Tagged Questions

2
votes
0answers
74 views

Conditional statements in intial conditions?

This is potentially a daft question, but I thought I'd ask it; I have some material free to diffuse in a boundary between rn and ro; I've been able to get it working nicely for neumann type boundary ...
0
votes
1answer
122 views

solution of differential equation

I have the following code that gives you a phase portrait of a 2d system and I can't understand what means the 3rd and 4th line (sol1 and sol2). ...
0
votes
0answers
51 views

DSolve::overdet for system of linear PDEs

I would like to resolve symbolically the following equation: ...
3
votes
1answer
172 views

Create Euler equation

I've tried to make some research, but without any luck. How do I setup the Euler equation for this in Mathematica?: $ \text{Min} \int_0^1\left(2x^2+ \left(4t-5 e^{r \, t} \right) x \, \dot{x} + ...
2
votes
0answers
89 views

differential equations with implicit functions

I have an ordinary differential equation that contains coefficient functions that depend implicitly on the independent variable via an algebraic equation. I am trying to go ahead and use NSolve to ...
0
votes
1answer
187 views

DSolve fails to solve second order PDE

I have a very simple example of a second order PDE: eqn = D[u[x, y], x, y] + u[x, y] == 0; sol = DSolve[eqn, u, {x, y}] and Mathematica cannot solve it! What is ...
4
votes
1answer
177 views

NDSolve does not respond

For some sets of constants, NDSolve gives me true solutions, but when I try for example, T = 1/(2*2200), Mathematica does not respond. What can I do? The code below ...
0
votes
1answer
99 views

Solving a differential equation for a variable in a function

This may sound like a very trivial question, but I need to solve a differential equation as follows: ...
4
votes
2answers
516 views

Solving a time-dependent Schroedinger equation

I want to solve the time-dependent Schroedinger equation: $$ i\partial_t \psi(t) = H(t)\psi(t) $$ for matrix, time-dependent $H(t)$ and vector $\psi$. What is an efficient way of doing this so ...
0
votes
1answer
71 views

Evaluating derivatives for use in solve

I need to evaluate the derivative of a function. My function looks like approx[vector_, x_] := Sum[vector[[n]]*Basis[n - 1, x], {n, 1, Length[vector]}] and I'm ...
1
vote
0answers
121 views

NDSolve equations contain solution from solving cubic equations

I'm having trouble using NDSolve to solve equations that were obtained from solving cubic equations. In my problem, I first obtained 6 functions (ca1, ...
1
vote
1answer
96 views

Finding parameters for first positive root of solution to differential equation to be equal to a desired value

I have a differential equation with parameters. The objective is to vary the parameters such that the first positive root of the solution is equal to a desired value ...
3
votes
0answers
69 views

Symbolic solution to ODE, pure InverseFunction not evaluated

I'm new to Mathematica and I don't understand why in the solution of the following ODE, the #1 in the pure function is not immediately replaced by the corresponding ...
-3
votes
1answer
378 views

How can Mathematica solve this set of differential equations? [closed]

I'm trying to solve this set of non linear differential equations, but apparently it won't solve. I really tried all the tweaks I could think of. Still no progress... So now I turn to you, can you ...
0
votes
1answer
338 views

How can I understand the result Mathematica returns from DSolve?

I have solved an ODE using DSolve, but I have a problem with understanding the solution. In general the solution is in the form: ...
3
votes
1answer
246 views

Eliminating functions from system of PDE in Mathematica

Mathematica users, Let's see an example of three PDEs: How can I eliminate variables q1[x,y,z] and q2[x,y,z] from a system of ...
3
votes
1answer
478 views

NDSolve with vectors

I'm stumped. I'm trying to write this using vectors, but the 2nd derivative isn't being expanded like I expected it to be. This is a system of equations for a projectile with quadratic drag and ...
2
votes
1answer
206 views

Vector Analysis: Why are the Grad, Laplacian and Div being evaluated to zero

For the non linear partial differential equation below, why are the Gradient, Laplacian and Divergence being evaluated to zero despite using the VectorAnalysis ...
3
votes
1answer
396 views

Finding the Minimum value of an interpolating function

I can't seem to use FindMinValue to find the min. value of a curve represented by an interpolating function. For instance the below code generates an interpolating ...
1
vote
2answers
206 views

Replacing variable in an equation with an Interpolating function polynomial and plotting residual

I was trying to plot the residual for the solution of my PDE. However, I was unsure about a couple of things. I imported the data and created an Interpolation polynomial with ...
2
votes
1answer
306 views

Inconsistent initial and boundary conditions

I have a 4th order nonlinear PDE with the following BCs and IC: ...
0
votes
1answer
396 views

how to solve an implicit integral equation? (iterate to a functional fixed point?) [closed]

I reduced a (special case) of my problem to the following code. Even though in this special case all related functions are analytical, DSolve is not the tool for this, though I am indeed looking for a ...
6
votes
2answers
333 views

Very long Refine/Solve batch run - is my code broken, or just complicated?

So I'm trying to run some Mathematica code in batch mode from my university cluster. Specifically, I'm trying to find the equilibria of a system of ordinary differential equations. Inspired by the ...