8 votes
Accepted

Error in Attempting Moving Boundary Fluid System

… why would the system be classified by NDSolveValue a differential-algebric system, since every variable has at least one differential term? This isn't quite ...
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  • 52.4k
7 votes

How do I plot the Lorenz attractor inside an ellipsoid?

Unless I've done something wrong, it does not appear that the trajectories stay inside the given ellipsoid. The given ellipsoid can be rewritten as $$ \frac{P}{b} x^2 + \frac{1}{b} y^2 + \left( z - \...
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6 votes

Solution on nonlinear pde with intial condtion

It produces an error. You need boundary conditions. You only have initial conditions. For numerical solver, both are needed. I put some below, but you need to put the correct ones as you know the ...
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  • 109k
5 votes
Accepted

Symbolic solution for steady-state heat equation i.e. Laplace equation inside cylinder

This post contains several code blocks, you can copy them easily with the help of functions here. It's not too surprising to see DSolve failing on the problem, ...
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  • 52.4k
4 votes

Ploting solution to a differential equation with different parameters

Something to get you started,. You can use Manipulate ...
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  • 109k
3 votes
Accepted

Problem with a DAE and DiscreteVariables (II)

It's well known that DAE solver of NDSolve is generally weaker than its ODE solver. (We should admit DAE solving is generally hard than ODE solving, of course. ) So,...
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  • 52.4k
3 votes

Solution on nonlinear pde with intial condtion

There are initial values missing. For an example I assume the following initial values: U[0, t] == 1.4, V[0, t] == 2 Then there should be a comma instead of a ...
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  • 24.8k
2 votes

non-linear first ODE with boundary condition

This is the same idea as Nasser's, but my route yielded solutions in a slightly different form. ...
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  • 216k
2 votes

non-linear first ODE with boundary condition

Here is my hand solution with the help of the computer Solve \begin{gather*} \boxed{\frac{\left(y^{\prime}\right)^{2}}{y^{2}}-\frac{b y^{\prime}}{y}-\frac{k}{3 y^{2}}-\frac{f}{3}=0} \end{gather*} With ...
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  • 109k
2 votes

why DSolve gives "Warning: one or more assumptions evaluated to False." when I am not using any assumptions in the call?

It looks like one of the internal steps of DSolve is running ...
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  • 21
2 votes
Accepted

Linear ODEs with NDSolve

I have a package for solving eigenvalue boundary value problems using the Compound Matrix Method with the Evans function, which I'll use here. The package is available on my GitHub (which has a ...
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  • 5,438
2 votes

Heat Equation with Mobile Boundary

Since OP is having difficulty in understanding previous related posts, I'll solve the problem as a favor. But I won't explain much because there's nothing new in this problem compared with previous ...
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  • 52.4k
2 votes

Problem with a DAE and DiscreteVariables

One can keep differentiating until the DAE turns into an ODE: ...
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  • 216k

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