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

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0
votes
0answers
60 views

FindFit giving many errors when given model produced by ParametricNDSolveValue

I am trying to use FindFit to determine 7 parameters using 7 differential equations based on data imported from Excel. A sample of the data is: ...
0
votes
0answers
32 views

StreamPlot, ListStreamPlot does not visualize vector field properly [duplicate]

I am reopening my question about empty stream plots. I couldn't find a choice for parameters that would give me a proper stream plot for the following example. ...
0
votes
2answers
105 views

How to display results of NDSolve

I am solving differential equation of second order ...
1
vote
2answers
163 views

StreamPlot, ListStreamPlot scaling issue [duplicate]

The following stream plot is empty and the x-axis exceeds $[-0.1,0.1]$ significantly. StreamPlot[{y, -100000 x - y}, {x, -0.1, 0.1}, {y, -100, 100}] Using ...
1
vote
0answers
55 views

Solving a 4th order PDE (Plate bending) [duplicate]

I'm trying to solve the following PDE but I'm getting this error. The PDE represents the bending of a thin plate. ...
2
votes
2answers
229 views

Attempting to use NDSolve to plot harmonic oscillator solutions

NDSolve[{ (-y''[r]/1880) + (470 (0.04077)^2 r^2 - 48 + 1/(1880 r^2)) y[r] == 0, y[0] = 0, y'[0] = 0}, y, {r, -4, 4}] I use this but get errors and am ...
1
vote
2answers
61 views

Plotting issue for nonlinear de

The following code with varying scaling parameter gives same plot. plz suggest correction. ...
2
votes
1answer
92 views

Singularity while solving PDE

I have to solve a PDE (in the context of the functional renormalization group in physics). I have a function of two variables, $U(l,p)$. I know $U(0,p)=U_0(p)$ and then I have an equation (eq925) that ...
0
votes
1answer
110 views

How to solve this DE?

The previous plot has executed. I have another code. This neither shows error nor shows any plot. ...
1
vote
2answers
115 views

Error NDSolve::nlnum1 from 2nd order ODE with 4 boundary conditions

I want to solve this 2nd order ODE with two initial conditions close to the origin (one to the function and the other to its derivative) and more two similar conditions for an endpoint. ...
7
votes
2answers
159 views

Unexpected warning from DSolve

I'm trying to solve this differential equation with respect to $x$ $$ \frac{d^2y}{dx^2}-\bigg(\frac{dy}{dx}\bigg)^2-\frac{1}{x}\frac{dy}{dx}=\frac{1}{x^2} $$ With boundary condition $y(1)=2, ...
0
votes
2answers
181 views

Solving non-linear differential equation

For my research project I need to solve the following integral ...
0
votes
1answer
106 views

FM NMOR in Cesium with Atomic Density Matrix package [closed]

I am trying to use the atomic density matrix package in Mathematica to simulate FM NMOR in Cesium. The example given in the package is for a specific system from J=1 to J'=0. I am trying to simulate ...
3
votes
1answer
93 views

How to determine the redundant equation in the set of DE?

my problem is messy, and I will use a simple problem to explain my problem. Suppose, we have a set of DE: ...
2
votes
1answer
89 views

Struggling with WhenEvent in NDSolve

I am doing some biological system modeling and trying to use WhenEvent in the initial conditions section of my NDSolve code to allow me to periodically change the value of a parameter (which I've ...
2
votes
1answer
160 views

NIntegrate::inumr: “The integrand `E^(-0.9τ1) DiracDelta[t-τ1] v[t-τ1] x[t-τ1]` has evaluated to non-numerical values ”

I am facing an interesting situation over here. The aim is to solve a system of IVP having an integral over a delay range. Here is my try ...
0
votes
0answers
54 views

ParametricPlot that worked in Mathematica 9 stops working in Mathematica 10

I've updated to Mathematica 10 and I am trying to plot the solution of a system of ODEs and I'm using exactly the same file that used to work in Mathematica 9, but now when I want to plot the solution ...
0
votes
0answers
67 views

Second Order ODE (Bessel Function) with a dependent variable in the BC

I have obtained an analytic solution to the following problem however I lack the knowledge to generate a numerical solution using mathematica. I'm reaching out to get an idea of what functions I may ...
3
votes
0answers
51 views

Does NDSolve automatically simplify the system of equations for Hermitian matices?

I am currently starting to solve numerically a system of differential equations like this: $\dot{A}(t)=S(A)A(t)$ Here, the matrices are of dimension $d\times d$. $S(A)$ is some superoperator that ...
2
votes
2answers
173 views

Strange behavior in ContourPlot?

I'm have a Abel's differential equation: ...
7
votes
2answers
228 views

How to locate the position of a periodic orbit

These are the equations of the dynamical system ...
1
vote
2answers
107 views

Can't NIntegrate my NDSolve results

I want to NIntegrate my NDSolve result. I don't have a exact function form because it is coming from the ...
9
votes
1answer
207 views

DSolve documention on web differs greatly from distributed MMA 10.2.0 version

In the course of improving my answer to 95361, I noticed that the DSolve documentation on the web is much better written than that distributed with Mathematica ...
4
votes
4answers
256 views

Trying to model a chemical reaction - NDSolve::litarg error

I am trying to model a chemical reaction with NDSolve. I have specified the known differential equations and parameters, ...
2
votes
2answers
170 views

DSolve gives an empty solution set to a solvable ODE

I really hope this isn't a duplicate, today I was answering this question and was to lazy to solve the quadratic equation on my own and so just asked mathematica to give me the solution of the ...
2
votes
3answers
490 views

Plotting a Bifurcation diagram

I have the following system equation v'(t)=2*G*J1[v(t-τ)]cos(w*τ)-v(t) How do you plot the bifurcation diagram, τ in the x ...
0
votes
0answers
39 views

