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

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0
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75 views

Boundary conditions for NDSolve

I get the following message: Boundary values may only be specified for one independent variable. Initial values may only be specified at one value of the other independent variable. >> from ...
0
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1answer
35 views

An unexpected NDSolve behavior [closed]

I observe the following. The code: ...
0
votes
1answer
58 views

Setting Initial Conditions in a System of Differential Equations that don't start at t=0

I have a system of six differential equations (linear for the sake of the discussion). I want to set the initial condition to start at time t=18 and not time t=0. I know the values of the dependent ...
0
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0answers
37 views

Solving Time-Dependent PDE's Analytically with no non-trivial Boundary Conditions

I'm having some trouble solving a partial differential equation that is supposed to model the propagation of a scalar field in Schwarzschild spacetime using spherical coordinates. I'm using the DSolve ...
6
votes
0answers
50 views

EventLocator in NDSolve seemingly hogs memory in Windows, but not Mac

I have written a function (ftest in my code) which does the following: Takes a vector {x,vx,vy} as input Numerically solves (with high precision) a specific ...
11
votes
1answer
250 views

NDEigensystem returns incorrect eigenvalues for 2D coulomb problem, eigenfunctions contain discontinuity

I posted a similar question a short time ago regarding the 3D Coulomb problem. Jens' excellent answer to this thread allowed me to obtain the correct eigenvalues and eigenenergies for that system. I ...
4
votes
1answer
100 views

Issues with modeling pulses in a very simple system of DAEs

Bug introduced in 10.4.1 or earlier Bug has been confirmed by WRI [Case:3594387]: It does appear that the NDSolve function is not behaving properly in this case and an incident report has been ...
0
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1answer
71 views

How to perform this nth derivative operation in MMA?

I have to solve this following equation where I need to differentiate a function $n$ times. $$A=\sum_{n=0}^{m-1}\frac{s^n}{n!}(-1)^n\frac{d^nf(s)}{ds^n}$$ How to express the above equation in ...
0
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0answers
38 views

Recycle boundary condition

I'm having the following issue that can not find a solution , by using this boundary condition u[0, t] == 2 u[1, t] that Mathematica does not understand, someone ...
1
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0answers
48 views

Solving ode which solution oscillate violently

This is a ordinary differential equation: y[x]/(-1 + x^4)^2 - ((1 + 2 x^2 + 3 x^4 - 2 x^6) Derivative[1][y][x])/(x - x^5) + Derivative[2][y][x] == 0 I want to ...
0
votes
2answers
84 views

Jump boundary conditions

I'm having the following issue that can not find a solution , by using this boundary condition ...
1
vote
0answers
82 views

How to “INJECT” with holding Evaluation, specifically into a WhenEvent

I am importing a set of differential and stochastic equations from an external package, and want to use Mathematica to analyse this. I am struggling building the set of equations that I can use with <...
0
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0answers
41 views

Pass List / Vector argument through NDSolve to a function

I am trying to pass vector or list as argument to the function from NDsolve.And I am getting these error. Also I am pretty new to stack overflow. Apology if this a possible duplicate. Here is my code. ...
1
vote
1answer
44 views

portions of plot missing for a relatively simple function

I am trying to produce a graph of the linear dynamic system response to a step input. The code is as follows: ...
0
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2answers
88 views

Free-fall air resistance problem

I´m working on a free fall problem and I got an equation with variable $k$ when the situation has air resistance. Then I compared with no air resistance equation ($-4.9$, considering t variable). So, ...
9
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1answer
76 views

How can I identify which solution triggered the WhenEvent?

I am using NDSolve for problems like this: ...
3
votes
0answers
44 views

Constraining Function to be positive with NDSolve, Allee effect

I am trying to numerically solve the steady-state behaviour of the Allee effect (with one spatial dimension, diffusion): $\frac{\partial n}{\partial t} = D \frac{\partial^2 n }{\partial x^2} + rn\...
3
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0answers
80 views

Kernel crashes when computing finite difference mixed derivative with respect to y & z but works fine when computing with respect to x & y or x & z?

I am using Mathematica 10.4.0 on Ubuntu 16.04. I am trying to solve a set of differential equations using finite difference method on an NxNxN cubic grid (x, y, z directions). I am getting a weird ...
5
votes
1answer
75 views

Finding the correct boundary conditions to a specific problem

I want to reproduce the following problem in the figure: $$\phi''+c\phi'\sqrt{m^2\phi^2+\phi'^2}+m^2\phi=0$$ where $\phi=\phi(x)$ with $x \in (-\infty,\infty)$, $c=\sqrt{3/2} \ $ and $m=0.2$. ...
3
votes
2answers
110 views

Switching Differential Equation in NDSolve

I am trying to solve the following system of differential equations using NDSolve: $\dot{z}_t=.5(1-z_t)$ $\dot{y}_t=.05y_t+z_t-x_t$ subject to the following constraint: $-y_t-z_t\le0$ where $z_t$ ...
10
votes
1answer
237 views

NDEigensystem cannot solve numerically the 3D Coulomb problem, while DSolve returns the right answer

After having derived by hand the eigenvalues and eigenfunctions for the 3D and 2D hydrogen atom, I want to solve the systems numerically using Mathematica. I need to do this because my next step is to ...
3
votes
2answers
107 views

Assigning Element Markers to 3D FEM Mesh

I have created a 3D graphic using GraphicsComplex and then use ToElementMesh to generate a 3D Mesh that I want to solve a PDE on, but I cannot figure out how to apply ElementMarkers to the Boundaries. ...
3
votes
2answers
177 views

Solving coupled differential equations with unknown constants

Is it possible to obtain exact solutions of these types of coupled differential equations directly in Mathematica ...
1
vote
1answer
224 views

