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Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

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0answers
52 views

How to find the roots for this equation

I am new using Matlab. I am trying to find the roots for an effective permittivity equation in two forms: Quadratic and Nonlinear and it Should have the same solution. Any suggestion on how to solve ...
2
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1answer
60 views

Graphing electric potential of a ring of charge using MATLAB help

Here is a summary of what I am trying to do: Use MATLAB to compute the potential $V$ at any point $(x, y, z)$ in space due to a uniform ring of charge. Use a Riemann sum to compute the integral with ...
0
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0answers
23 views

Execution time of cumulative integral

In Matlab, we have the cumtrapz function, which returns the approximate cumulative integral of y: I = cumtrapz(x,y) This ...
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0answers
40 views

Computing Trajectory Equations of Kerr Geodesics

I want to numerically solve the trajectory equations of a Kerr geodesic given by wikipedia in Matlab. The trajectories look like: I implemented the equations and solved it with the standard Runge-...
0
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1answer
34 views

How to do Weierstrass-transform in MATLAB?

I have a diagonalization problem. I have the eigenstates correctly, and I want to do a Gaussian-smearing (Weierstrass-transform) on them. So I have the wave functions ($\Psi$), and the continuous ...
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0answers
21 views

Simulating Anderson model, have problem with momentum representation (MATLAB)

I want to change from real-space representation to momentum-space representation I have a Hamilton-operator (Anderson-model), and I calculated some kind of entropy of its eigenstates (this is working, ...
0
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0answers
25 views

Fit exponential convergence

I'm working with a numerical algorithm whose output $y$ asymptotically approaches a certain unknown value $a$. I expect an exponential convergence, i.e. the data $y$ given by my algorithm should be ...
0
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1answer
38 views

Monte Carlo - Random Walk Simulation - polyfit the log log data points?

This is part of the code in matlab for a random-walk simulation. To test the code, I'm using steps=[30]; there will be more values, but I want to run it for 1 trial to decrease code processing. <...
3
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3answers
318 views

How to assemble global matrix (for a coupled) problem?

I'm trying to assemble global matrices for the following system. $$ \begin{bmatrix} K& Q\\ Q^T&S \end{bmatrix} \begin{bmatrix} u_h\\ p_h \end{bmatrix} = \begin{bmatrix} f_u\\ f_p \end{...
2
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1answer
118 views

Correct Weights Neural Network

I'm trying to make a neural network using MATLAB. But I'm finding that many problems do not get solved. These are the formulas on which I based: $$ Layers\ in\ Neural\ Network = [0, ..., i, ..., out] ...
1
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1answer
54 views

Online Parameter Estimation using steepest descent

I have a first order system which is described by the following differential equation: dx/dt = -a*x + b*u where u is the input <...
0
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1answer
31 views

Plotting ratings matrix

Hello fellows and folks. I have been looking to do this for 1 month and still cannot find the way to do it. Here’s what’s going on: I have a csv file called ratings.csv with the following ...
1
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1answer
114 views

Use SLEPc from Matlab

Is there a direct way to use SLEPc from Matlab? I remember that in some old manuals there was some Matlab interface. However, in the last one, I cannot find any reference to this. For me, it would be ...
2
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1answer
206 views

Potential gain - Matlab vs C/C++ - assembly and eigenvalues

I have a Matlab code computing the solution to an eigenvalue PDE. It consists of two parts: assembly of the stiffness/rigidity matrices and solving a generalized eigenvalue problem. I mention that the ...
0
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1answer
140 views

Solving $n$ coupled equations numerically in Matlab

I would like to solve the following equations simultaneously and numerically for all $X, Y, Z, W$ where i = 1:Nw, j = 1:Nl, k = 1:K. $W_\text{net1}$, $W_\text{net2}...
1
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1answer
81 views

Name of third-party Matlab packages for solving PDEs

I am interested in working with systems of PDEs in two spatial dimensions, as part of a mathematical modeling project. The systems of PDEs are coupled, and there is no convenient reduction to 1 ...
2
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1answer
65 views

How to justify using available code (in different language) for comparing algorithms

I have proposed an algorithm for a scheduling problem in a submitting paper. In the revision, the reviewer asked us to compare with another algorithm from the literature. Our algorithm is in MATLAB, ...
1
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2answers
299 views

Can I model laminar incompressible fluid flow and heat transfer in MATLAB's PDE toolbox?