Paramtric plot for 3 variable system

I have an system where I have calculated migration of "i" number of species "c" in "j" different habitats as a function of time. ...
2
votes
0answers
52 views

Numerical Analisys and StepDataPlot

I'm using StepDataPlot to compare several methods for differential equations. Does exists a function, or something else, to find the number of steps that the choosen method used to find the numerical ...
2
votes
1answer
59 views

WhenEvent stops working after first instance

I'm modelling a very simple physical situation is which an object is rested on two moving fingers. Sometimes the object moves with one finger while sliding over the other, while at other critical ...
2
votes
2answers
446 views

Plot Lorenz system

I solved the Lorenz system by using Euler forward method (without using NDSolve). But I am not getting the attractor. The Mathematica code is as follows ...
2
votes
2answers
115 views

Solving coupled ODEs with NDSolve to fit experimental data

I need to fit a multi-exponential data (Intensity x Time) using a model consisting of three differential equations. I want to find the parameters that gives the best fit to the experimental data. ...
0
votes
2answers
93 views

NDsolve complicated function

I'm trying to solve a complicated second-order ODE with NDSolve. I've never used NDSolve before. I've looked a lot of forums and tried some things, but I haven't been able to get the ODE's solution. ...
2
votes
1answer
85 views

Problems with multidimensional system of ODEs

I am trying to look at the migration of "i" number of species "c" in "10" number of habitats {designated as "j"} and to study their population size as a function of time "t". I have this following ...
0
votes
1answer
186 views

NDSolve::ndode: Input is not an ordinary differential equation [closed]

I am new to Mathematica. I am working on solving the following different equations numerically written in the code as below. ...
1
vote
1answer
123 views

DSolve gives no output

I have troubles finding a solution to a system of three coupled nonlinear ODEs. When I put it into Mathematica, I get back the input as an answer. Could anyone tell me what I'm doing wrong? Here is ...
1
vote
1answer
106 views

Singularity problem of a 2nd order differential equation

I would greatly appreciate your help in implementation of Mathematica for solving a 2nd order differential equation expressing some important engineering problem. Apparently, this equation has no ...
5
votes
3answers
181 views

How to change symbols in differential equation with a single rule?

Problem Suppose I have a differential equation such as $\qquad f'(x)+f(x)=0$ and I want to change it into $\qquad y'+y=0$ My Method Using ...
2
votes
1answer
288 views

Heat transportation equation

I have a problem with the solution of the heat transportation partial differential equation in cylindric coordinates. Basically I have to numerically solve the equation for a pipe through wich the ...
2
votes
1answer
80 views

how to write generic equation for Recurring differential equations?

Hi I am a biologist and I want to model some ecological data that I have. I am new to mathematics and to ODEs. I want to write generic equations for a multi-dimensional system of ODEs. So, I want to ...
0
votes
1answer
109 views

Problem in solving a simple Laplace equation

I am trying to solve the following Laplace PDE in MMA: $$\frac{\partial^2 T}{\partial x^2}+\frac{\partial^2 T}{\partial z^2}=0$$ subject to the boundary conditions: $$\frac{\partial T}{\partial ...
3
votes
0answers
78 views

Diagonalisation of equations for NDSolve

I have a linear matrix differential equation and I wish to speed up evaluation by diagonalising using eigenvectors. There is an example in Help for finite elements under "swinging beam" that is ...
0
votes
1answer
106 views

Solving of three non-linear simultaneous differential equations with given boundary conditions

I am trying to solve three simultaneous differential equations in Mathematica-10 but I am not able to get the solutions. After running the following command as I am pressing shift+enter it just simply ...
1
vote
0answers
127 views

How to write code for solving a second order differential equation? [closed]

I am new to Mathematica and am trying to figure out how to solve the following second order partial differential equation using DSolve. $\qquad U C_{x}+V C_y= ...
1
vote
1answer
337 views

How can I use Mathematica to solve a Stefan Problem using an explicit scheme?

I would like to plot the temperature distribution for a particular case. the problem is stated in the paper, behind a paywall here, summarized as Consider a one-dimensional container of length l, ...
0
votes
1answer
49 views

Checking the solution of a differential equation with a boundary condition depending on an arbitrary function

I have the partial differential equation: $\qquad U_{x} - 4 x^{2} U_{t} = x U, \qquad U(x,0)=f(x), \qquad x \in (- \infty, \infty), \qquad t \in (0, \infty)$ Where $U_{x} = \frac{\partial ...
1
vote
1answer
137 views

Finding equilibria to a system of 3 ODEs with 11 unknown parameters. Looking for the intersection of 3 surfaces

I have the following system of 3 ODEs of 3 variables $(\ell,M,h)$ and 11 parameters $(\sigma_{\ell},\mu_{\ell},d_{\ell},\sigma_M,\alpha_1,\beta,\alpha_2,\nu_M,\sigma_h,\nu_h,d_h)$: ...
0
votes
2answers
125 views

Why does Mathematica Hold my DSolve?

In one cell, I have ...
7
votes
1answer
197 views

ODE w/seasonal forcing term

I am working my way through a mathematical modeling book, and I'm having trouble replicating one of the results. The Differential equation is given as: $\frac{dC}{dt} = \frac{F}{V}(C_{in}-C)$, where ...
0
votes
1answer
112 views

How to specify a NeumannValue in a system of non-linear partial differential equations?

I am trying to solve a nonlinear system of partial differential equations. If I assume DirichletConditions it all works well. ...
1
vote
1answer
197 views

Differential equation solution

DSolve[y''[x] + (a - (b*x^2 - c)*x^2)*y[x] == 0, y[x], x] I couldn't solve this equation, please help