ising Chain. I am running into an issue where when trying to find heat capacity, my system has a tremendous amount of noise. I'll post my code and an image of the ...
70 views

### Solving diffusion equation using finite difference method

I am solving an 1-dimensional diffusion equation with Neumann boundary condition at outlet and constant concentration, C, at the inlet. In the end, I want to observe how the concentration diffuses ...
362 views

### High-accuracy numerical differentiation

I have a $200 \times 200$ matrix representing the values taken by a function over an equally spaced grid. I would like to perform derivatives on it. I am interested in its gradient (i.e. its ...
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### Translating grid with extrusion speed

I am putting into MATLAB code the equations that describe a plastic extrusion process. From a paper, I found I should use a spatial grid that translates with the extrusion speed, being the reference ...
173 views

### Finite differences for the one-phase Stefan problem

I am trying to code the one-phase, one-dimensional Stefan problem using finite differences in Matlab, similarly to what has already been done in Mathematica (see https://mathematica.stackexchange.com/...
180 views

### Prescribing variables as an excitation in Runge-Kutta method

I am using Runge-Kutta to solve a $3 \times 3$ 2nd order linear ODE $$M x'' + C x' + K x = 0$$ and initial conditions are all zeros. Then I prescribe the 2nd variable to follow a given path. As for ...
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### scaling in discretized PDE system

I want to solve the following system via Matlab $\Omega=(0,1)^2$ $$\Delta y=\frac{1}{\alpha} p$$ $$-\Delta p= y -1$$ $$p|_{\partial \Omega}=0,~y|_{\partial \Omega}=0$$ using ...
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### Band structure of nonlinear Schrodinger equation with one dimensional potential

I have a nonlinear Schrodinger equation which reads: $$\frac{1}{2} \frac{d^2u}{dx^2}+ |u|^2u + V(x)u = -i \frac{du}{dz},$$ where $V(x)=\cos(wx)+ i a \sin(wx)$ and $w$, $a$ are numbers. How to ...
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### Solving HJ using Hopf-Lax formula (Burgers case)

Hi I want to approximate $u(x,t)$ solution of: $\begin{cases}u_t+H(u_x)=0 \\u(x,0)=u_0(x)= e^{−(x−3)^2} \end{cases}$, where $H(u_x)=\frac{u_x^2}{2}$ and my spatial domain is $\Omega=[0;10]$. Now i ...
1k views

Im currently implementing a Nelder-Mead algorithm in MATLAB that can deal with constraints. In detail, the constraints should be added to the objective function with a Lagrange Multiplier($\lambda$) ...
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### Adjoint of the MATLAB $\tt dwt3$ (3D wavelet transform) operator

How do I compute the adjoint of MATLAB's dwt3 operator? In other words, how do I compute the adjoint of the linear operator that takes a 3D complex array ...
70 views