2.9 Thursday, October 22, 2020

2.9.1 Top new questions this week
2.9.2 Greatest hits from previous weeks
2.9.3 Can you answer these questions?

2.9.1 Top new questions this week

How can I reproduce this mandala with Mathematica?
Tennis Racket theorem
Climbing/Descending the Integer Ladder
Remove inner brackets
Identify the Vertices and Lines around the edges of a free surface - Mesh/DiscreteGraphics
How can I extract the edge points from an image?
How to speed up integers finding function?

How can I reproduce this mandala with Mathematica?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233050

I found this image on the Internet and it is very beautiful. How can I reproduce it? The ideal would be to be able to control the colors of the outside as well as the center.

asked by Susana https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=37778 12 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 32 votes

Tennis Racket theorem

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=232976

Torque-free Euler equations experiment seen in low gravity of Russian spacecraft is modelled here with a view to see its tumbling motion around the intermediate axis \(\omega _2\) rotation. However its ...

asked by Narasimham https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=19067 10 votes

answered by Alex Trounev https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=58388 16 votes

Climbing/Descending the Integer Ladder

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233096

A fun combinatoric puzzle that’s popped up in my work that I think would be cute to have a Mathematica solution to, if anyone wants to give it a go. It’s basically a ladder climbing/descending problem ...

asked by b3m2a1 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=38205 8 votes

answered by Leonid Shifrin https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=81 5 votes

Remove inner brackets

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233206

If I have the result

asked by GlomGive https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=75305 7 votes

answered by wuyudi https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=68689 10 votes

Identify the Vertices and Lines around the edges of a free surface - Mesh/DiscreteGraphics

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=232975

To write a mesher that closes a mesh surface using an implied surface from a boundary spline curve and mesh generated using DiscreteGraphics, I need to identify the Vertices and Lines around the edges ...

asked by mh2000 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=57215 7 votes

answered by Tim Laska https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=61809 8 votes

How can I extract the edge points from an image?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233092

I want to extract the edge points from a text image and use ListPlot[points] to visualize those points:

I tried to used ...

asked by vito https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=30288 7 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 9 votes

How to speed up integers finding function?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=232960

Playing with integers I looked for a way of finding, let’s say, \(4\)-digits positive integers such that \(a,b,a+b\) had the same digits, like \[1089 + 8019 = 9108\] I am a newbie and I used this function

asked by Raffaele https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=49764 7 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 12 votes

2.9.2 Greatest hits from previous weeks

Where can I find examples of good Mathematica programming practice?
Plotting a Phase Portrait
How can I save both the plot and the legend together?
Find eigen energies of time-independent Schrödinger equation
xkcd-style Plots
How to create a new "person curve"?
How to plot an ellipse?

Where can I find examples of good Mathematica programming practice?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=18

I consider myself a pretty good Mathematica programmer, but I’m always looking out for ways to either improve my way of doing things in Mathematica, or to see if there’s something nifty that I haven’t ...

asked by J. M.’s discontentment https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=50 553 votes

answered by faysou https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=66 486 votes

Plotting a Phase Portrait

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=14160

I’m trying to plot a phase portrait for the differential equation \[x'' - (1 - x^2) x' + x = 0.5 \cos (1.1 t)\,.\] The primes are derivatives with respect to \(t\). I’ve reduced this second order ODE to ...

asked by covertbob https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4528 38 votes

answered by David Slater https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1746 33 votes

How can I save both the plot and the legend together?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=35653

In this example, how can I put the legend inside the graph? Currently, when I save the graph, only the graph is saved, not the legend.

asked by Mika Ike https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6543 42 votes

answered by C. E. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=731 38 votes

Find eigen energies of time-independent Schrödinger equation

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=32293

I’m trying to get the eigenvalues of a one dimensional time-independent Schrödinger equation,

\(-\frac {h^2}{2m_0}\frac {d^2\psi }{dx^2}+U(x)~\psi =Ei~\psi \)

where U(x) is some potential and Ei is the ...

asked by xslittlegrass https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=1364 48 votes

answered by Jens https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=245 46 votes

xkcd-style Plots

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=11350

I received an email to which I wanted to respond with a xkcd-style graph, but I couldn’t manage it. Everything I drew looked perfect, and I don’t have enough command over ...

asked by Amatya https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2039 616 votes

answered by Simon Woods https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=862 474 votes

How to create a new "person curve"?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=17704

Wolfram|Alpha has a whole collection of parametric curves that create images of famous people. To see them, enter WolframAlpha["person curve"] into a Mathematica ...

asked by Simon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=34 83 votes

answered by Vitaliy Kaurov https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=13 45 votes

How to plot an ellipse?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=20100

I’m new to Mathematica, and I’m finding it difficult to plot an ellipse. I tried using

Plot[(x/5)^2 + (y/3)^2 == 1, {x, -5, 5}, {y, -3, 3}]

but I’m getting ...

asked by Sriram https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6075 17 votes

answered by Jens https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=245 29 votes

2.9.3 Can you answer these questions?

Equation of Motion: Perturb Scalar Field and flat FLRW Metric (xAct)
Is there any way to change the box-formatting behavior thoroughly?
How to get colors at points in Graphics3D?

Equation of Motion: Perturb Scalar Field and flat FLRW Metric (xAct)

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233105

Is there a way to get the equations of motion (eom) of a scalar field from a Lagrangian in a perturbed FLRW metric? I want to perturb the field as well as the metric to 1st order. What I did so far:

asked by kalle https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=68748 1 vote

Is there any way to change the box-formatting behavior thoroughly?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233100

Background The box-formmating behavior is affected by the downvalues of the symbol MakeBoxes. But the formatting behavior is not exactly ...

asked by asd1dsa https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72876 2 votes

How to get colors at points in Graphics3D?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=233287

To get the color at a 2D point in Graphics you can Rasterize it and look up the pixel value, but not for ...

asked by M.R. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=403 2 votes