I have a system of PDEs in cylindrical coordinates that needs to be solved: 1. Continuity equation 2. Incompressible Navier stokes ( in r & z coordinates) 3. Heat transfer equation with both ...
0
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0answers
49 views

Solving a non-convex optimization problem using fmincon

I am trying to solve a non-convex optimization problem using fmincon(). At each iteration, I am iteratively looking for the optimum value and when the termination ...
1
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1answer
188 views

Efficiently generate a random subgraph (Gs) with maximum degree K, using only edges from an existing graph G

I am looking find a way of efficiently generating a random, undirected subgraph $G_s$ with $N$ vertices, using a subset of edges from an exisiting undirected graph $G$, also of size $N$, where the ...
0
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1answer
104 views

temperature profile on axial direction of a chamber

I have a task to plot average temperature profile at each cross-section in the axial direction of a combustion chamber. I have $x$, $y$, $z$ coordinates data in excel as well as the corresponding ...
0
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1answer
107 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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1answer
2k views

2D cross section from 3D surface

I am trying to apply the "restoring force surface" method to a dynamic linear system. The idea behind this method is that, knowing acceleration, displacement, velocity and input force it is possible ...
2
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0answers
28 views

ILUTP in sparse.linalg.spilu?

In Matlab, an ILU with threshold and pivoting (ILUTP) can be passed by default as: setup.type = 'ilutp'; [L, U] = ilu(A, setup); Looking for an equivalent in ...
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0answers
24 views

Cell-segmentation from overstaining images Ask [closed]

I am currently trying to segment cells from digital pathology images. The method I use is an algorithm based on color distance. This works for most of the cases, however, when dealing with the images ...
0
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0answers
33 views

Boundary conditions for solving the time-independent SE for the hydrogen atom

I am trying to solve the schrodinger equation for the hydrogen atom numerically, using finite elements, with matlab's solvepdeeig(). I have a hard time getting the solution to be right, and it seems ...
0
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1answer
76 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
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1answer
413 views

Finite Element Analysis for Laminated Plates with Holes or Patches

As the title says, I am trying to code in FEM a plate structure that either has a hole in one of the layers or one of the layers is made of patches of plates, rather than one whole plate. However, ...
1
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0answers
112 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 ...
3
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2answers
73 views

Efficient covariance matrix calculation MATLAB (every combination of rows from data)

My friend in the statistics department asked me how to do the following calculation efficiently. Suppose we have data $X\in\mathbb{R}^{N\times 2}$. He needs to do the following calculation: $$C_{i,j}=...
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0answers
16 views

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 ...
3
votes
1answer
201 views

MATLAB: Faber approximation of the matrix exponential to solve Liouville-von-Neumann equation

EDIT: I moved the full code to my github page so the post can be read more easily. I am writing a script to take the Faber approximation approach outlined in Hassan Fahs paper (free access) and apply ...
4
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0answers
68 views

MATLAB: Compute the Schwarz-Christoffel transformation symbolically

Suppose we have a conformal mapping from the unit disk in the $\omega$ plane onto the exterior of a polygon in the $z$ plane. The Schwarz-Christoffel mapping in this case is defined as: $$f(u) = A - ...
0
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1answer
274 views

Interior penalty discontinuous Galerkin Matlab implementation

I want to solve the 2D poisson problem using the interior penalty discontinuous Galerkin methods: −∇a(x)(∇u)=0 in Ω. The variational formulation is such that : $$a_{\epsilon}(u,v)=\sum_{K\in T_h}\...
2
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1answer
70 views

