Tagged Questions

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

138 views

How to solve time dependent coupled differential equations? [closed]

I am trying to solve time dependent coupled differential equations with know initial conditions. I am just a beginner in terms of coding so would really appreciate if someone can give me an example of ...
132 views

Getting the message NDSolve::underdet:

I am solving the wave equation with initial position and velocity function: ...
71 views

NDSolve does not satisfy initial conditions

For the problem I'm facing, I have three coupled diff eqns that I'm trying to solve ...
261 views

How to solve a pair of coupled 2nd order equations using shooting method

I have a pair of equations for x[t] and y[t]. Both are 2nd order and they are coupled. Now say that I know the following ...
41 views

Boundary condition [duplicate]

I'm having the following issue that can not find a solution , by using this boundary condition v[0, t] == u[1, t] that Mathematica does not understand, someone ...
201 views

Improving NDSolve computation speed for 3D stationary PDE

Continuing my last question, I am trying to solve 3D Schrodinger equation (with mass equals to 1) and with no potential (I will add a potential later). The analytical solution for this equation is ...
148 views

Equal flow boundary conditions

I'm having the following issue that can not find a solution , by using this boundary condition v[0, t] == u[1, t] that Mathematica does not understand, someone ...
246 views

Extending NDSolve beyond a singularity

The $\tan$ function satisfies the following IVP: $$y'=1+y^2 ,\quad y(0)=0$$ and has simple poles at the points $x=\pi/2+ \pi n$ for integer $n$. When trying to get $\tan$ via numerical integration,...
155 views

Convert DE to first order?

I have the following set of second-order differential equations: ...
240 views

How should I deal with messages being produced by my Manipulate?

I have made a knockoff of John Polking's dfield for a web-embedded CDF (via Enterprise Mathematica). My code extends that from Belisarius who last year showed me how to use ...
88 views

Problems with solving two coupled lorenz equation with NDsolve

I have a system of two coupled lorenz equations and I'm to integrate it: ...
51 views

NDSolve error with a given system of equation [closed]

I know that my question will be very similar to NDSolve giving NDSolve::deqn: message when given my system of equations . Sorry for that, I am so new on Mathematica. I have tried to use the ...
161 views

How to speed up NonlinearModelFit applied on a NDSolve solution?

I'm trying to perform fittings of a model defined through a system of ODEs to data consisting of time courses of a measured quantity. As described in a previous question, the system of ODEs is as ...
304 views

NDSolve fixed step problem

Working example here: Drive folder (have both files in the same directory! Notice: the line <<variables' in the file seems to throw an error for me, but ...
92 views

47 views

NDSolve with NIntegrate [duplicate]

I'm new to Mathematica and I'm trying to use it to solve some equation like: NDSolve[x'[t]+NIntegrate[x[tau],{tau,0,t}]==20,x,{t,0,10}] But it keeps giving me ...
73 views

Matrix issue with NDSolve

I am solving a differential matrix equation with NDSolve. ...
123 views

Problem in understanding PDE solution

I solved the PDE shown below and I got the solution. I am new to this tool. In the solution, I have a constant multiplied by a vector like function (please refer second term of the solution). What ...
73 views

Trouble solving a system of partial differential equations [closed]

I am trying to solve a system of linear PDEs analytically and I dont get the answer. I am new to this tool, appreciate your help ...
95 views

Solving algebraic looping problem by introducing a unit delay

First, here is my code. ...
54 views

Transform a vector DE into a set of scalar DEs [closed]

I have the vector equality: {{a,b},{c,d}}.D[{x1[t],x2[t]},t]=={{e,f},{g,h}}.{u1[t],u2[t]} I want to solve this using DSolve. ...
481 views

Dipolar magnetic field lines inside a cylinder

I'm drawing the magnetic field lines of a rotating dipole (magnetic field distorded by emission of radiation). Currently, my Mathematica 7.0 code is fully working, but I'm having a constraint which I ...
98 views

In a PDE solution let us integrate out one of two coordinates

Here is a trapezoid within which I am solving a simple Laplace equation with the Dirichlet boundary conditions set at its top and bottom: ...
134 views

The length of the derivative operator Derivative[0,0,2,0] in \ f^(0,0,2,0)[x,y,z,t] is not the same as the number of arguments. >>

I'm trying to solve Maxwell's wave equation but am faced with an error message ...
65 views

Problem with solving coupled differential equations

The following code seem to produce an output that appears to be independent of the parameter "fg". It is possible that the way the code is written might be causing it, but how can one fix this problem....
43 views

Is there a way to pre-calculate a slow animation and then run easily with no lag? [duplicate]

I have an animation of a triple pendulum on a moving base, however even after trying to change the whole coding to make it faster by using module and all it is still pretty bad as I need it to be ...
127 views

code is ignoring WhenEvent

I would like the value of x[t] to be equal to 0 when it has a negative value so I used WhenEvent but it has no effect on my code ...
94 views

Error in the solving of the simultaneous Ordinary Differential Equation [closed]

As I am trying to get the solution of the simultaneous ordinary differential equations ...
244 views

DSolve returns an answer that is not a solution

Investigating DSolve misses a solution of a differential equation, I came across this odd behavior of DSolve. The following DSolve command returns an answer to the ...
88 views

Problem in the solution of the simultaneous Ordinary Differential Equation [closed]

When i am running the following command ...
121 views

How can I write a loop to get many values from a solution?

I am looking at the value of x[t] at day t = 200 over several years. I tried to do it using a For-loop but it didn't work. This ...
336 views

Potential flow over cylinder with FEM: Pressure field is flipped

Much in the fashion of a few problems already answered on Mathematica.SE (1, 2), I am trying to solve the Laplace equation in velocity potential $\phi$ to simulate irrotational, inviscid flow over a ...
186 views

NDSolve : Boundary conditions of lower order

Given the (dummy) problem ...
86 views

how to change parameters in NDSolve? [closed]

I want to solve a PDE with parameters chosen based on the sign of derivative. For instance in the following PDE ...
761 views

Implementing Picard's Iteration for solving ODEs

Picard's Iteration is a way of solving the IVP $$y'(x)=f(x,y(x)), \quad y(x_0)=y_0$$ It consists of defining the following sequence of functions recursively: y_0(x):=y_0 \\ y_{n}(x):=y_0+\int_{...
162 views

How to make the plot smooth

There are some stranges point which cause the figure isn't smooth. I think that the reason is the method of numericial integration. Here is my code, it's pleasure that one can revise the drawbacks in ...
EDIT: I need to solve the following PDE: $\nabla^2\vec{A}=-\mu_{0}\vec{j}$ where $\vec{j}=\sigma\vec{E}$ and $\sigma=1*10^{10}$ which basically boils down to three different PDE's; \$\...