Tagged Questions

Questions about the numerical programming language MATLAB.

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Lagrange function minimize

Suppose f(x) is a function we want to choose x so as to minimize f(x)=Ax-b under constraints x>=0. A is a Matrix (n*m) not symmetric and x and y are a vectors. I do f(x)=A'Ax-A'*b and then I want to ...
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Crank nicolson method to solve couple nonlinear pde [on hold]

how to solve couple nonlinear pde using crank nicolson method...I need a matlab code for this..plz help me.
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Matlab PDE toolbox problems specifying geometry with large size differences [on hold]

My problem comes up in an attempt to calculate dislocation bias factors in bcc Fe. I am following a paper by Chang et al found at Science Direct. To do this, I am trying to solve an elliptic PDE ...
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Solving Time dependent Schrodinger equation using MATLAB ode45

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 ...
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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 ...
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Approximating improper integral with FFT

In d'Halluin et al. (2005) (http://imajna.oxfordjournals.org/content/25/1/87.short) the authors claim that the correlation integral $$I(x) = \int_{-\infty}^{\infty} V(x+y) f(y) dy$$ can be ...
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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 ...
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Conservative Short Sales Portfolio Optimization with MatLab code help

I'm trying to solve the optimization problem below with MatLab, but I'm unsure of how to modify the constraints in the quadprog function (or how to add the constraints with the Portfolio object). In ...
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Conjugate symmetry in MATLAB?

I have a large vector with complex numbers. How do I check whether it a conjugate symmetry vector? If not, is there any way to transform it?
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Discretized matrix from the integral kernel function

Recently, I read a paper [1] and then I want to handle the two-dimensional linear integro-differential equation \begin{equation*} -\triangle u + q\Big(\frac{\partial u}{\partial x} + \frac{\partial u}{...
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Stiffness emerges as number of ODEs increases

I want to solve a system of ordinary differential equations with Matlab. I need this to solve a mechanical engineering related problem. If $n$ is the number of degrees of freedom of my mechanical ...
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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. ...
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Difference between Brent's and Alefeld-Potra-Shi for root finding

I need to find the (unique) root of a nonlinear function $f(x)$, $x \in \mathbb{R}$. For the record, $f(x)$ is the CDF of a probability density minus a constant $0 < p < 1$ (I am inverting the ...
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Solving system of constrained linear and non-linear equations in MATLAB

Solving system of constrained linear and non-linear equations in MATLAB I'm solving a FEM problem in MATLAB with use of the direct stiffness method. The problem is now formulated as a system of nn ...
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How to write a function that its plot is like a “M” in MATLAB

I wrote a code in MATLAB that solves parabolic equation of two space (heat equation:$u_t = u_{xx} + u_{yy}$ )with ADI (Alternating direction implicit) method (finite difference method). Now in order ...
82 views

Integer programming with Matlab

I'd like to know how to solve in MATLAB the following integer optimization problem : $\underset{B,D}{\arg\min} \Vert{Y-XDB}\Vert_{2}$ where $X,Y$ are given matrices. The constraint is the following ...
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Stability of matrix equations in MATLAB

Is there a method to check for unconditional stability or positive-definiteness of large matrices in MATLAB? For example, I know that matrices with property M (positive main diagonal elements and ...
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Preconditioned Conjugate Gradient linear system solver in MATLAB

I have been trying to use the MATLAB's pcg() function to minimize an energy functional. Converting minimization problems to the solution of a linear system is ...
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Solving linear systems with ill-conditioned matrices

As per suggestions of the people from MathOverflow, I'm reposting my question here: I'm currently trying to solve a linear system $Ax = B$, where the matrix $A$ is ill conditioned (i.e. nearly ...
153 views

Introduction to Lattice Boltzmann methods [closed]

I am trying to learn the Lattice-Boltzmann method and was looking for some good beginner resources explaining the method. I have been looking at some codes online, but have been having trouble ...
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How to create node to node lumping

I have been doing finite element analysis using Matlab. I look for many examples and tutorials producing only the stiffness matrix letting elements being weightless. However, in my case i need to do a ...
99 views

How to solve a constrained optimization problem using minFunc or minConf

I am trying to solve the following optimization problem: \begin{align} &\min\limits_{s} \rm{tr}\left(S^T S\right) + \mathrm{tr}\left(\left(S^T S\right)^{-2}\right)\\ &\text{subject to }\rm\...
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Calculate the intersection of two matrix kernels in MATLAB

If we have a discrete saddle point problem with the coefficient matrix $$\mathcal{A} = \begin{bmatrix} A & B^T \\ B & 0 \end{bmatrix},$$ then $\mathcal{A}$ is invertible, supposing \$...
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How can I generate 3D unstructured mesh on MATLAB

I have been looking to do a 3D mesh for a shallow tunnel FE analysis. The output of mesh node orientation along the element should be counter clock wise direction. How and which material helps me best ...
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How to apply asymptotic matching condition in bvp4c?

I want to know how to write the code to apply asymptotic matching condition? In the paper, it is stated that they apply asymptotic matching condition for the range of ...