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1answer
565 views

Pde problem with robin boundary condition

I have my pde 2D problem with robin condition (form: du/dn +ku=g) to solve with matlab. i have the exact function u and I want to find the function g in robin condition. How can i do it? thanks for ...
-1
votes
3answers
169 views

Solving coupled ODEs using Runge-Kutta method

I want to solve the following sets of $n$ coupled equations. Initial values of $x_{n}(t)$ and $p_{n}(t)$ are specified. The problem is, I have an 1D lattice where every particle is bound with ...
-1
votes
1answer
77 views

Is it possible to simulate life? [closed]

Has anybody ever managed to simulate even the simplest form of life by merely simulating the interactions of the molecules of the organisms body? What would be the theoretical minimum number of ...
-1
votes
1answer
2k views

Using scipy.odeint to solve coupled equations [closed]

I have a set of three coupled autonomous equations: ${y_{1}}\prime = y_{1}(\frac{\Omega_{m}}{y_{1}^3} + \frac{y_{3}^2}{6.0} + \frac{V(y_{2})}{2.H_{0}^2})$ $y_{2}\prime = y_{3}$ $y_{3}\prime = -3\frac{...
-1
votes
2answers
394 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 ...
-1
votes
1answer
53 views

Plot of a function involving an integral and value changing parameters [closed]

I'm trying to plot the cross section with respect to the photon energy $h\nu$ but for $\gamma = 1.0, 1.2, 2.0 $ in the same axes $\sigma = \left[\left(\frac{\xi_{eff}}{\xi_{0}}\right)^2 \frac{n_r}{\...
-1
votes
1answer
46 views

Detecting degenerate triangles with very thin structures

Between the two ears in the following bunny images, there are some degenerate triangles I want to detect. It looks like a volume-less thin slits. If the question is not clear, please let me know.
-1
votes
1answer
37 views

Numpys `tensordot` and what is happening mathematically

I've encountered a program where np.tensordot was used, so I tried looking it up but I can't really understand what this function is doing... I feel rather ...
-1
votes
1answer
97 views

How to implement the Hessenberg QR Algorithm?

For context, I'm creating a linear algebra library from scratch for learning purposes in C. Right now I'm working on calculating eigenvalues but my implementation of the QR Algorithm is diverging. ...
-1
votes
1answer
100 views

Simulating 1D diffusion

I'm trying to understand the influence of Neumann boundary condition while simulating 1D diffusion equation $$ \frac{\partial C}{\partial t} = \nabla \cdot (D \nabla C). $$ The initial value is set ...
-1
votes
2answers
120 views

How to use natural logarithm inside Expression on FENICS

I'm trying to evaluate the exact solution of heat diffusion in circular plate. I'm not able to use the natural logarithm inside expression. ...
-1
votes
1answer
358 views

Which ODE solver in Matlab allows me to advance in just one timestep only

[t,y] = odeXX(odefun,tspan,y0) I have a solver odeXX, and the tspan = [0 0.0001]. It seems that for any ode solver in MATLAB, they integrate by breaking ...
-1
votes
1answer
394 views

Finite Difference for Fourth-Order PDE

How to discretize the following 4th order PDE using finite difference method? $$\frac{\partial^{2} y}{\partial t^{2}}+\frac{\partial^{4} y}{\partial x^{4}}=0$$ thanks
-1
votes
1answer
59 views

Is it possible to find a formula for a set of number from the result? [closed]

I have these two sets of number, I also have a result. Is it possible to compute the relation between them so that I can figure out how the result is generated ? for example I have : Set A=4 6 12 25 ...
-1
votes
3answers
159 views

How to solve numerically such system of equations

I have a system of equations $$ S_{m}(\xi) +P_{m}(\xi)=f(\xi) $$ where $\xi$ can be choosen arbitrary in some domain in $\mathbb{C}$, $f$ is known, $P_m$ is a polynomial of degree at most $m$. ...
-1
votes
1answer
22 views

How to connect two cylinders to form a knee in Comsol Multiphysics?

I have this I want it to be single bended wire. How to accomplish?
-1
votes
1answer
95 views

Numerical solution for gradient(slope)

Abstract I have the next equation to find a force, for my problem: $$U=-\int \vec{m}\small{(x)}\times \vec{B}(x)dV$$ $$\vec{F}=-\nabla U$$ Considering 3-dimensional space with x,y,z coordinates, ...
-1
votes
1answer
38 views

Why does this line of code give a flat distribution?

