Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

Filter by
Sorted by
Tagged with
0
votes
1answer
249 views

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. ...
2
votes
1answer
180 views

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 ...
1
vote
0answers
356 views

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 ...
-3
votes
2answers
121 views

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 ...
0
votes
1answer
175 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 ...
-1
votes
2answers
439 views

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 ...
8
votes
0answers
166 views

Tucker factorisation to compare multiple PCA decompositions?

This is an entry-level question for multiway matrix decompositions. I have a set/population $k$ of entities (here biological cells) for each of which I also have a number ($l$) of flavours of length $...
0
votes
1answer
1k views

COMSOL: get list of eigenfrequencies [closed]

In COMSOL, is there a way to get it to export a txt file with all the eigenfrequencies found during an eigenfrequency analysis? I suppose that it could be done through the MATLAB interface or through ...
1
vote
1answer
1k views

How to solve the problem without using symbolic computation

I have the following simple nonlinear equations with two unknowns only: $$\left\{ \begin{array}{c} \int_1^2{\dfrac{ e^{{a_1} x+{a_2} x^3}}{1+x^2}} \, dx=1 \\[13pt] \int_1^2{ x^2 e^{{a_1} x+{a_2} x^...
1
vote
2answers
1k views

Difference between Data structure objects and cell array objects in matlab

I want to know what are the differences between two data structures in MATLAB: Structure Arrays and Cell Array. In what circumstances we can use each of them?
1
vote
0answers
80 views

Need help writing the code for the following optimization

I need to find $X$ for which the following expression is minimized: $$ \min ||Y - F^{-1}(X)||_2 + ||X||_1 $$ where $Y$ is an array (of length approx 44000, an audio sample I will be reading using ...
4
votes
0answers
188 views

Galerkin FEM error when using even number of elements

Intro: I am developing a Galerkin FEM code in matlab - starting small with a simple 1D ODE. The equation I'm trying to solve is: $$a u_x = cos(x), x \in [0, 2\pi]$$ Which has a known exact solution $$...
2
votes
1answer
867 views

Numerically computing the advection equation

I am trying to write a program to compute the advection equation. $$u_t +u_x = 0$$ I use the spectral method for the spatial derivative $u_x$ and the leapfrog method for the time derivative $u_t$. ...
1
vote
1answer
72 views

Handling figures built for different parameters in Matlab

I couldn't find a simple answer to this thing I'm trying to do in Matlab. I have a function file that does some calculation for a given parameter a: ...
1
vote
0answers
151 views

Scaling a vector-valued non-linear function for numerical optimization/minimization [closed]

I am trying to minimize a non-linear vector-valued function in MATLAB. As a test case for my code, I try to minimize a function whose solution I know apriori. The problem is that one of the ...
1
vote
2answers
58 views

MATLABs double arithmetic

this is a classical problem, but I need help to pinpoint what I am missing. Problem: In MATLAB (exp(1) + 10^12) - 10^12 gives you a double which equal to e, up to 5 correct digits. But I thought ...
2
votes
2answers
2k views

Code for shallow water equation

I want to write a MATLAB code for Roe solver for 1D shallow water equations. Is there anyone who can help me with that?
1
vote
1answer
446 views

Matlab integral with vectorized bounds, without using a loop

I have a simple question that I wasn't able to find an answer to. I have a function f(x) where x is some vector, for example: <...
2
votes
1answer
77 views

Is more robust to digit cancellation the sum operator or the mean operator?

Note: this question is not strictly related to Matlab or any other environment (even though I would prefer that you refer to my Matlab code). I've n = 10000 ...
0
votes
1answer
505 views

How to solve my PDE's in Matlab?

I need to solve a set of 5 PDEs for functions $u(x,t)$. I looked up the Matlab function pdepe. It looked perfect for my case, until I read the line: $f(x,t,u,\...
2
votes
1answer
2k views

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 ...
2
votes
1answer
3k 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 ...
0
votes
1answer
297 views

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 ...
1
vote
2answers
367 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\...
1
vote
1answer
199 views

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 $...
3
votes
3answers
525 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{...
1
vote
3answers
2k views

Numerical simulation of a reaction-diffusion system on MATLAB with finite difference discretization of spatial derivative

I have a model of a system which consists of diffusing reactants and intermediates. For each variable, $u_i$, the final representative equation looks like the standard reaction-diffusion form: $$\...
0
votes
1answer
207 views

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 ...
1
vote
0answers
37 views

How to find active region in treepartition Matlab object

I am trying to identify a non-linear plant using the identification toolbox of Matlab. In particular I would like to identify a non-linear arx model, where the nonlinearities are expressed by means of ...
1
vote
0answers
611 views

3D plot from Fourier coefficients in Matlab

I would like to construct a surface on a 2D mesh, given a set of Fourier coefficients for the original function $V(x,y)$. Given some $\mathbb{K}\subset \mathbb{Z}^2$ I have a partial double sum of a ...
1
vote
1answer
290 views

I need to deconvolve the image of a fluorescent bead without the Point Spread Function in MATLAB

I am aware that I could use deconvolution algorithms such as LUCY, Weiner and Blind but I am confused as to how to estimate the PSF (point spread function), which is needed for the LUCY and Weiner ...
1
vote
1answer
2k views