Eigenvectors associated to two quasi-degenerate eigenvalues

I need to find the smallest eigenvalue and the corresponding eigenvector of a sparse matrix $M$ whose dimension is $\approx 10^4$. Within Matlab enviroment, I use the command ...
3
votes
2answers
57 views

Finding exact rational solution to linear integer equations in Matlab

I have a linear system of equations $$Ax=b$$ where $A$ is an $N\times N$ matrix with integer values, and $b$ is a $N\times 1$ vector with integer values. Due to prior knowledge, I know that I am ...
0
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1answer
56 views

Finding Matrix inverse with LU and repeted left division calls

Hello I am in a basic numerical methods class and our teacher has given us an algorithm which can compute the inverse of a matrix other than using MATLAB's built in library function. ...
2
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2answers
152 views

Generate high n quantum harmonic oscillator states numerically

How can I generate the higher $n$ quantum harmonic oscillator wavefunction (in position space) numerically? Here, higher means around $n=500$, or say $n=2000$, where $n$ is the $n$th oscillator ...
2
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0answers
55 views

Unusual boundary conditions on Matlab

I'm trying to solve the following PDE by Matlab, $$ u_t-\Delta u = 0, \quad \text{in}\quad \Omega\times (0,T) \tag{1} $$ $$ u_t-\Delta_\Gamma u + \partial_\nu u=0,\quad \text{on}\quad \Gamma\times(0,...
11
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3answers
1k views

Least squares approximation question

I am taking a course on scientific computation, and we just went over least squares approximation. My question is specifically about approximating using polynomials. I understand that if you have n+1 ...
0
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1answer
94 views

coupled equations with finite difference method

I have these three differential equations in which I need to solve numerically: $$ \frac{dn_0}{dt}= -n_0(t)W_{01}(t) + n_1(t)K_{10} $$ $$ \frac{dn_1}{dt}= -n_1(t)W_{12}(t) - n_1(t)K_{10} + n_2(t)K_{...
5
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1answer
139 views

Matlab help related with the scaled Newton's iteration method

I need a little help with Matlab code for the method mentioned in this paper for computing the inverse of the matrix. In this paper, the author presented scaled Newton iteration given by $X_{k+1} = \...
2
votes
1answer
150 views

Analytical Solution of Transport Equation

I'm looking at the analytical solution of the convection-diffusion equation $$\frac{\partial C}{\partial t} = D\frac{\partial ^2 C}{\partial x^2}-v\frac{\partial C}{\partial x}$$ with initial ...
5
votes
1answer
9k views

How do I plot a transparent cylinder in matlab? [closed]

I know that I can use the following commands to create an opaque cylinder in matlab: N=100; [X,Y,Z]=cylinder(R,N); surf(X,Y,Z); I want to plot an arrow inside ...
1
vote
1answer
41 views

Wrong results for $2$ stage multistep method $y_{n+2} - y_n = h\left[(1/3)f_{n+2} + (4/3)f_{n+1} + (1/3)f_n\right]$

I need to fix a code to utilise the $2$ stage multistep method : $$y_{n+2} - y_n = h\left[(1/3)f_{n+2} + (4/3)f_{n+1} + (1/3)f_n\right]$$ Since this is an implicit method, I used a Newton-Raphson ...
2
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0answers
51 views

How to find two points within defined region in this constrained optimization problem?

I am doing a project related to robotics where I am using fmincon function from matlab to minimize the distance between the points ...
9
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2answers
205 views

Numerical stability of higher order Zernike polynomials

I'm trying to calculate higher order (e.g., m=0, n=46) Zernike moments for some image. However, I'm running into a problem ...
6
votes
3answers
251 views

Nonlinear eigenvalue problem - MATLAB code

I'm trying to solve a nonlinear eigenvalue problem in MATLAB, still without success. It's a problem about graphene plasmonics. The nonlinear eigenvalue problem is given below: \begin{equation} \frac{...