# Tagged Questions

Questions on the symbolic (DSolve, DifferentialRoot) and numerical (NDSolve) solutions of differential equations in Mathematica.

49 views

### Manipulate with DSolve

I have defined a set of differential equations stored in sol and I'd like to plot them while being able to change the parameters. I've tried it like so: ...
71 views

### Heat Conduction where thermal diffusivity depends on z

I'd like to know why Mathematica is not solving this problem for me. Let's imagine a body in which the thermal diffusivity varies with z (we have a cyllindrical ...
143 views

### Result interpretation of a general solution of a nonlinear differential equation

My goal is to find the general solution of the following nonlinear differential equation: $$x'(t) = e^{-t} - \sqrt{x(t)}$$ Following this guide, I've entered in the Wolfram Mathematica the following ...
55 views

### Improve speed of RK4 algorithm for solving ODE

For anyone with interests in dynamical system, i'm trying to plot the phase space of a given hamiltonian. My code is this: ...
109 views

### failure of code with Helmholtz equation with point source

I am new to the finite elements package in Mathematica. I have a system of equations, one of which is a Helmholtz equation with a point source in the interior of a bounded domain. The following is the ...
35 views

### Changing variable in numerical solution

I solved numerically the differential equation: ...
78 views

### Can I use operators of the form $\frac{d^2}{dx^2}+i\frac{d}{dx}$ inside NDEigensystem?

I am currently trying to find the eigenfunctions of Hamiltonians of the form $\hat H=\frac12 \hat p^2 +a\hat p +f(\hat x)$, and I thought I would give NDEigensystem ...
91 views

### Different results from ode45 and NDSolve?

I am solving nonlinear ODE + integration groups using NDSolve of mma and ode45 of matlab. At last, I found that they give different results, even after I added RungeKutta method, interpolationorder, ...
47 views

### Naive question on ODE numerical solving and periodic initial conditions

I have a second-order nonlinear ODE for which I would like to find a numerical solution, with periodic initial (boundary) conditions. Can this be done directly with ...
51 views

### NDSolve for complex variables

I am trying to simulate a multiple pendulum system with damping as follows: ...
89 views

65 views

### Error message when running NDSolveValue

I am trying to solve a set of differential equations but keep getting an error. See message below "NDSolveValue::ndnum: Encountered non-numerical value for a derivative at t=0" The system that I ...
127 views

### How to plot an Eddington-Finkelstein diagram

I need to plot the same thing as what is shown on the third picture of the site below (sorry, I'm unable to poste that picture here) : http://ion.uwinnipeg.ca/~vincent/4500.6-001/Cosmology/...
130 views

### NDSolve and differentiation of Abs

I have found several questions about the derivative of Abs and how it is not defined in the complex plane. What I have not found yet is a precise and simple ...
68 views

### Neumann and Dirichlet eigenvalue problem - Eigenfunctions on the square [closed]

I don't know if I am in a good place to ask my question, but I'd like someone to create a visual support for a problem of mathematics. I was wondering what is the fundamental different between a ...
87 views

### Stop Integration in NDSolve

The following code executes properly for some choices of initial points and parameter c, but fails for other choices. Could the failure be due to computation outside of the defined t, x, and y ranges? ...
263 views

### Ion motion in uniform axial magnetic field and radial electric field [closed]

I'm trying to model an ion's 3D motion in a constant/uniform axial magnetic field and a radial electric field (similar to a cylindrical magnetron, but two positive parallel center electrodes offset by ...