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

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1
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1answer
70 views

Variable coefficient Differential Equation

Can anyone help with the following differential equation. The errors i am getting are also given. ...
0
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1answer
206 views

Solution of differential equation in terms of incomplete gamma function

I need help in solving equation 15 and 16 either manually or in Mathematica to get the solution in terms of the incomplete gamma function. This is what Mathematica tells me. I can't understand ...
0
votes
1answer
58 views

NDSolve and a vector function [duplicate]

I'm trying to solve a set of differential equations which include a numerical function that takes a vector and returns a vector. ...
0
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1answer
129 views
0
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1answer
52 views

Reduce in NDSolve [duplicate]

Second order ode; neither the trig RHS simplifies nor is the solution obtained readily: ...
1
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0answers
49 views

How to use interpolating functions in NSolve with a piecewise function?

I have a system of two non-linear differential equations that are piecewise, the solutions of which I would like to use to obtain the values of a third variable that is also piecewise. I have trouble ...
2
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1answer
214 views

Getting errors NDSolve::nlnum, NDSolve::icfail)

I would like to plot the function v[r], and resolve this differential equation in spherical simmetry: ...
6
votes
3answers
138 views

Force WhenEvent to respect default stepsize

I have to numerically integrate an equation system and monitor the accumulating datapoints. For example, I fit a line to a subsample of the points and terminate via ...
1
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1answer
113 views

Problem with solving a system of differential equations [closed]

I am trying to reproduce a result that is part of a derivation of the flow due to a rotating disk. I have as given this system of differential equations. (In these equations primes indicate ...
11
votes
4answers
363 views

periodic boundary conditions and NDEigensystem

Mathematica 10 has a splendid new function, NDEigensystem, that makes it possible to solve Sturm-Liouville problems numerically in a single step. I have not however been able to find a way to get it ...
0
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0answers
46 views

ndsz : step size is effectively zero; singularity or stiff system suspected

This is the first time I ask a question. I have seen many solutions to this error and tried but they are not working. Here is the code. Needs["DifferentialEquations...
3
votes
1answer
173 views

How to work with ParametricNDSolve?

Update 3: I got it. A small dumb mistake... It has to be Evaluate[xP[y]'[0] /. s10] like this. Oh well... Update 2: So if do this ...
0
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0answers
46 views

Output of NDSolve is useless when the system gets bigger

I have a bridge, which I want to discretize on $n$ stiff rods. To find a solution I wrote the following code in mathematica: ...
-3
votes
1answer
78 views

How to implement Bifurcation of delayed Lorenz system? [closed]

The delayed Lorenz system is as follows: (Bifurcation parameter as $\tau$) $$\begin{align*} D^\alpha x_1(t) = & a_1(x_2(t-\tau)-x_1(t)) \\ D^\alpha x_2(t) = & a_2x_1(t)-x_2(t)-x_1(t)x_3(t) ...
0
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0answers
87 views

NDSolve with default settings solves much faster than classic Runge-Kutta 4

NDSolve with default parameters takes 0.25 s for the first run. With Runge Kutta 4 specified, it takes about 4.6 s, ...
3
votes
0answers
53 views

EvaluationMonitor slows down NDSolve considerably

Hi guys I'm solving a nonlinear system of ODEs with NDSolve. Since the dimension of the system ranges from 2700 to 20000 equations, depending on the parameters, the time required to solve the entire ...
0
votes
1answer
515 views

Applying l'Hôpital's Rule to NDSolve with Piecewise Function

OK, so I've been working on this problem for over a week and it's driving me crazy. I'm trying to solve a system of two differential equations in $x(t)$ and $y(t)$ using a "time-elimination method," ...
0
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0answers
64 views

How to systematically approach when solving a large system of differential equations?

I defined several functions in order to get to the final system of a partial differential equations I have to solve. Here is how I did those definitions: ...
0
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1answer
79 views

Proper way to produce StreamPlot

I have faced with problem of not completely correct phase trajectories of ODE, which was produced by StreamPlot. Next following code ends up with this plot: ...
3
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0answers
54 views

Singularity treatment in a simple problem [duplicate]

With a simple search, several posts can be found on treating singularities encountered while using NDSolvefamily of numerical methods. However, most of them involve ...
1
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2answers
64 views

If statement, differential equation

I've got problem with If statement. It doesn't work. I've never used Mathematica before, probably it's a problem with syntax. ...
1
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2answers
232 views

Differential equation and For loop in Mathematica

I'm trying to optimize some kind of process in Mathematica. I did it without any problems in Matlab and now I'm trying to do the same in Mathematica which I don't know at all. I'm trying to find the ...
1
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0answers
34 views

wrong sign with NeumannValue

I want to use NDSolveValue with Neumann boundary condition. The documentation says this https://reference.wolfram.com/language/ref/NeumannValue.html . In the ...
5
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0answers
92 views

unhandled win32 exception in WolframKernel.exe in DSolve of non-linear ODE in one variable

Bug persisting through 10.4. (windows 7, 64 bit) Installed 10.3.1 and started to run some old ode's. in V 9, this ode used to return unsolved, which is ok, but in 10.3.1 now the kernel crashes. ...
1
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1answer
76 views

