Stack Exchange Network

Stack Exchange network consists of 174 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

Visit Stack Exchange

Questions tagged [nonlinear]

Used to mark questions about nonlinear differential equations, `NonlinearModelFit`, and related to nonlinear dynamics.

-2
votes
2answers
58 views

Solving a 2nd-order nonlinear differential equation [on hold]

My equation is [{x[t]*x'[t])'-(F/m)+(b/m)*x(t)*x'(t)==0},x(0)=0,x'(0)=0] It is a form of Newtons momentum equation, but I am having a lot of trouble solving this ...
0
votes
3answers
42 views

How to get the Roots of nonlinear equations

How to get the Roots of nonlinear equations. nu=326.531 Plot[(I*m1)*Tanh[I*m1] - nu, {m1, -1, 30}] How to get the first ten positive roots and i have tried ...
0
votes
1answer
48 views

Fitting data using a parametric differential equation

I was fit the data using differential equation(eqns) and pfun I tried data fitting (I gave the parameter directly..a=22500, b=10^-22, c=2*10^-40 and scaling factor k=1.04 10^-36) ...
1
vote
1answer
54 views

ParametricNDSolve[] for Double Damped Pendulum

I am trying to plot Driven Double Pendulum with a control Parameter "Gamma". My understanding is that as this gamma approaches a critical value, the pendulum is pushed towards non-linear regime, and ...
1
vote
2answers
38 views

How to reduce the residue in NSolve for a system of 3 non-linear equations

I have written the following snippet in Mathematica to solve a system of 3 non-linear equations? ...
2
votes
2answers
175 views

Solve PDE with complicated coefficient non-linearity [closed]

I wish to solve is the heat equation with solution-dependent coefficient. The equation along with BC's and IC's are as follows: $\begin{equation} \frac{\partial P[x,t]}{\partial t}-\alpha[x,t]\frac{\...
3
votes
0answers
45 views

Plotting gradient and newton directions for parametric system of nonlinear ODEs

I have a bucket (system) of chemical kinetics models, a nonlinear dynamical system given by: where kf >= 0 and kr >= 0 are the parameters. The initial conditions are A(0) = B(0) = 1 and C(0) = 0. I'...
2
votes
2answers
68 views

Plotting solution to Differential Equation with separable variables [closed]

Got this differential equation $$y'=\frac{-x^2(y+1)}{y^2(x-1)}$$ If I try directly to DSolve it ...
0
votes
0answers
50 views

Why does DSolve return the same DSolve expression?

I am trying to find the closed solution for the classic chemostat model with one species and one resource (Monod response) using the DSolve() function. However, after running for 10 minutes, I get ...
1
vote
1answer
85 views

ODE which can be solved without parametrisation [closed]

I want to solve the following differential equation, which can be solved without parametrisation $\qquad y^2y'^2-2xyy'=x^2-2y^2$ I need the solution for my student research project. When I try to ...
3
votes
2answers
151 views

NDSolve:Coupled PDE's, initial-boundary value problem: unreasonable “insufficient number of boundary conditions” error

I tried to NDSolve the PDE system: $$\partial_t y = x\partial_z w \quad\quad \partial_t w = \partial_z y \quad \quad \partial_z x=w $$ for $$(t,z)\in[0,1]\times[-1,0]$$ with initial conditions $$x(...
0
votes
1answer
77 views

How to plot phase portiere and the solutions of ODES

Dear All I know how to plot phase portrait for the system of nonlinear odes but I did not know whey the result of Show the parametric solutions with phase ...
0
votes
1answer
46 views

Forcing a 2D nonlinear fit through a set of points

I am trying to fit a set of data points using exponential functions as the underlying process suggests an exponential decay. The data points are: ...
1
vote
1answer
52 views

Plotting a nonlinear damped pendulum with adjustable damping variable

I am trying to graph the formula of the angle of a damped pendulum over time which starts at an angle pi/3 with 0 angular velocity. The angles used are too large to make use of the small angle ...
1
vote
2answers
64 views

