# Tag Info

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• 121k
1 vote
Accepted

### 3D Parametric Plotting for N Charged Particles in a Nonuniform Electric Field

Your initial conditions are lists with 1 element, but numbers are expected. E.g. instead of x1[j][0] == pos0[[j, 1, ]] write x1[j][0] == pos0[[j, 1, 1]]
• 24.9k
Accepted

• 13.6k

### 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 ...
• 5,433

### 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 ...
• 21
Accepted

### NDEigensystem: 1D problem with discontinuous coefficients

Yes, it's possible, we just need to use the documented but seldom-used and (probably) confusing last syntax of NDEigensystem. As discussed in Position of ...
• 52.6k

### Solve singular fourth order ODE

This is an incomplete answer, but perhaps you can combine it with the answer of @MichaelSeifert. It is more manual in a way, but perhaps allows you to understand where the numerical issues come from. ...
• 743

### How to solve 2D Heat equation on rectangle with NDSolve?

The code is not working, what is my mistake? You had two minor mistakes. Your Rectangle was wrong Rectangle[{0, a}, {0, b}]. ...
• 110k

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• 13.6k
Accepted

### Linear ODEs with NDSolve

This eigenvalue problem can be solved largely symbolically as follows. With the equations rationalized, ...
• 58.4k

### Linear ODEs with NDSolve

Update As mentioned by bbgodfrey and by Michael E2, the code I had proposed below only returns a trivial constant solution, as the following indicates: ...
• 60.4k

### Solving this system of differential equation with NDSolve

I fixed the exp that @cvgmt noted, pulled τc and Ip out of ...
• 17.7k

### How to Plot the solution of the heat equation on rectangle

u[x, y, t, 5, 5] is too small when t is large. Here we set {t, 0, 2}. Replace ...
• 33k

### How to Plot the solution of the heat equation on rectangle

A few observations. It is generally better to use a fixed PlotRange rather than All for an animation so your scale is not ...
• 7,419
Accepted

### Why does NDSolve[] want to treat my equations as Delay Differential Equations?

Nice to have the ODEs and ICs separate, because it makes separate analyses easier: ...
• 216k

### Why do two different Mathematica files with the same ODEs substituted with the same values give me different outputs?

The problem was that the numerical data values should be put right before the NDSolve command execution (not earlier)-then it can handle this really well. I dont know why it is such a difference for ...
• 47
Accepted

### Problem with a DAE and DiscreteVariables

As stated in the question, a[t] does not behave properly for the code in the question, which probably is a bug. Circumventing this problem can be accomplished with <...
• 58.4k
Accepted

### NDSolve for Laplace equation on disk is not working

3 issues here. You've mixed up polar coordinates and Cartesian coordinates. Since the equation is defined in polar coordinates, the shape of domain of definition is no longer a ...
• 52.6k
1 vote

### How to define a function of parameters of a DSolve output?

An other way with DSolve is ...
• 15.7k
1 vote

### How to define a function of parameters of a DSolve output?

You can solve with the parameters directly: ...
• 216k

### NDSolve for Laplace equation on disk is not working

It looks like the problem was with the periodic BC and JM's above showed how to handle this periodic BC. This below shows that DSolve can also solve this ...
• 110k
Accepted

### How to shoot backwards using the "Shooting Method"?

The "StartingInitialConditions" suboption sets the IC at x == 0.9, and with good values for the IC, a successful ...
• 216k
1 vote

### Plot3D in Mathematica a function

Another approach: G[s_, t_] = Min[s, t] (Max[s, t] - 1); Plot3D[G[s, t], {s, 0, 1}, {t, 0, 1}, PlotStyle -> Green]
• 13.6k

### Phase Portrait on a Simplex

Here's another way (equations pulled from docs -- it's easier): ...
• 216k

Let k -> -kk ...
• 15.7k

### The solution for Sinh[] and Cosh[]

If we multiply the arbitrary constant C[1] by I, FullSimplify can do the job if passed the ...
• 33k
Accepted

### Phase Portrait on a Simplex

Look what I got. Do not rush to accept the answer, look more carefully. You may need to add the equation of the simplex you are writing about to the plot for additional visualization. I can't help you ...
• 1,721

### How to put 2 or 3 NeumannValue conditions?

NeumannValue type boundary conditions may overlap, while DirichletCondition may not overlap. So something like this: ...
• 36.1k
1 vote

### Why do I see Part::partw error when using NDSolveValue?

This was a bug that's fixed in V13.0 (or earlier).
• 36.1k
Accepted

### How does FindRoot decide if a solution has converged?

Turning my comment into an answer. I am in a rush now, Here are the relevant literature references for the affine covariant Newton solver that is implemented as a method of ...
• 36.1k
1 vote

### If or Piecewise dependent coefficients in NDSolveValue

There are examples in the documentation that show how to do this: Have a look at the nonlinear (single material) model on the HeatTransferPDEComponent ref page. Concerning multi-materials you could ...
• 36.1k

### Inactive form for PDE and symmetry

Up until version 13.0 the finite element method works with Cartesian coordinates. In 13.1 one can use a truncated cylindrical coordinate for axisymmetric PDEs. It's unlikely that something else will ...
• 36.1k
Accepted

### NDEigensystem returns reversed list of eigenfuctions

As I pointed out in a comment above, this is because of an issue described in the documentation: Ordering of dependent variables. The simplest way to deal with this is to specify the "...
• 36.1k

### Plot3D in Mathematica a function

Option 1 is as follows: ...
• 177

...
• 1,721
Accepted

### Plot3D in Mathematica a function

Try this: T[s_, t_] := Piecewise[{{s (1 - t), 0 <= s <= t <= 1}, {t (1 - s), 0 <= t <= s <= 1}}] Plot3D[T[s, t], {t, 0, 1}, {s, 0, 1}] ...
• 35.1k