Questions tagged [matlab]

Questions about the numerical programming language MATLAB.

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103 views

Continuation of solution to $-\nabla\cdot (k(x,y)\nabla u)=f$

I'm trying to solve the following problem, I had previously opened another discussion for the implementation and well, it seems that it has turned out well, it can be found here. I need to calculate ...
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0answers
23 views

TIMESAT Error: Wrong number of sensordata imagefiles in Fortran command window [closed]

I am a first-time user of TIMESAT, and am attempting to follow along with this tutorial. http://rstudio-pubs-static.s3.amazonaws.com/452032_a5df2d3f782444fc830d43548a304ec5.html#PartA However, I am ...
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0answers
26 views

Is there any way to develop MultiStart method in c++? [closed]

I have to convert some Matlab code into C++ code. These functions are used in this code. createOptimProblem(....) MultiStart(....) run() I have only basic ...
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2answers
219 views

Implementing routine for $-\nabla\cdot (k(x,y) \nabla u)=f$ in Matlab

I am solving the Poisson Equation for 2D given by the following expression: $$-\nabla\cdot (k(x,y) \nabla u)=f$$ in a rectangle with Dirichlet conditions on the boundary using Matlab. In principle I ...
2
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1answer
78 views

Vectorization Matlab/Octave of Markov Matrix Powers

I have just created a code snippet in Octave/Matlab that aims to create a plot which shows the accuracy of an initial probability vector $\vec{\pi}$ derived from the transition probability matrix $\...
3
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1answer
79 views

How can I extract the banded or block diagonal part of a sparse matrix in MATLAB?

Given a large sparse (square) matrix in MATLAB, how can I extract the banded or the block-diagonal parts (of fixed size) of it efficiently? These are useful operations when prototyping and testing ...
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1answer
116 views

Interpreting multivariable root-finding results from Matlab's fsolve algorithm

Edit: So I was able to get the same value of r that's given, when coding up the sum of squares of function values directly in the script file, rather than on the Command Window. So, maybe there's a ...
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1answer
88 views

What is the use of arrayfun if a for loop is faster?

This may not be so much of a scientific computing question but more of a MATLAB question, if that is the case, please feel free to close or migrate the question. Root-finding problems are commonly ...
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1answer
40 views

Efficient solution to linear system involving Kronecker sum in MATLAB

High dimensional finite difference problems often lead to linear systems of the form $$ A x = b, \qquad A = B_1 \oplus B_2 \oplus \cdots \oplus B_d, $$ where $\oplus$ denotes the Kronecker sum. $B_i \...
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3answers
238 views

Converting from planar polynomial domain to planar polygon

Let's assume we have a planar domain whose boundary can be described with a polynomial curve (like Bezier curves). Now assume that you want to produce a discretization of the boundary, i.e. you want ...
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2answers
538 views

Specifying ode solver options to speed up compute time

I'm specifying the 'JPattern', sparsity_pattern in the ode options to speed up the compute time of my actual system. I am sharing a sample code below to show how I ...
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0answers
46 views

How to solve semidefinite program using CVX?

I am reading the research paper Abel Molina, Thomas Vidick, John Watrous, Optimal counterfeiting attacks and generalizations for Wiesner's quantum money, 2012. and I want to prove the SDP result in ...
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40 views

Path constraints for state variables - fmincon, ODE45

My problem lies in constraining state variables (look for 23,24,25). I am currently using ODE45 to solve equations and fmincon to find best control variable.How would you go about solving this? Here ...
4
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1answer
93 views

How are Matrices Stored in MATLAB?

I have this simple question but I am trying to figure out why: Are matrices stored column-wise in MATLAB? If so then why? I theorize that they are stored column-wise because the memory does not have ...
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0answers
51 views

Can I get a symbolic solution for these coupled ODEs?

