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

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75 views

Using Mathematica to solve a recursive system of differential equations

I believe I have a difficult problem to work on specially because I don't have any previously experience using Mathematica in this kind of situation. So I'll try to describe it as best as I can hoping ...
0
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0answers
26 views

Coupled Mass Transport in two media using NDSolve

I'm trying to model simple 1-D diffusion in two media with different diffusivities. It's a transient problem so I have a PDE. I have concentration everywhere = 0 at time t=0, and suddenly at t>0, I ...
0
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1answer
43 views

Having trouble interpreting the results DSolve gives for the Laguerre equation

I am trying to solve a second order ODE using Mathematica. Before I get into solving my (more complicated) problem, I am trying to use DSolve on known ODEs to check that the answer that Mathematica ...
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0answers
33 views

How to use a While loop with NDSolve?

So basically I have this coupled ODE system I'm trying to solve numerically: ...
1
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0answers
30 views

NDSolve with external function

I have a complicated function g[a_,s_,t_] where s_and t_ are constants added by hand for ...
1
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2answers
212 views

How to Fit experimental data with 4D ParametricNDSolve?

Let me first explain the background problem. I'm trying to solve a problem with a projectile motion in 4D such that the position vector is: $\boldsymbol{r}(t)=\boldsymbol{r}[x(t),y(t),z(t)]$ I have ...
1
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1answer
145 views

Solution of a system of differential equations with a correction factor varying over time

Dear Mathematica users, I am trying to solve a system of equations of first order and time depedent. The system has 5 equations, one for every variable which varies over time. At the moment I am ...
0
votes
1answer
47 views

simple dynamical system with disturbance

I am new here and trying to simulate a very simple dynamical system with periodic force or Dirac function: $$mx'' + bx' + kx = u(t)$$ I want to draw the displacement(position) and velocity of the ...
0
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1answer
71 views

Why does DSolve not give the expected analytical solution for a system of DAE? [closed]

I made a mistake in typo I am trying to solve the following system of DAE: X'[t] - y*Y[t] + x*X[t] == 0 Z'[t] - y*Y[t] + x*Z[t] == 0 X[t] + Y[t] + Z[t] == 1 with ...
2
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0answers
105 views

Problem solving a nonlinear partial differential diffusion equation [closed]

EDIT: actualy the nonlinear partial differential equations for interacting density distributions, including boundary conditions, should be given as $$ \frac{\partial\phi}{\partial t} = D ...
0
votes
1answer
87 views

How to compute DSolve or NDSolve for kind of piece wise function?

I need to Compute the expression for two functions. q[t] and q1[t] over certain range of time. The code is given below. ...
0
votes
1answer
54 views

Solving a system of ode and plotting the nullclines

I have the following problem to solve it is a system of two ode's. I'm given that q=2/Sqrt[1 + 1600 y] and then the ode's are as follows. ...
1
vote
2answers
105 views

Minimize the sum-of-squares errors for a system of ODEs

I'm trying to minimizing the sum of squared errors on a 2-equation system of ODEs and empirical data. I keep getting an error and I think the root of the problem is my invocation of ...
0
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0answers
58 views

System of non linear differential equations with two unknowns

I am new to Mathematica and am trying to solve a system of 3 (non-linear) equations with two variables $x,\ y$ and one unknown function $f(x,y)$ of these two variables. The third equation defines the ...
1
vote
1answer
122 views

Why DSolve[] does not work?

I try to find the analytical solution to the ordinary differential equations as fellow: $$\frac{d^2 \theta}{d t^2} = \dfrac{-M\cos\theta\sin\theta(\frac{d\theta}{dt})^2 - ...
0
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1answer
61 views

Problem in computing Dsolve

I want to compute my result using Dsolve. The code is given below. ...
0
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0answers
150 views

fourier frequency analysis for NDSolve of complex variable

i have a set of coupled equations for complex amplitudes c1 and c2, for which i'd like to find frequency and phases (and phase shift); i looked up for some nswers on the forum, but can't seem to find ...
1
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0answers
91 views

Black Scholes PDE solved by method of lines

I've been trying to solve the Black Scholes partial differential equation (BSPDE) by transforming it to the heat equation (HE) form and using method of lines (discretizing spatial argument and leaving ...
1
vote
2answers
101 views

differential equation of order2

I want to solve the following differential equation ode = x*y''[x] + y'[x] + 4*x^2*(x^2 - 1) y[x] == 0 But do not know how to actually solve it. Any suggestion?
1
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1answer
85 views

Solve system of equations with implicit function [closed]

I am trying to solve a system of 3 (non-linear) equations with two variables $x,\ y$ and one unknown function $f(x,y)$ of these two variables. Also, the system includes the change of this function $f$ ...
14
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1answer
797 views

Solving and Animating Three Body Problem

I am attempting to solve a three-body problem using the Lagrange formalism, with a 1/r potential. I started off by defining T and U (kinetic and potential energy) as follows: ...
0
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1answer
47 views

Solve system of differential equations and show the chaotic behavior of the solutions [closed]

I want to solve a system of differential equations and show the chaotic behavior of the solutions. Here x[t], y[t] and ...
0
votes
1answer
135 views

Solving differential equation with initial conditions

I want to solve the following differential equation with initial conditions: ...
-1
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1answer
95 views

Laplace equation

I tried to run this code, but it doesn't work for NDSolve ...
1
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2answers
196 views

How to solve for “k”

So the question is given that the atmospheric pressure is modelled by the differential equation p'[h]=-kp[h], p[0]=1013, p[20]=50. find k and comstant of integration. My code was: ...
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0answers
23 views

ImplicitRegion Error in NDSolve?

