2.23 Thursday, June 25, 2020

2.23.1 Top new questions this week
2.23.2 Greatest hits from previous weeks
2.23.3 Can you answer these questions?

2.23.1 Top new questions this week

Version 12.1.1 unable to type ">"
Is there any better way to create a, a, a, b, b, b, b, b, c, c from a, 3, b, 5, c, 2?
Selecting lists where all are prime
Inverting replace direction
Calculate Radius of Curvature
Legendre expansion of the Dirac delta function
Which methods are available for NDEigensystem?

Version 12.1.1 unable to type ">"

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224461

Bug introduced in 12.1.1

Since I upgraded to version 12.1.1 I am unable to use > (Shift+.). When I type Shift+. the cell that I am typing in converts to Python. What am I doing wrong?

Steps to ...

asked by wdacda https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=27856 15 votes

answered by Mr.Wizard https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=121 10 votes

Is there any better way to create a, a, a, b, b, b, b, b, c, c from a, 3, b, 5, c, 2?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224581

My attempt:

data = {{a, 3}, {b, 5}, {c, 2}}; 
 
output = Table[#[[1]], #[[2]]] & /@ data // Flatten 
 
{a, a, a, b, b, b, b, b, c, c}

asked by Too Fat Man No Neck https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=42141 11 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 18 votes

Selecting lists where all are prime

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224500

Given

    t={{7, 13, 19}, {13, 25, 37}, {19, 37, 55}, {25, 49, 73}, {31, 61, 91}, {37, 73, 109}} 
 
I want to select those lists where all three numbers are primes, so I should get 
{{7, 13, 19}, {37,  ...

asked by user57467 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=57467 9 votes

answered by Pillsy https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=531 12 votes

Inverting replace direction

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224314

I just have a simple problem. I have a list such that,

rep = { a1 -> b1, a2 -> b2, a3 -> b3}; 
 
I want to invert replace direction such that, 
{ b1 -> a1, b2 -> a2, b3 -> a3}

asked by Saesun Kim https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=29998 8 votes

answered by PaulCommentary https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=54458 8 votes

Calculate Radius of Curvature

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224269

I have a list of coordinates that make a near-parabolic graph, which I managed to fit and calculate the curvature. However, the curvature only outputs a equation. Is there any way to calculate the ...

asked by Char https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=66040 8 votes

answered by yarchik https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9469 11 votes

Legendre expansion of the Dirac delta function

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224276

There is a known expansion for the Dirac delta function in the interval \( (-1, 1) \) in terms of the Legendre polynomials as

$$\delta(x) = \sum_{k = 0}^{\infty} (-1)^k \frac{(4k + 1) (2k)!}{2^{2k + 1}

asked by Novice https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72595 7 votes

answered by yarchik https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9469 11 votes

Which methods are available for NDEigensystem?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224511

I am trying to find out what methods/options are available for NDEigensystem and descriptions of their use. Perusing the help, online Q&As, Mathematica’s in-line autofill, etc., I’ve found a few, ...

asked by Eli Lansey https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9 6 votes

answered by user21 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=18437 5 votes

2.23.2 Greatest hits from previous weeks

How can I save both the plot and the legend together?
Formatting legend text font
QR Code in shopping cart handle
Solving \(L=\frac {3}{2} \sqrt {4 \pi ^2 A^2+W^2}-\frac {\sqrt {5 W \sqrt {4 \pi ^2 A^2+W^2}+6 \pi ^2 A^2+3 W^2}}{\sqrt {2}}+\frac {3 W}{2}\) for \(W\)
1 Plot, 2 Scale/Axis
What are the most common pitfalls awaiting new users?
How to express trigonometric equation in terms of of given trigonometric function?

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.

Expr1 = -2 p + 1 
Expr2 = 2 p - 1 
Expr3 = p - 1/2 
Plot[{Expr1,  ...

asked by Mika Ike https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=6543 41 votes

answered by C. E. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=731 35 votes

Formatting legend text font

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=3433

I am using this code to plot a graph, and I am trying to make the font of the legend bigger.

<<PlotLegends` 
ListLogLogPlot[{Sort[moby]}, PlotRange -> Full, Joined -> True,

asked by Julia https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=525 20 votes

answered by kglr https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=125 25 votes

QR Code in shopping cart handle

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=26268

This week, the market people from my work wanted to put QR codes in shopping cart handles, but when they tested it, the QR code did not work. I noted that the cylindrical curvature (even small) ...

asked by Murta https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=2266 194 votes

answered by halirutan https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=187 190 votes

Solving \(L=\frac {3}{2} \sqrt {4 \pi ^2 A^2+W^2}-\frac {\sqrt {5 W \sqrt {4 \pi ^2 A^2+W^2}+6 \pi ^2 A^2+3 W^2}}{\sqrt {2}}+\frac {3 W}{2}\) for \(W\)

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=57763

When I solve the aforementioned equation for \(W\) or \(A\) on Mathematica I get a long and ugly equation in return, namely one of the solutions for \(W\) is: (attempt to read at your own health)

asked by J.D’Almbert https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=19257 8 votes

answered by Alexei Boulbitch https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=788 14 votes

1 Plot, 2 Scale/Axis

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=627

I would like to plot those two datasets on top of each other. But they have very different range on the \(y\) axis. How can I have two different axis?

I found the following on the help menu but quite ...

asked by 500 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=172 145 votes

answered by ArgentoSapiens https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=92 149 votes

What are the most common pitfalls awaiting new users?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=18393

As you may already know, Mathematica is a wonderful piece of software. However, it has a few characteristics that tend to confuse new (and sometimes not-so-new) users. That can be clearly seen from ...

asked by Dr. belisarius https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=193 462 votes

answered by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 279 votes

How to express trigonometric equation in terms of of given trigonometric function?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=434

How can I express a trigonometric equation / identity in terms of a given trigonometric function?

using following trigonometric identities

Sin[x]^2+Cos[x]^2==1 
Sin[x]/Cos[x]==Tan[x]

asked by Prashant Bhate https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=99 30 votes

answered by Simon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=34 37 votes

2.23.3 Can you answer these questions?

Using RegionPlot with NDSolve
Implementing binomial expansion of (non-commuting) matrices in Mathematica
Acquiring images from Zwo ASI camera in Mathematica Home Edition v 11.2.0.0

Using RegionPlot with NDSolve

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224477

So I have a DE which has no analytical solution and thus solved using NDSolve, involving some parameters like this:

solution=NDSolve[{b/z[t]^4+a z'[t]+z''[t]==0,z[0]==3,z'[0]==3},z,{t,0,5}]

I was ...

asked by t-smart https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=53560 1 vote

Implementing binomial expansion of (non-commuting) matrices in Mathematica

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224402

Given two matrices \(A\) and \(B\), their Binomial expansion is, in general, given by (see this page) \((A+B)^n = \sum \limits _{k=0, k=n[2]}^n \Bigg ( \sum \limits _{r=0}^k \binom {k}{r} A^r B^{k-r} \Bigg )\) ...

asked by Rob https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=66809 1 vote

answered by flinty https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=72682 0 votes

Acquiring images from Zwo ASI camera in Mathematica Home Edition v 11.2.0.0

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=224258

I plan to use a ZWO ASI planetary camera (USB connection) for astronomical photography and would like to control the image acquisition using Mathematica. The issue is that although I have installed ...

asked by Dave Baker https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=73406 1 vote