Solving second order SDE with Gaussian white noise for first time derivative in Matlab

I'm having trouble solving a second order differential equation with Gaussian white noise. The equation I'm solving follows the form: $$Ax'' + Bx' + \sin(x) = i + i_{n}$$ where $i_{n}$ is the ...
0
votes
0answers
324 views

3D Diffusion Equation in Fourier space

I'm solving the 3D Diffusion equation $$u_t=k(u_{xx}+u_{yy}+u_{zz})$$ in MATLAB using Fourier techniques. I assume a 3D Fourier expansion $(e^{-ipx},e^{-imy},e^{-imz})$of the solution. Physical ...
3
votes
1answer
1k views

How can I minimize the number of non-zero elements in the solution vector subject to linear constraints (MATLAB)?

all, I've tried to find an answer to this question and have come across some related threads but nothing I was able to apply to my problem given my relative lack of experience in this arena. I ...
1
vote
0answers
242 views

Extracting sinograms from tomography projections

my name is Lorenzo and I am a postdoc researcher in Italy. My job is related to tomography imaging using synchrotron radiation. This is a new field for me and I start to face with Matlab to write some ...
7
votes
3answers
2k views

How to compute the rank of a large sparse matrix in MATLAB

I am interested in computing the ranks of fairly large, the largest being of magnitude $10^6$ x $10^6$, sparse matrices whose entires are all 0, 1, or -1. I have been trying to use Matlab to ...
1
vote
1answer
573 views

Shooting method - Matlab ODE

I'm trying to solve these equations of hypersonic adiabatic flow over a flat plate. I did all the simplifications and got these equations for the stagnation point flow. $$\left(Cf''\right)' + f f'' = \...
3
votes
1answer
1k views

Solving system of 7 nonlinear algebraic equations symbolically

I have a system of seven nonlinear equations that I want to find their symbolic solutions. The solution will depend on the parameter K, and I should have different solutions by varying the parameter. ...
-3
votes
1answer
208 views

How can I solve stiff equations by method of line (MOL)?

I want to solve 7 coupled equations.I use method of line(MOL) and discrete the equation in Length and radius and convert them to a system of ODEs in time.and use ode15s to solve them in MATLAB. But an ...
1
vote
3answers
258 views

solving PDEs in MATLAB

I want to solve 3 coupled equations. I converted them to a system of odes in time and discrete it in Length and radius. Now I have a problem in one of the equations in first point. Because in this ...
3
votes
2answers
373 views

Known issues with eigenvalue numerics?

Are there any known issues (such as precision issues) with $\mathsf{MATLAB}$ eig and charpoly functions for large enough $\{-1,0,+1\}$ matrices? Even if I change $1$ or $2$ entries between matrices ...
2
votes
1answer
553 views

Is the "practical" complexity of linsolve direct solver O(n^2) ?

I recently timed the linsolve direct solver and I was kind of shocked to see that the solver seemed to be scaling quadratically even upto a 1000 dimensions. Specifically I ran the following code and ...
0
votes
1answer
169 views

maltab ode solver- user defined criteria to stop calculations

is there a way to add a user defined convergence criteria to an ode solver so that the solution is stopped? I know that Matlab uses absolute and relative tolerances but would that suffice in solving ...
0
votes
3answers
957 views

How to plot a price level matrix in Matlab?

I have a matrix P of m rows and n columns. P(i,j) contains the price of occupying position i at time j. I want to plot this in Matlab but in a way to get some kind of density plot with different price ...
1
vote
0answers
108 views

How to get mathematical model from a data set with MATLAB

I have some values imported from excel about the annual sell of a product, with 3 var: month, price, sold items I have seen how to plot a chart using curve fitting tool but I need to define a ...
2
votes
1answer
1k views

Numerical method for a BVP with mixed boundary conditions (MATLAB)

I've been given a second-order non-linear ODE: $$\frac{d^{2}\theta(s)}{ds^{2}} = sf_{g}\cos{\theta} + sf_{x}\cos{\phi}\sin{\theta}$$ where $f_{g}, f_{x}$ and $\phi$ are constants. The boundary ...
0
votes
2answers
5k views

Plot vector field in matlab

I have the function of an electric dipole expressed in cartesian coordinates and I want to create the vector field using Matlab . The function is $$E_z= \frac{p}{4\pi\epsilon_0} \cdot \left(\...
2
votes
0answers
184 views

Modeling First Order Parabolic PDE (Battery Storage Model)

I'm trying to solve the following first order parabolic partial differential equation, \begin{equation*} X \frac{\partial V}{ \partial Q} = -\frac{1}{2} \sigma^2 \frac{\partial^2 V}{\partial X^2} + ...
0
votes
1answer
135 views

Calculation of error

I have written a code in which I find the approximation of the solution of this elliptic problem. I calculated the error using the following part of code: http://pastebin.com/7b5mmuRW but I get the ...
1
vote
1answer
97 views

Integrating a function and then plotting it's graph in Matlab

I've been working on this code for some hours and it seems I'm doing something wrong which I just can't figure out. I have a function which I integrate and then plot it's values. But the graph I get ...

1
6 7
8
9 10
16