# Tagged Questions

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

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### Saving the result of a NDSolve

I have solved this diff equation (with no problems): ...
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### How to integrate numerically the product of result of NDsolve? [closed]

I am going to integrate the product of the results of NDsolve, in fact If x and y are the results as interpolating function, How I can integrate x*y numerically? <...
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### NonlinearModelFit error: the function value is not a list of real numbers with dimensions {101} at {a,k,m0} = \ {1.,1.,1.} [closed]

So I'm trying to find a sigmoidal fit for my numerical solutions of these two ODEs but I keep getting an error and I don't know how to get around it. Here's my code: ...
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### How to pass arguments in NIntegrate and NDSolve

I am solving PDEs with NDSolve and NIntegrate, but I do not know how to pass arguments correctly. My orignial code is very ...
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### Solving a set of nonlinear equations

I am trying to setup and solve a set of nonlinear equations. I keep getting an error. Here is my problem: ...
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### Find $r$,in terms of variables $U$ and $V$

I want to solve this equation, for $r$: ...
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### Error message when running NDSolveValue

I am trying to solve a set of differential equations but keep getting an error. See message below "NDSolveValue::ndnum: Encountered non-numerical value for a derivative at t=0" The system that I ...
130 views

### NDSolve and differentiation of Abs

I have found several questions about the derivative of Abs and how it is not defined in the complex plane. What I have not found yet is a precise and simple ...
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### How to numerically solve a 1D time-independent Schrödinger equation for two interacting particles

Solving the 1D single-electron time-independent Schrödinger equation has been demonstrated using NDEigensystem here. There, the single-electron Schrödinger equation ...
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### How to plot an Eddington-Finkelstein diagram

I need to plot the same thing as what is shown on the third picture of the site below (sorry, I'm unable to poste that picture here) : http://ion.uwinnipeg.ca/~vincent/4500.6-001/Cosmology/...
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### PolarPlot with InterpolatingFunction not working?

So I have solved a PDE with NDSolve which returns h -> InterpolatingFunction. I can happily plot the results with ...
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### Diffusional equation [closed]

I am still new to Mathematica. I'm trying to solve a diffusional equation ...
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### Can I solve system of differential equation in a matrix form?

I'd like to solve simple system of differential equations: x'[t] == 6x[t] - 6y[t], y'[t] == x[t]-2y[t]; but I want to avoid formulas like DSolve[{x'[t] == 6x[t] - 4y[t], y'[t] == x[t]-2y[t]}, {x,y},...
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### How do I get a 'list' (or something similar) of functions?

I'm solving an NDSolve equation, like: ...
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### How many boundary conditions are required for two coupled Non-linear ODE in two variables?

I'm using NDSolve to solve the following two coupled Nonlinear ODEs in two variables: Equation1 = Equation2 = It can be seen that the level of nonlinearity is very high. I have solved the ...
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### Produce several file outputs within one calculation

I have a differential equation which I solve with NDSolve. With the obtained solution I calculate some quantity. Then a constant in the ODE will be raised (until a ...
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### Looking under the hood of DSolve [closed]

Is it possible to print out information about the algorithms DSolve uses to solve a differential equation? I'm looking for something similiar to this Maple procedure. It lets you specify how much ...
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### Using loops to draw multiple polygons and discretizing them

I am trying to plot the first eigenvalue of the Laplacian operator with zero Dirichlet condition on following figure against decreasing values of $\varepsilon$. I used ...