Solving non-linear PDEs

I wish to solve the equation $$\frac{dp(x,y,t)}{dt} = D\ \nabla^2 (p(x,y,t)) -C \ p(x,y,t) - R \ p(x,y,t)^2 $$ But, I get the error ...
1
vote
2answers
119 views

Getting error NDSolve::ndsz from my ODE

I'm trying to figure out why I am consistently getting singularity error when I'm trying to solve an ODE using NDSolve. Any help will be appreciated. ...
2
votes
2answers
118 views

Newbie PDE Question

I downloaded Mathematica trial in order to try to solve a PDE that Matlab symbolic couldn't handle. I don't know all the bells and whistles but going along with online documentation. I am trying to ...
3
votes
1answer
83 views

Problem involving a system of nonlinear coupled ODE's with adjustable boundary

The problem is to solve the following system ODEs: I. $\ \ \ \ \ \ \ \dfrac{4}{r}[1+a(r)]\left(\dfrac{dH}{dr}\right)^2+\dfrac{dG}{dr}=0$ II. $\ \ \ \ \dfrac{1}{r}\left(\dfrac{dA}{dr}\right)+f(r)+k^...
2
votes
1answer
30 views

`Reduce` yields `False` although solution exists

This is the first time I use Mathematica, and I wonder how to use Solve and Reduce. The following code is taken from a geometric ...
0
votes
1answer
73 views

Solving a system of non-linear equations with four unknowns and two parameters

I need to solve a relatively simple system of 4 non-linear equations with 4 variables (a, b, p, q) and 2 parameters (λ, μ). If ...
2
votes
2answers
58 views

NDSolve producing message Power::infy

I am trying to solve geodesic equations in some 3D black hole spacetime. It is a coupled ODE system with boundary conditions. Due to the symmetry of the spacetime, I expect the solutions to be even ...
3
votes
1answer
73 views

Solving a non-linear system of equations given $1000$ data points

I have a vector of $1000$ data points saved in a vector $y$ and I need to solve a set of non-linear equations. Since I cannot write down all $1000$ values, I will assume that I have the following data ...
0
votes
3answers
112 views

Using WhenEvent to Change the Sign of a Constant

I am attempting to change the sign of a constant when a certain condition is met during a numerical integration. Here is the code: ...
4
votes
0answers
98 views

DSolve, NDSolve with WhenEvent Give Incorrect Solution for Simple ODE

NDSolve Results On the course of addressing question 181974, I encountered the following problem. ...
1
vote
1answer
167 views

Solving nonlinear ODE with boundary conditions

I am trying to solve the below fucntions using a NDsolve, but I can't get the the converges of them at the certain initial variables.I'm using Mathematica 11.3. I appreciate any help. ...
1
vote
2answers
95 views

Stability of collinear Lagrange points

I am currently simulating the restricted 3-body problem in Mathematica. I have identified the Lagrange points and their coordinates. Now I want to see how particles move in their vicinity, to check ...
3
votes
2answers
106 views

Solving an 'odd' differential equation with NDSolve

I need to solve a differential equation of the type $\qquad \partial_{x_1}y(x_1,x_2)= y(x_1,x_1)\,y(x_1,x_2)$ with initial condition $\qquad y(0,x_2)=x_2$. Now if I try to solve this with NDSolve ...
5
votes
4answers
118 views

Defining system of Equations

I am not able to define a system of n equations having n variables x1, ...
8
votes
2answers
156 views

Proper use of NDSolve in the context of the reduced 3 body problem

I am currently trying to solve the reduced three body problem in Mathematica. I have the equations of motion $\ddot{x}-2\dot{y}=-\frac{\partial\Omega}{\partial x } $ $\ddot{y}+2\dot{x}=-\frac{\...
0
votes
1answer
78 views

Non-linear optimization giving error NMaximize::nrnum [closed]

I am trying to solve the following non-linear optimization problem: Here is my code: ...
1
vote
1answer
93 views

How can I solve a certain complicated second-order PDE?