Solving wave PDE

I am trying to solve the wave PDE with NDSolve. Below is the equation: ...
0
votes
1answer
95 views

Using Neumann boundary conditions

I had a semi-related physics problem I needed to solve analytically (which I have already done), but I am now curious how I would go about numerically solving the entire system in Mathematica. ...
0
votes
1answer
52 views

Epilog not working [closed]

When I run the following code ...
0
votes
0answers
46 views

Problems with numerical solution of differential equation

I'm trying to obtain a numerical solution for my differential equation. But i have the following mistake: Encountered non-numerical value for a derivative at z == 0. Can somebody help with that? <...
2
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1answer
137 views
3
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2answers
85 views

DiscretizeRegion does not include the boundary specified in ImplicitRegion (10.1)

I am trying to do some 3D PDE solving, and I keep running into problems with boundary conditions because my meshed boundaries are not what I expected. For example, the following code ...
8
votes
2answers
333 views

Lagrangian to Hamiltonian

I want to go from Lagrangian description to Hamiltonian one. Using the example given by Mathematica I do something like: ...
0
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0answers
48 views

Fitting 6 differential equations to 6 sets of data

I am using the newest Mathematica and I am trying to fit a set of 6 linear differential equations to a set of experimental data for each of the six variables. I am a baby beginner at this and could ...
2
votes
3answers
114 views

Strong glitch with Evaluate in Manipulate

I'm experiencing a strong evaluation problem for a Manipulate box and I can't find the best solution yet. Here's a MWE to show the glitch : ...
2
votes
0answers
91 views

NDSolve for unsteady Taylor-Goldstein equation, can't use MethodOfLines

I am trying to solve a relatively simple system of linear PDE in two variables (z,t). The equations are basically the Navier-stokes equations linearized around a constant background velocity profile ...
0
votes
0answers
45 views

Impose conditions on differential equations

This is my first post in Mathematica Stack Exchange, so thanks for your help and sorry for any rookie mistakes. I am solving the Einstein equations for two vectorial pertubations h_Alpha and v_Alpha ...
3
votes
1answer
218 views

NDSolve mixing many scalar and vector equations

I have a set of scalar equations in many unknowns, which I want to combine with a vector equation inside an NDSolve. The equations are a mix of differential and algebraic equations. A set of scalar ...
1
vote
1answer
47 views

“MemoryAllocationFailure” in DSolve

Mathematica 10.4, Windows 10, 6 GB RAM, 64 bits When I trying to solve DSolve[{v'[t] == 100 - 0.15 v[t]^2, v[0] == 30}, v[t], t] I get ...
14
votes
2answers
324 views

What can one do with extremely stiff problem in NDSolve?

Consider the following illustrative problem: $$ \frac {\partial f} {\partial t} = \frac {\partial} {\partial x}(x f) + \frac {\partial} {\partial x}(f \frac {\partial f} {\partial x}) $$ This is ...
2
votes
1answer
46 views

Clearing Problem with DSolve

Consider: This is a classic mistake (using a single equal sign) that has been discussed on Mathematica Stack Exchange before. I know that Clear[Derivative] will cure the problem. However, consider ...
0
votes
1answer
41 views

NDSolve point animation not working [closed]

The below code plots the path of a ball bouncing but loses 90% of its velocity each time it bounces. (adapted from https://reference.wolfram.com/language/ref/WhenEvent.html). ...
0
votes
1answer
59 views

I am having trouble with the DSolve function [closed]

DSolve[{x''[t] + 0.01 x'[t] + x[t] == E^(It), x[0] == 1, x'[0] == 1}, x[t], t] This give the following error :"Equation or list of equations expected instead ...
2
votes
0answers
66 views

How to change the boundary condition near singularity

The following system has a singularity around $x=0.451$. What I want to do is to detect when the solution gets close enough to this singular point (in this example I'm using the threshold of $0.001$), ...
1
vote
0answers
55 views

DSolve does not give an analytic solution for a tutorial input [closed]

I am just starting with Mathematica and I have tried to solve PDE following DSolve, with first three inputs from the Elliptical Partial Differential equations ...
0
votes
0answers
68 views

Nonlinear PDE system in a rectangle

This question is posted by two physics students working together. We are having some trouble while trying to solve Navier-Stokes equations, The main problem is that, while our set of partial ...
0
votes
1answer
102 views

Plotting graphical analysis of chaotic behavior

I am trying to plot some results of chaotic behavior in a system based on a paper for one of my classes. I am a physics undergrad. I found some sample code online springy.nb which I have been trying ...
0
votes
1answer
93 views

How to omit the corrupt value in a program?

I've such errors: Coordinate .. is not a floating-point number and can't correctly fix it. The problem occures when x==Log[2] The program works correctly ...
0
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0answers
39 views
2
votes
1answer
127 views

Differential Equation with Numerically Integrated Boundary Conditions

I have a second order differential equation that I'd like to solve numerically, and then integrate its solution twice to get the parametric equations of a curve. The ODE is: $2 \kappa''(s)+\kappa^3(s)...
0
votes
0answers
65 views

solving system of ODEs in Mathematica

I am using the DSolve to solve the following 2 ODEs \begin{equation} \begin{cases} &\dot{y}(t)=z(t)-y(t)-\frac{c_1c_2y(t)}{-c_1c_2e^{-t}t+c_1(1-c_2)+c_3e^{-t}}\\ &\dot{z}(t)=-z(t)+\frac{...
3
votes
1answer
72 views

Dsolve svars error: Equations may not give solutions for all “solve” variables

New to Mathematica, trying to solve a set of coupled differential equations related to a geodesics/Calculus of Variations problem. More specifically, I am trying to solve the two Euler-Lagrange ...