I found this IPython notebook called ‘Roller Coaster’ from", "numfys.net, where they model the movement of a ball over a path described by a third-degree polynomial $y(x)$ with slope $\...
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1answer
140 views

MATLAB : find an algorithm to inverse quickly a large matrix of symbolic variables

I have to solve the equality between 2 matrixes 12x12 containing a lot of symbolic variables and with which I perform inversion of matrix. There is only one unknown called "...
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1answer
43 views

Round-off error step choice

In the Numerical Recipes in section 5.7.- Numerical derivatives the choice of the step size $h$ in the numerical derivative should lead to a difference between $x$ and $x+h$ representable by an exact ...
1
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1answer
137 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 ...
1
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1answer
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 ...
2
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1answer
257 views

Minimal surface finite differences problem - Matlab assemble

I face to the following problem: $$(1+u_x^2)u_{yy} - 2u_xu_yu_{xy} + (1+u_y^2)u_{xx}=0.$$ Problem needs to be discretized and assembled. Does anybody know how to proceed in Matlab?
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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 ...
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0answers
36 views

Using event function to shift between 2 sets of ODE

I have a bunch of ODEs I am trying to solve using ode45 in MATLAB. I have hidden the details of the equations to keep it simple (so as to build a general algorithm)! \[\frac{dR}{dt}= F_{1}(R,N) \quad\...
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0answers
29 views

Problem with Numerical DAE Implementation of Nernst-Planck Equations

I write to you all today in order to clarify if I implemented my model correctly into MATLAB. I will outline the following: analytical governing equations, my discretization for the equations and ...
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2answers
779 views

Complex Eigenvalues using eig (Matlab)

I wanted to find and plot the eigenvalues of large matrices (around1000x1000). But discovered when using the eig function in matlab, it gives complex eigenvalues when it shouldn't. For example, in the ...
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2answers
166 views

How can I learn Scientific Python?

I am an intermediate user of Matlab and Mathematica, but I would really love to start learning Python language for scientific purposes (I am interested in Maths and Physics). Could please someone ...
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0answers
79 views

Error $L_{2}$ convergence in Finite Element for Poisson Equation

I have written a Matlab code to solve the equation $-u'' = f$ with conditions $u(0) = u'(1) = 0$ on the domain $x \in [0,1]$. I tested the code with $f(x) = -2, \forall x\in [0,1]$. I check the plot ...
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1answer
37 views

Rem function in Octave showing wrong result

I am trying to write an if statement that checks if 2 numbers are divisible before running some commands. The problem is, the rem function is giving some wrong results for certain number (2 is ...
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1answer
74 views

Reason behind different outputs for Fast Fourier Transform in Numpy and Matlab

Here is the output of Numpy np.fft.ifft([0, 4, 0, 0]) array([ 1.+0.j, 0.+1.j, -1.+0.j, 0.-1.j]) # may vary Here is the output of Matlab ...
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1answer
47 views

How to reduce computational time in DDE simulation on Matlab

I need to simulate a network of nodes. The weights of the edges are being given in a matrix . Due to the non-zero distances between the nodes, we consider time-delays, which are computed given the ...
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0answers
79 views

Advection equation boundary conditions in 2D unstructured grid

Currently struggling with boundary conditions for 2d advection equation. left dirichlet u = (1,0) bot top dirichlet u = (0,0) right neumann du/dx = (0,0) ...
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1answer
70 views

ODE45 and a variable that assumes multiple values during the timespan

I have tried in different ways to see what happens to voltage V and gating conductances m, n and h when, at time step x, current I switched from 0 to 0.1, and then at time step x + n it gets back to 0....
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2answers
3k views

FEM Stiffness Matrix is always close to Singular or Badly Scaled

I am making a code for an 18-node (3x3x2) 3D element FEM. However, even though I am (pretty) sure that all the shape functions are correct and whatnot, whenever I try and invert the stiffness matrix ...
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1answer
23 views

Software to find zero divisors of a ring

Are there some programs with packages that help to list all zero-divisors of the ring we desired? especially for the ring of Gaussian integers modulo $n$, $\mathbb{z}_n[i]$. Also want to find which of ...
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1answer
126 views

Plotting the difference between an exponential and its Taylor expansion as a function of number of terms?