I am trying to solve the following complicated second-order PDE ...
6
votes
0answers
149 views

DSolve Returns Incorrect Solutions for First-Order ODE

Bug introduced in 10.4 or earlier and persisting through 11.3. Reported to Wolfram Technical Support as CASE:4150361. Fifty-one DSolve questions on this site are ...
1
vote
1answer
183 views

Solution of nonlinear system with boundary conditions

I'm try solve the following coupled ODEs with boundary conditions: $I. \ \ \ \ \ \ \ \dfrac{4}{r}[1+A(r)]\left(\dfrac{dH}{dr}\right)^2+\dfrac{dG}{dr}=0$ $II. \ \ \ \ \dfrac{1}{r}\left(\dfrac{dA}{dr}\...
0
votes
1answer
134 views

Mathematica returns DSolve exactly as I gave it [duplicate]

I'm trying to solve a set of coupled differential equations as follows: ...
2
votes
1answer
96 views
0
votes
1answer
49 views

Nonlinearfit with incomplete data

Suppose I have an ODE model and some incomplete time series data data = {{0,1},{5,6.2},{14,18.4},{28,57.3},{90,105.2},{180,98}} My question, can I still use ...
3
votes
2answers
186 views

Nonlinear system of ODEs with boundary conditions

I'm trying solve this problem: g'(r) = a(r)g(r)/r, (1/r)a'(r) = g(r)^2-1 which have the following boundary conditions: a(0)=n ...
2
votes
2answers
80 views

Problem using NonlinearModelFit to 2 coupled differential equations

I am trying to find the parameters of a set of differential equations given experimental data. Before I tackled my set of 12 equations, I tried to solve a simpler and similar 2 equation system but ...
4
votes
1answer
162 views

Inviscid Burgers equation — multivalued wave

I'm quite new to Wolfram Mathematica. I need to create an animation of a Burgers Hopf equation's solution which becomes multivalued (somewhat of a breaking wave). Is it possible to do so in ...
1
vote
1answer
202 views

Solving Integro-differential equation numerically with shooting method

This question is related a question I previously asked here Solving integro-differential equation with boundary condition at infinity and for which a solution was found . Now I am dealing with a ...
0
votes
1answer
151 views

No output for bifurcation diagram

I am plotting a bifurcation diagram for my system with A on x-axis following the code in, How to make a bifurcation diagram of the Lorenz system under a varying ...
0
votes
2answers
165 views

Nonlinear model fit with Numerical integration

I'm having trouble writing a Nonlinear Model fit where the model is a numerical integral evaluated with NIntegrate. I have read other questions and answers about more or less the same problem, but for ...
1
vote
1answer
62 views

Improving nonlinear model fit (piecewise function)

I have a piecewise relatively simple function, and I'm looking for three parameters. Here's an MWE: ...
0
votes
1answer
29 views

NonlinearModelFit doesn't work as a function

I use a NonlinearFitModel operation for fitting the piecewised data, and then want to use the result of operation as a function. However, it doesn't work. Could anyone please tell me where can be a ...
2
votes
0answers
37 views

Is there any reason to use FindFit over NonlinearModelFit? [duplicate]

Given that FindFit seems to just be able to return estimated coefficients and none of the other goodies (standard errors, confidence bands, residuals, etc.), under ...
1
vote
2answers
131 views

A problem in bifurcation diagram

I have the following problem ...
0
votes
1answer
109 views

Problem plotting a bifurcation diagram

I have been trying to plot bifurcation diagram for $R$ vs $X$ (or $Y$) for the following problem ...
3
votes
2answers
261 views

Solving integro-differential equation with boundary condition at infinity

I wish to solve a differential equation that contains a hard-to-evaluate integral and to plot the solution in a range at least $r\in(0,10)$. The equation comes from a Hartree equation (Schroedinger ...