3.1.1 Top new questions this week

3.1.1.1 Eigenvalues broken in 11.2?

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165354

Bug introduced in 11.1.0

The code

M = Flatten[Table[Flatten[Transpose[{{1, a, a, -1}[[i]] 
            UnitVector[4, i]}].{{1, a, a, -1}[[j]] 
            UnitVector[4, j]}],   {i, 1, 4}, {j, 1,  ...
 

asked by Matthias 19 votes

answered by Szabolcs 17 votes

3.1.1.2 mplementing a chat system in Mathematica

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165667

My friends and I don’t want to use Slack or Gitter, but instead a pure-Mathematica chat system.

Now that the ChannelFramework exists, how could we do this?

asked by b3m2a1 17 votes

answered by b3m2a1 19 votes

3.1.1.3 What to expect from Interpreter["Expression"]?

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165685

Sometimes it works ok

Interpreter["Expression"]["1"] 
 
  1
 

sometimes not:

Interpreter["Expression"]["Graphics[{}]"]
 

Why doesn’t it work for the second case? What is the rule of thumb here?

asked by Kuba 14 votes

answered by Michael E2 12 votes

3.1.1.4 How to compute intersections of circles on a lattice?

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165462

Take a set of points in the plane and draw a circle of a given radius at each point. The resulting pattern of circles may look something like this:

Graphics[Circle[#, 9/10] & /@ Tuples[Range[7],  ...
 

asked by Ben 12 votes

answered by kglr 12 votes

3.1.1.5 RandomChoice output isn’t packed

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165440

Why isn’t the output of RandomChoice a packed array? For instance:

RandomChoice[{.5, .2, .3} -> {1, 2, 3}, 10] 
Developer`PackedArrayQ @ % 
 
  {1, 2, 3, 1, 3, 1, 1, 2, 3, 3} 
 
  False
 

asked by Carl Woll 12 votes answered by Carl Woll 13 votes

3.1.1.6 Piecewise-constant function with infinitely many pieces

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165673

How can I define the following function in Mathematica:

\[f(x)=\begin {cases} x-n,&\mbox {when $2n\le x\le 2n+1$,}\\n+1,&\mbox {when $2n+1\le x\le 2n+2$,}\end {cases}\]

where \(n\) takes all

asked by Erel Segal-Halevi 9 votes

answered by b3m2a1 11 votes

3.1.1.7 Get title of a webpage only?

https://mathematica.stackexchange.com/landing/r/newsletter?cta=question&id=165557

Is it possible to use Mathematica to obtain just the title of a webpage? (I mean the small amount of text that appears in the webpage tab at the top of a browser.)

Every standard HTML page must have ...

asked by Kagaratsch 9 votes

answered by eyorble 11 votes