I'm struggling to understand a line of FORTRAN code and was hoping someone on here would be able to help me out. These lines of code are meant to generate a flat distribution - I understand that GRNDM(...
-1
votes
1answer
73 views

Solving a large system of coupled ode. (Python)

I really have a problem here. I have not found a solution yet. The system I need to solve similar to this:(Basic idea) $$c_1 = \dfrac{dx}{dr}+y$$ $$c_2 = \dfrac{dy}{dr}+x$$ Both $c_1/ c_2$ are ...
-1
votes
1answer
90 views

If not MATLAB, what software/programming language should I use to simulate/animate wave functions in various potentials + more? (example given)

I want to integrate programming into my learning in math and science in a very specific way. I want to create visualizations and simulations of concepts I am learning. When I learn a numerical method ...
-1
votes
1answer
42 views

Matrix requirements for cusparse*csrgemm2

I would like to perform a matrix multiplication like: $C=A*B*A'$ using cusparse library function cusparseDcsrgemm2. To do this I split it into two matrix-matrix multiplications where all matrices ...
-1
votes
1answer
16 views

How to Collect fraction in Maple 18? [closed]

Suppose I have $$f=\frac x 3+ \frac y 3 +\frac z 3$$ And I want to use collect(f, 1/3) And I wish it will displays $$f=\frac1 3(x+y+z)$$ But it doesn't work....
-1
votes
1answer
1k views

Scipy Two-point Boundary value Problem

Nonlinear ODE Statement I would like to use scipy to solve the following: u'' + (u')^2 = sin(x) u(0)=0, u(1)=1 where u = u(x). Approach I am looking at the ...
-1
votes
1answer
74 views

Relation of Condition of a Matrix and Convergency

Can anybody explain me the relation between the condition of a Matrix and the convergency of a problem. For example how is the relation between the condition of the stiffness Matrix occuring in FEM ...
-1
votes
1answer
73 views

Anyone knows where I can find a simple FEniCS code where I can understand basic implantation? [closed]

I found this one, but does not work: http://www.karlin.mff.cuni.cz/~hron/warsaw_2014/pl2014_lecture5.pdf
-1
votes
1answer
576 views

Stability analysis for coupled nonlinear system of partial differential equations

I'm trying to solve a nonlinear partial differential equation \begin{equation} L(u_{xxtt},u_{xx}u_{tt},u_{xt}^2,u_{xt},u_{tt})=0 \end{equation} using finite difference methods. In order to remove the ...
-1
votes
1answer
63 views

I have a problem in finding the exact area and estimating the error [closed]

The program should first read from the keyboard the values of a and b then estimate the area under f(x) in the interval [a, b] using Simpson’s 1/3rd rule and display the estimated area and the error ...
-1
votes
1answer
150 views

Problem using MATLAB `fminunc` [closed]

I am trying to find the minimum of this function. But I receive the following error when I run the script. What am I doing wrong: ...
-1
votes
1answer
383 views

How to initiate spirals in this model?

I am trying to reproduce Tang & Othmer paper which is related to excitations and oscillations in G-protein model in Dictyostelium discoideum, an amoeba species. The mathematical model in the paper ...
-1
votes
1answer
84 views

Is iteration an efficient algorithm in this case? [closed]

My task in numerical analysis is We are interested in finding values of β0 for which z(x) = 2500. Use an efficient algorithm to determine the rays which pass through the receiver. Now I'm just ...
-1
votes
1answer
213 views

Solving large system of equations, is linear programming best option? [closed]

I have a problem where I am trying to solve many systems of equations, that have very few variables per equation, but a lot of equations. For example potentially 10 variables max in a single equation,...
-1
votes
1answer
182 views

How do I stop negative numbers and error message: " Failure at t=3.562559e+03. Unable to meet integration tolerances

I am using 8 ODEs in Matlab to simulate the effect of asymptomatic infections in the epidemiology of a vector borne disease. Searching the parameter space under certain settings produces negative ...
-1
votes
1answer
123 views

Can you give some information for rothe method [closed]

I want to learn a numerical method for PDEs other than finite difference method. After some research on internet i have found Rothe method and it looks interesting to me. Unfortunately, i couldn't ...
-1
votes
1answer
102 views

Libraries with the method of lines for parabolic PDEs [closed]

Could you please advise some programs or libraries for solving parabolic PDEs (or its systems) in 1D, 2D and 3D, for example, with the method of lines? The system of parabolic PDEs can be nonlinear in ...
-1
votes
1answer
5k views

Runge-Kutta 4th order for 4 coupled first order differential equation [closed]

