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

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0
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14 views

Problem in computing Dsolve

I want to compute my result using Dsolve. The code is given below. ...
0
votes
0answers
14 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 ...
0
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0answers
44 views

Problems with NDSolve [on hold]

I have the following code. ...
0
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0answers
54 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 ...
0
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0answers
28 views

NDSolve for solving rate [on hold]

I tried to evaluate this code ...
0
votes
2answers
69 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
vote
1answer
64 views

Solve system of equations with implicit function

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 $f$ ...
10
votes
1answer
598 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
45 views

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

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
62 views

Inverse Laplace Transform difficulty

I am asked to find the inverse Laplace transform of: $$F(s)=\frac{2s^2+s+13}{(s-1)((s+1)^2+4)}$$ I did the partial fraction decomposition by hand and got: $$F(s)=\frac{2}{s-1}-\frac{3}{(s+1)^2+4}$$ ...
0
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1answer
80 views

Solving differential equation with initial conditions

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

Laplace equation

I tried to run this code, but it doesn't work for NDSolve ...
1
vote
2answers
187 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: ...
0
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0answers
16 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
30 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
75 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. ...
5
votes
1answer
108 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
17 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
47 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
82 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
51 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
131 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
46 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. ...
-2
votes
0answers
31 views

Difference between DSolve and NDSolve [closed]

What's the difference between DSolve and NDSolve? I know both can be used but I'm not sure of the exact difference.
1
vote
1answer
73 views

Constants from differential equations

I have a problem, I've solved 2 diff equations and I have: ...
1
vote
3answers
94 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
115 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
70 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] ...
3
votes
1answer
127 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
36 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 ...
3
votes
0answers
60 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
vote
1answer
96 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
votes
0answers
30 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
78 views

Creating a nonlinear phase portrait

I am putting all of my code in one block for easy copy and paste. ...
0
votes
1answer
44 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
votes
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: ...
1
vote
1answer
46 views

A With and ContourPlot difficulty

Consider: sys = {u (1 - u + a v), r v (1 - v + b u)}; With[{a = 2, b = 3, r = 1}, Evaluate[Thread[sys == {0, 0}]]] Which gives the output: ...
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0answers
34 views

Axes in a vector plot

Consider: ...
0
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1answer
42 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=0.4p(1 - p/30), 0 <= t < 5 and 0.4p(1 - p/30) - 0.25p, t > 5
1
vote
2answers
143 views

How can I create function which contains an ODE system and its numeric solution?

I have created a function like the following, which contains an ODE system. And I want to know the effect of different parameters. ...
1
vote
1answer
41 views

Plotting 2nd order ODE solution for specific values of constants

Suppose that I have a 2nd order, linear ODE and I want to plot the solution I found using DSolve. How can I plot giving specific values of ...
0
votes
1answer
38 views

Problems with DSolve [closed]

I'm trying to solve and plot a second order ODE. Here is my code: DSolve[y''[x] + 4 y'[x] + 12 y[x] == 80 Sin[2 x], y[x], x] Problem 1... it sticks me with a ...
0
votes
1answer
59 views

Plot an ODE solution for a list of specific constants [closed]

Let's say I have a 1st order ODE and want to plot the solution. What I have been doing until now is: ...
6
votes
2answers
169 views

Plotting separatrices for nonlinear system

Consider the system: \begin{align*} x'&=(1-x-y)x\\ y'&=(4-7x-3y)y \end{align*} The system has a saddle point at (1/4,3/4). How can I plot the separatrices on the phase portrait having domain ...
5
votes
2answers
121 views

Kernel quits without error in NDSolveValue

I am using the latest 10.1. The following single line command makes the kernel quit without error message (just a beep): ...
16
votes
1answer
430 views

Analogue for Maple's dchange - change of variables in differential expressions

Maple owns an interesting function called dchange which can change the variables of differential equations, but there seems to be no such function in Mathematica. ...
1
vote
1answer
59 views

Error with using NDSolve [duplicate]

I am currently trying to numerically solve a system of differential equations. Here is my code: ...
0
votes
1answer
28 views

Boundary condition not correctly imposed for NDSolve

I notice that when plotting the below NDSolveValue ...
1
vote
0answers
49 views

Failing to solve a simple PDE with NDSolve

I'm trying to solve the following PDE. Actually this is a major simplification of the original with all x,z dependent coefficients being fixed. For some reason Mathematica (10.0) cannot solve even ...