# Tagged Questions

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

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### Variable name complication with DSolve? [closed]

I'm trying to run the code: ...
64 views

### How can I get a list of solution points from NDSolve?

I just need a list of numerical solutions for x[t], x'[t], x''[t]. While I know how to graph ...
137 views

### Ito Process paths over a Plot3D

I was wondering if its possible to draw the simulated paths of an Ito diffusion over the probability density function. Ito Process: ...
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### 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: ...
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### 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 ...
144 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 ...
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### 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 ...
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### Changing variable in numerical solution

I solved numerically the differential equation: ...
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### 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, ...
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### 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: ...
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### 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/...
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### 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 ...