How to plot an Ordinary differential equations

Hey guys I'm using mathematica 5 now, and so new to this software thing. May I know how to plot the direction field using PlotVectorField[] and also finding ...
0
votes
1answer
97 views

NDSolve coupled Non Linear differential equation, Obtain solution

Trying to solve a coupled differential equations of motion. When there is no Working Precision mention it runs and give following plot for θ[t] but this is wrong, θ must be symmetric about 0. ...
1
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0answers
40 views

NDSolve with (approximately continuous) Piecewise input

I am finding some troubles when using NDSolve with this piece of code: ...
0
votes
1answer
30 views

WhenEvent StopIntegration not working [closed]

I am trying to use a WhenEvent to StopIntegration when Tmelt=1356 is reached. Although the NDSolve appears to be working, "StopIntegration" is not stopping the integration and no value is given for ...
3
votes
1answer
68 views

NDSolve with an interpolating function in Piecewise

Again I have question I hope someone can answer. I made a very simple example illustrating my more difficult problem. I want to solve a differential equation numerically with a conditional in the ...
4
votes
2answers
203 views

General solution for a linear ODE set with complicated coefficient

This is the original problem that motivated me to ask this question. I encountered it when trying to reproduce the deduction in this paper. (I'll paste the relevant part below to make this question ...
19
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2answers
840 views

Phase portrait on a cylinder

It is very nice and very easy to make a sketch of a phase portrait with StreamPlot. For example, for the classical pendulum, defined by \begin{eqnarray*} \dot ...
2
votes
1answer
84 views

System of differential algebraic equations with one of the variables as an argument of the other varaibles

This is my first question here and I don't even know what to search for to find a solution. So I'd appreciate it even if someone can point me in the right direction. EDIT: My post had many problems, ...
0
votes
1answer
82 views
0
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0answers
25 views

Discretization of a region for NDSolve using [duplicate]

I would like to mesh the region below in order to use it for a calculation by means of NDSolve. Could anyone help me to discretize this region for NDSolve using. Thank you very much. ...
0
votes
0answers
191 views

Maximum of NDSolve output. Problem with interpolating function

I solve a NonLinear PDE and get a solution (which for other reasons I put into a vector): SolVec1[1][[2]][x,t], where x and t are the indipendent variables. Now, I would like to get a distribution ...
0
votes
1answer
69 views

Difficulty using NDSolve

I am tying to solve two differential equations with two delays numerically. The result didn't come out and it was written that “NDSolve::ndsz:...step size is effectively zero; singularity or stiff ...
0
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0answers
37 views

Problems solving differential equation with ParametricNDsolve for certain parameters

I'm working on a simulation of a physical problem for a few weeks now and I'm starting to get really frustrated about it. The problem itself is the stationary case of the heat diffusion equation in ...
0
votes
0answers
22 views

The result didn't come out and it was written that “step size is effectively zero; singularity or stiff system suspected” [duplicate]

I am tying to solve two differential equations with two delays numerically. The input is given by the picture below. I have tried the methods that have been posted in the web but it didn't work. ...
2
votes
1answer
212 views

How can I get the time steps chosen by NDSolve when the Method -> “ExplicitRungeKutta” option is given?

I am trying to solve an ODE with NDSolve using the "ExplicitRungeKutta" method. I need to know exactly which time steps ...
0
votes
1answer
86 views

How to prevent extrapolation in Manipulate? [duplicate]

How can I limit the time slider to the NDSolve solution range in a Manipulate box, so no extrapolation is used ? More specifically, here's a stripped down version of my Manipulate code which shows ...
4
votes
2answers
102 views

Integrating an interpolating function

I have been using the following NDEigensystem command to generate the eigenfunctions of the laplacian with a square domain: ...
2
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0answers
31 views

exe file creation [duplicate]

HOW CAN I MAKE IT exe FILE? PLEASE HELP... ...
0
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2answers
137 views

How can I perform NIntegrate with NDSolve?

I'm a new user and I have no idea how to perform NIntegrate by using NDSolve. For example consider following differential equation (DE): ...
3
votes
2answers
191 views

Plotting the solutions of $y' = -\frac{\cos y}{\sin x}$

I struggle with the problem of plotting the solution of this ODE: $\qquad y' = -\frac{\cos y}{\sin x}$ I've already tried to use ContourPlot in a loop and in a ...
0
votes
1answer
62 views

Can i get step by step calculation of results obtained in mathematica? [duplicate]

In mathematica we generally obtain direct result instead of step by step analytical calculation. Can we somehow obtain these steps?.
8
votes
1answer
175 views

Bug? Problem with derivative of interpolating function from FEM

Bug introduced in 10 or earlier and fixed in version 10.4 I am really not sure if this is a bug or I am missing something very trivial. QUESTION: What I am missing in order to obtain the partial ...
3
votes
1answer
85 views

Trying to find a temperature profile with a nonlinear 2nd order ODE. NDSolve very sensitive to seemingly arbitrary constant

I am trying to solve this differential equation for a heat transfer problem: \begin{equation} kt\frac{\partial^2 T}{\partial x^2} = \epsilon \sigma T^4, \ \ \ T(0) = T_0, \ \ \ \frac{\partial ...
0
votes
0answers
52 views

plot for coupled differential equation?

I have two coupled equations and sol is written in term of function as shown below. but not getting any kind of plot. Can any one help please. Thanks.... ...