5.4.1 Top new questions this week

5.4.1.1 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,  ... 
[bugs] [eigenvalues]
 

asked by Matthias https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=55121 19 votes

answered by Szabolcs https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=12 17 votes

5.4.1.2 Implementing 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? 
 
[object-oriented] [channel-framework]
 

asked by b3m2a1 https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=38205 17 votes

answered by b3m2a1 https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=38205 19 votes

5.4.1.3 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? 
 
[functions] [documentation] [free-form-input] [interpreter]
 

asked by Kuba https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=5478 14 votes

answered by Michael E2 https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=4999 12 votes

5.4.1.4 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],  ... 
[regions] [intersection]
 

asked by Ben https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=16130 12 votes

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

5.4.1.5 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 
 
 
[packed-arrays]
 

asked by Carl Woll https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=45431 12 votes

answered by Carl Woll https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=45431 13 votes

5.4.1.6 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  ... 
[piecewise]
 

asked by Erel Segal-Halevi https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=49101 9 votes

answered by b3m2a1 https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=38205 11 votes

5.4.1.7 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  ... 
[web-access] [url]
 

asked by Kagaratsch https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=5517 9 votes

answered by eyorble https://mathematica.stackexchange.com/landing/r/newsletter?cta=user&id=52935 11 votes