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Computational Science : Recent Questions and Answers (Page 10)

Find answers to your questions about Computational Science or help others by answering their Computational Science questions.

Uniaxial stretching solution not uniform in FEM code

I am trapped here for a long time. I wrote a toy Matlab FEM code. I want to run the follow simulation.MeshSuppose we have a cube, and we divide it...

Asked on 08/22/2021

2 answer

Which are the right configurations in the Markov chain of a Hamiltonian Monte Carlo algorithm?

I have a question about the Markov Chain Hamiltonian Monte Carlo (MCHMC).Hamiltonian Monte Carlo is known as Hybrid Monte Carlo too. I'll describe the steps of the algorithm.We have...

Asked on 08/22/2021 by Eleuname

1 answer

Random access random permutations

I have a large number of parallel processes and a large integer $n$, and want to randomly partition the integers $[0,n)$ among the processes with only $O(1)$...

Asked on 08/22/2021 by Geoffrey Irving

1 answer

Looking for Runge-Kutta 8th order in C/C++

I would like to use Runge-Kutta 8th order method (89) in a celestial mechanics / astrodynamics application, written in C++, using a Windows machine. Therefore I wonder if anyone knows...

Asked on 08/22/2021

4 answer

Constructing explicit Runge Kutta methods of order 9 and higher

Some older books I've seen say that the minimum number of stages of an explicit Runge-Kutta method of a specified order is unknown for orders $geq 9$. Is this still...

Asked on 08/22/2021

2 answer

In FEM, why is the stiffness matrix positive definite?

In FEM classes, it's usually taken for granted that the stiffness matrix is positive definite, but I just can't understand why. Could anyone give some explanation? For instance, we can...

Asked on 08/22/2021

2 answer

Parabolic differential equations with time delay

Let $d_1=1,d_2=2,a_{11}=frac{5}{13},a_{12}=frac{22}3,a_{21}=-2,a_{22}=frac{6}7,tau=frac{5}7$, $psi(t,x)=cos^42x,phi(t,x)=frac{3}{13}x^4sin^2 3x$, $Omega=[0,200]$ How to solve: $$left{begin{array}{lc} dfrac{partial u(t,x)}{partial t}=d_1triangle u(t,x)+u(t,x)left(r_1-a_{11}u(t-tau,x)-a_{12}v(t,x)right),& t>0,xinOmegadfrac{partial v(t,x)}{partial t}=d_2triangle v(t,x)+v(t,x)left(-r_2+a_{21}u(t,x)-a_{22}v(t,x)right),& t>0,xinOmegadfrac{partial u}{partial n}=dfrac{partial v}{partial n}=0,quad tge0,xinpartialOmega quad(text{Neumann conditions})u(t,x)=phi(t,x)ge...

Asked on 08/22/2021 by LCFactorization

1 answer

Numerically finding constants of motion

Given a set of ODE's $ dot{z} = f(z) $ (or discrete time $ z_{t+1} = f(z_t) $), is there a way to numerically find constants of motion? For $...

Asked on 08/22/2021

3 answer

Numerical packages to solve Volterra integral equations

I am looking for numerical packages (ideally Python) to solve second kind Volterra integral equations, such as $$u(t)=g(t)+int_0^tK(t,s)u(s) ds$$ or Volterra-Fredholm integral equations $$u(x,t)=g(t,x)+cint_0^tint_Omega K(t,s,x,xi)u(s,xi) dxi ds$$ Are there any...

Asked on 08/22/2021

1 answer

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_{21} + n_0(t)W_{01}(t)...

Asked on 08/22/2021 by M. Douglas

1 answer

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