I'd like to solve a differential equation with some initial conditions to get an eclipse curve for Earth's orbit using Newton's Law in a cylindrical coordinate. NDSolve gave me two more useless ...
0
votes
2answers
32 views

solving ode and plotting solution vs time

I'm currently trying to solve this system of two ode's and can't seem to be able to solve them. I am new to coding, so I don't know where I could have done a mistake. I'm attaching the code which I ...
0
votes
1answer
82 views

My simulation is not never finishing and it is taking so much time?

I am running simple code which involves calculation of two first order differential equations.It is taking so much time and i am unable to get the results as the simulation is never finishing. ...
7
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1answer
136 views

Difficulty in getting correct Gaussian curve for diffusion of point source

I want to solve diffusion of a point source numerically and check it against analytical solution. first I define initial profile, ...
0
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0answers
21 views

How to solve coupled first-order ODE with vectors?

m * v'[t] = q * (E + v x B) using the following: B = (0,0,B0), E=(Eperp,0,Ez). How would I find the general solution of ...
0
votes
1answer
53 views

DSolve not outputting any result

I'm trying to solve a system of differential equations using DSolve, but I am not getting any output beyond a repetition of my input: ...
-1
votes
2answers
90 views

How to make sure input is an ODE

I'm having trouble wrapping my head around why this isn't an ordinary differential equation. ...
0
votes
1answer
126 views

How To Use D[ ] to Define a System of PDEs

We have two variables $u_{1}$ and $u_{2}$ which are functions of $x,t$. That is, $u_{1}=u_{1}(x,t)$ and $u_{2}=u_{2}(x,t)$. Consider the the system of partial differential equations $$\frac{\partial ...
5
votes
1answer
160 views

How to plot the solution of a Partial Differential Equation?

My attempt. I need to solve numerically the Complex Ginzburg-Laudau Equation (CGLE): $$ \frac{\partial A}{\partial t}=\epsilon A-(1+i\beta)|A|^2A+(1+i\alpha)\nabla^2A $$ I'm using a uniform initial ...
0
votes
1answer
65 views

How to properly use conditionals inside NDSolve

Currently I am working with Mathematica to learn the program, and I'm confused what exactly is wrong with this code. ...
1
vote
1answer
77 views

Constants from differential equations

I have a problem, I've solved 2 diff equations and I have: ...
2
votes
3answers
119 views

DSolve with assumptions

I'm new to mathematica and was wondering if someone could help me. I have a differential equation which is: $\frac{dy}{dx} = 1/2 y(1 - y)(a - y + a y)$ It has initial condition $y(0) = y0$ and ...
4
votes
3answers
176 views

How to fit parameters in a system of coupled differential equations

Problem description: I'm studying a chemical reaction that can be modeled by a system of coupled differential equations, and I want to use measured data to determine the parameters that appear in the ...
1
vote
3answers
82 views

NDSolve parametric plot

Here is my code. s = NDSolve[{f'''[x] + f[x]*f''[x] == 0, f[0] == A, f'[0] == 0, f'[10] == 1}, f, x] I want to plot f''[0] ...
5
votes
1answer
220 views

Numerical solution of IVP for linear ODE with variable coefficient runs wild soon

Cross posted in scicomp.SE. A friend of mine showed me this initial value problem (IVP) for a linear ordinary differential equation (ODE) with variable coefficient: $$y''(x)=\left(x^2-1\right) ...
4
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0answers
39 views

Strange behaviour of suggestion bar to solve an ODE, potential bug

InputE^(-(1/2) x[t]^2) (Derivative[1][x][t]^2 - (x^\[Prime]\[Prime])[t]) == 0and evaluate, then press the solve ode button on the suggestion bar. It will return ...
7
votes
1answer
260 views

Diverging solution to coupled second order ODEs from NDSolve

For a physics application I am considering the radial Bogoliubov-de Gennes equations in two dimensions. In dimensionless form they read as follows $$ \begin{cases} ...
1
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1answer
109 views

How to combine VectorPlot and Plot3D

I have a problem with VectorPlot and Plot3D, and I have a code for both but I dont know how to plot the same figure. Here is the code for Plot3D: ...
0
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0answers
43 views

How to solve a second order non-linear differential equation analytically?

I have the thermoelectric second order non-linear differential equation: Can some one please help me solve this equation. I need to solve for $T$. The two boundary conditions for $T$ are: $\quad ...
2
votes
0answers
91 views

Creating a nonlinear phase portrait

I am putting all of my code in one block for easy copy and paste. ...
0
votes
1answer
47 views

How to obtain coefficients after solving differential equation of order 2 with initial condition?

I have the following answer of a differential equation of order two ...
0
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0answers
34 views

Strange difficulty with DSolveValue

Consider: sys = {u (1 - u + a v), r v (1 - v + b u)} (* {u (1 - u + a v), r (1 + b u - v) v} *) And: ...
2
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0answers
37 views

Axes in a vector plot

Consider: ...
2
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1answer
111 views

How I can make the StreamPlot of this differential equation?

I need the StreamPlot of this differential equation but I don't know how. dp/dt = 0.4 p(1 - p/30), 0 <= t < 5 and 0.4 p (1 - p/30) - 0.25 p, t > 5