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

3 votes
1 answer
1k views

How to directly input calculated Geodesic differential equation into *NDSolve*

I am trying to find the trajectory of a test particle around a relativistic object. Initially, I was trying the Kerr metric as spacetime but the final simulations clearly were not correct as I saw the …
diffusiondiver11's user avatar
3 votes
1 answer
156 views

Not able to reproduce the result of this paper to test if a system is chaotic or nonchaotic

I am trying to reproduce the results of a paper A new test for chaos in deterministic systems by Georg A. Gottwald and Ian Melbourne. This paper talks of a simple 1-0 method to determine whether a dyn …
diffusiondiver11's user avatar
2 votes
3 answers
99 views

How to plot $\left|y(t)\right|'$ where $y(t)$ is the output from NDSolveValue

I have a complex valued ODE. ysol = NDSolveValue[{y'[x] == I Sin[y[x] Cos[x y[x]]], y[0] == .5}, y, {x, 0, 30}]; Plot[Abs[ysol[x]], {x, 0, 30}, PlotRange -> All] The function $\left|y(t)\right|$ is …
diffusiondiver11's user avatar
1 vote
Accepted

Mathematica is considering $\theta$ as an independent but it is not independent

For those equations which were already there and for also ones added in the post script, the mistake is in the syntax. posted code aa = x[s] Cos[y'[s] z[s]] + t''[s]; bb = Sin[x'[s]] Cos[y[s]] + t[s …
diffusiondiver11's user avatar
0 votes
1 answer
102 views

Mathematica is considering $\theta$ as an independent but it is not independent [closed]

ADDED LATER: READ THE POST SCRIPT TEXT AT THE END Before saying anything else I would like to say please don't edit my codes in this question. I know that they are not formatted properly but they'll …
diffusiondiver11's user avatar
0 votes
1 answer
50 views

Why is Mathematica not simplifying further even after providing assumptions?

m = {{0, 0, 1, 0}, {0, 0, 0, 1}, {-5 X^2, X^2, 0, 0}, {X^2, -X^2, 0, 0}}; Simplify[Eigenvalues[m], Assumptions -> X>0] The output I get is this below. The last two eigenvalues are not in their simple …
diffusiondiver11's user avatar