I'm terribly green, please forgive me. I need to plot the difference between a chosen calculated Taylor expansion $e^x=1+x+\frac {x^2}{2!}+\frac {x^3}{3!}+\frac {x^4}{4!}+\frac {x^5}{5!}$... and the ...
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2answers
1k views

Solving DAE with higher index

I want to solve 7 coupled differential equations in MATLAB. I used the method of lines (MOL) to convert them to a system of DAEs. I then attempted to solve this system using ode15s. Unfortunately an ...
3
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4answers
302 views

How does gmres method iteration behave for this non-diagonalizable matrix?

Recently, I have been studied my lessons about gmres iteration, probably the most popular iteration method for general large sparse linear system of equations Ax=b. And the convergence is obtained ...
8
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1answer
9k views

Matlab solution for implicit finite difference heat equation with kinetic reactions

I am trying to model heat conduction within a wood cylinder using implicit finite difference methods. The general heat equation that I'm using for cylindrical and spherical shapes is: Where p is the ...
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1answer
79 views

Visualize a mesh from list of 3D point and faces

I have a list of vertices and faces. Now, I want to create a mesh using the given points and faces list and visualize it. Also, I want to play with the mesh by adding an extra point on the faces. Can ...
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0answers
74 views

C.S.R method in finite element matrix assembly

I have solved the 2D Poisson equation using finite element method with simplex triangular element in MATLAB. First, I generated the triangular mesh using pdetool in ...
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1answer
40 views

Solving differential equation by setting vectorization `on` in MATLAB

This is a follow up to my previous question posted here. I've set up an ode system in MATLAB and I'm trying to vectorize the code to increase the speed of computation. The follow is the code for my ...
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2answers
350 views

How to set up the differential equation system to speed up computation?

I've set up a system of differential equations, obtained after discretizing pde, in the following way ...
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1answer
68 views

Solving differential equation by specifying jacobian pattern

This is a follow up to my previous question posted here I'm trying to construct the sparsity pattern of the jacobian matrix to speed up the computation of a large system of odes. The following is the ...
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1answer
48 views

solving differential equations with jacobian pattern

I'm trying to compare the simulation time for solving a system of differential equations with and without jacobian pattern for a toy model using ode15s in MATLAB. ...
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0answers
42 views

How to solve this boundary value problem which has more unknown than equation on MATLAB

I need your helps about solving the problem below with MATLAB. I am trying to solve 2D Stress Wave Propagation problem by using FDTD(Finite difference time domain) method on the cylindrical coord. I ...
3
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1answer
95 views

Anomaly in 2-body simulation error

I've generated a solution for a planet motion around the Sun (placed at the reference frame center). I wanted to test what would I get for the error of the method I'm using (Runge Kutta with 4 stages, ...
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0answers
19 views

Improve code of logarithmic quantizer

I am implementing a logarithmic quantizer which is defined as follows: $$ q(u) = \begin{cases} u_i , \frac{u_i}{1+\delta} < u < \frac{u_i}{1-\delta} \\ 0 , 0 \leq u \leq \frac{u_o}{1+\delta} \\ -...
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0answers
37 views

Calling User defined Matlab Functions in Python with Matlab.engine API

I am trying to combine Matlab and python scripts and figure out if I can achieve a better solution in terms of the solver-runtime. A very simple optimization problem is used just for now. But I got in ...
0
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1answer
61 views

How to solve a Stiffness matrix?

I am quite new in this field. For my university I prepared a stiffness matrix to solve for a project group. This matrix consists of 450 equations with 450 unknows (it's a Matlab script) and I have the ...
0
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1answer
106 views

Verification of order of convergence of Implicit Euler Method to numerically solve Black-Scholes PDE

I'm trying to verify the order of convergence for implicit Euler method to numerically solve Black-Scholes PDE. Theory says that it should be $O(\Delta t + \Delta S^2).$ My code is working absolutely ...

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