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Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

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10 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 ...
2
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1answer
59 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, ...
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1answer
124 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}...
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45 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 ...
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1answer
34 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. <...
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22 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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23 views

Cell-segmentation from overstaining images Ask

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 ...
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30 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 ...
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108 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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2answers
72 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
14 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 ...
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1answer
75 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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65 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 - ...
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1answer
193 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 ...
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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. ...
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2answers
56 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 ...
2
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1answer
67 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 ...
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0answers
52 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,...
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2answers
149 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 ...
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1answer
91 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_{...
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1answer
143 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 ...
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1answer
68 views

Stuck in infinite loop [closed]

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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 ...
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0answers
50 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 ...
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2answers
199 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 ...
3
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1answer
200 views

Step-size selection for an Trapezoidal Method ODE solver (ode23t)

I was reading the documentation of the MatLab ODE solver ode23t, and I've seen that the trapezoidal rule is used. Moreover, the error is estimated by ...
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0answers
94 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/...
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2answers
69 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 ...
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1answer
41 views

How do I find the default ODE solver tolerances in Matlab?

You can set the Absolute or Relative ODE solver tolerances in Matlab with the options structure from an odeset command. But how do I find the default values for the ...
2
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1answer
33 views

Log-transformation of decision variables in parameter estimation

I am trying to find the diffusion coefficient ($D$) and the partition coefficient ($KLP$) using experimental data of desorption of a pollutant from a film into a liquid. This process can be modelled, ...
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1answer
543 views

How does fmincon in MATLAB calculate gradients?

I am trying to solve numerically a constrained optimisation problem in MATLAB, and I am wondering how the fmincon function calculates gradients when one isn't ...
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1answer
117 views

Matlab parpool on Intel Xeon-Phi (KNL)

I am trying to run my matlab script on a Xeon Phi node with 68 physical cores. Using parpool I allocate 16 cores to enable SMD parallelization with a parfor loop. The script looks something like this. ...
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0answers
104 views

Accelerate computation speed by using a different syntax [closed]

I was reading a book about Matlab ("Accelerating Matlab with GPU computing - A Primer with Examples" by Jung Suh and Youngming Kim, 2013. Chapter 1.7 Examples). I read an example where it said that: ...
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3answers
240 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{...
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2answers
436 views

Matrix multiplication accuracy Matlab vs Python

I am translating some Matlab code into Python and I having some problems regarding matrix multiplication accuracy. Assuming we have following data: ...
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1answer
80 views

How to simulate thermal expansion in a 2D plane using FEA?

I am trying to model 2D thermal expansion of a square area inside another square using FEATool. I have simulated plane strain by incorporating forces pointing along the $[1 \,\,\, -1]^T$ direction ...
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1answer
106 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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0answers
101 views

Iteratively solving a sparse, ill-conditioned system

I have a sparse (density = 0.2%), ill-conditioned system that I am trying to solve, with no luck. Background I have a sequence of sampled data, where two of every 8 samples have been zeroed due to a ...
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1answer
81 views

System of ordinary differential equations - time complexity of initial value problem

I am interested in knowing what the time complexity is (in Big-$\mathcal O$ notation) for solving system of $N$ differential equations? I am using ode15s in ...
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0answers
108 views

Methods to implement floor dirt detection algorithm

I'm trying to detect dirty floor areas in a series of images, using MATLAB and its Image Processing Toolbox, like the one that follows: In the image above, there are two distinct areas, the whiter ...
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1answer
165 views

Discontinuous Galerkin - Inhomogeneous Dirichlet B.C. for 1D Poisson Equation

I am trying to get some code working for the 1D Poisson equation using the textbook: Nodal Discontinuous Galerkin Methods Algorithms, Analysis, and Applications. I use the following formulation (for ...
4
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1answer
58 views

How to preserve or recover states meanings in canonical state-space realizations

Let assume that one would like to translate an input-output model, into a state-space one. It is well-known that the process of realization addresses this aspect. Let assume to have the following ...
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1answer
104 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 ...
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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 ...
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1answer
99 views

Anyone who knows fine neural network code or module for python?

I want to change my main platform from Matlab to Python due to my work, and I mainly used Matlab for the neural network, so I want to do the same thing in the Python either. I used to make my own ...
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2answers
147 views

MATLAB Matrix Multiply Efficiency

I am using MATLAB to prototype a few matrix multiply techniques and compare efficiency. Eventually, I will move the prototype codes to C. It is for a homework assignment where we need to write an ...
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1answer
193 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 ...
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1answer
135 views

Finite difference method for the electric field of the electron gun

Can anybody help me to find books or MATLAB code examples for solving electric field of the electron gun(fig.1)with finite difference method? Python code examples are also perfect. The electron gun ...
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2answers
66 views

Finite difference for 2nd order ode $y'^2+y y''+\frac{2}{x} y y' -0.1 y^2=0$ with $y'(1)=0$ and $y(1)=1$

How to solve second order non-linear ODE $$y'^2+y y''+\frac{2}{x} y y' -0.1 y^2=0$$ subject to $y'(1)=0$ and $y(1)=1$ over the interval $0 < x \le 1$. I turned the equation to a PDE $y'^2+y y''+\...