I have to solve 4 coupled first order differential equations for $f(t)$ ,$g(t)$, $h(t)$ and $w(t)$ witch are only functions of $t$ , but for every reference link a function of 3 variables is assumed (...
-1
votes
1answer
1k views

Explicit scheme for heat equation with Neumann boundary conditions in Maple

$\displaystyle \frac{\partial u}{\partial t}=\alpha(x,t)\cdot \frac{\partial^2 u}{\partial x^2}+b(x,t)$ $u(x,0)=f(x)$ Initial condition $u_x(0,t)=0$ 2nd type Boundary condition $u_x(1,t)=0$ 2nd ...
-1
votes
1answer
230 views

A question on CHOLMOD: long int vs int, still failing after change to long int [closed]

Changing cholmod_* to cholmod_l_* results in the following error: sparse:error: integer and real must match the routines ...
-1
votes
1answer
765 views

Open Foam User Guide Tutorial [closed]

I am trying to follow the Openfoam user guide but I'm stuck at the first tutorial 1. In fact, when I try to run the blockMesh command (using the administrator account), the following appears: ...
-1
votes
0answers
25 views

Are superluminal computers possible? [closed]

I have no idea how a computer works on the lowest voltage moving through tiny circuit chips level, but if you wanna travel space from one star to another, don't you need a faster than light ...
-1
votes
0answers
28 views

How to derive the corrector step for the eq $\frac{\partial u}{\partial t}+\frac{\partial f}{\partial x}=0$

Let define a predictor step for the equation $\frac{\partial u}{\partial t}+\frac{\partial f}{\partial x}=0$, by: $$U_{i+\beta}^{n+\alpha} \equiv \bar{U}_{i}=U_{i}^{n}+\beta\left(U_{i+1}^{n}-U_{i}^{n}\...
-1
votes
0answers
16 views

Problem with physical groups to label surface in GMSH

I'm having some troubles setting the ID for the physical group of the boundary and then extract them later in Python. Here's my main.geo file: ...
-1
votes
0answers
20 views

Constrained optimization with CVXPY package in python

I have a following convex optimization problem with a KL-divergence constraint. I am wondering can I solve it efficiently using CVXPY package? If so, could you please help me some detailed codes? I do ...
-1
votes
0answers
47 views

Analytical vs Numerical solution to differential equation with final value

I have the following differential equaiotn: $x' = -x-2$ with a final value x(2)=0. I solved it analytically and got: $x(t)=2(e^{2-t} -1)$. It satisfies the final condition x(2)=0. Also, at t=0, x(0)=...
-1
votes
1answer
25 views

An almost surly fine-time game of coin toss where you win with probability $p$

Given a fair coin and a number $p\in(0,1)$. How do you design a game that finishes in a finite number of tosses with a probability of $1$? And further, with the probability $p$ you win the game. I ...
-1
votes
1answer
47 views

Find mass matrix in a system of linear equations

Given $z_t=\sum_{i=1}^t \theta_iz_{t-i}+v_t $, where $t=1,...,N$ where $N=1024$. I need to write this in matrix form (a system of linear equations) as $\mathsf{A}\mathsf{z} = \mathsf{z} - \mathsf{v}$. ...
-1
votes
1answer
19 views

surface: rows (Z) must be the same as length (Y) and columns (Z) must be the same as length (X) in octave

I am having a dataset and trying to plot a 3-d plot between the independent and dependent variables.but, I am getting this error whenever I am trying to plot here is my code: ...
-1
votes
1answer
57 views

How to solve system of equations with almost-zero determinant?

I have a system of equations that I am trying to solve. In matrix form, it's written as $$x(I - S) = b.$$ I am solving for $x$, where $I$ is the identity matrix and $S$ is a matrix where each column ...
-1
votes
1answer
49 views

How to get free energy surface of a 3d Ising Spin system using Monte Carlo simulation?

I am doing a Monte Carlo Simulation of the properties of a 3D Ising Spin system. I want to get the free energy surface of the spin system from the simulation. It is a magnetization vs free energy ...
-1
votes
1answer
88 views

Finding derivative of Matrix at different grid points using Finite difference methods/ Cholesky Factorization

I want to code this problem in MATLAB. It would be a huge help if someone can suggest to me how I can approach it. I need to solve the below-highlighted equation, I need ...
-1
votes
1answer
35 views

FORM by NIKHEF: unexpected behavior wrt summation

I have two almost identical FORM (by NIKHEF) scripts here: script_1 script_2 which differ only in summation at the end. In first case the summation in done in one step, in the second case ...

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