11.24.1 Top new questions this week

11.24.1.1 How do I display any given expression in postfix notation rather than the standard notation?
11.24.1.2 How to swap two columns in a specific row of a matrix?
11.24.1.3 Why `MatchQ[ 3 + x, _ + _ ]` return `False`?
11.24.1.4 Generating Poincaré sections
11.24.1.5 Combining exterior derivatives with endomorphisms
11.24.1.6 Prepending line number when outputting
11.24.1.7 What is the root cause for "PacletToolsGeneral::error: "PacletInfo.m" is not a properly formatted PacletInfo.wl or PacletInfo.m file." in PacletBuild
11.24.1.1 How do I display any given expression in postfix notation rather than the standard notation?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314417

My example is 
 f[f[f[startValue, 1], 2], 3] 
 
which I would like to display as 
 f[startValue, 1] // f[#, 2]& // f[#, 3]& 
 
... 
[core-language] [notation]
 
asked by PaulCommentary https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=54458 Score of 9
answered by E. Chan-López https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=53427 Score of 8
11.24.1.2 How to swap two columns in a specific row of a matrix?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314399

What I've tried is the following: 
... 
[list-manipulation] [functions]
 
asked by Phillip Dukes https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=94691 Score of 6
answered by Nasser https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=70 Score of 6
11.24.1.3 Why `MatchQ[ 3 + x, _ + _ ]` return `False`?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314446

Consider 
 MatchQ[ 3 + x, _ + _ ] 
 
It returns  False . Why? 
After some research, I concluded that it's due to the ... 
[pattern-matching]
 
asked by lezambranof https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=82626 Score of 4
answered by Greg Hurst https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4346 Score of 11
11.24.1.4 Generating Poincaré sections

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314415

I would like to reproduce the Poincaré sections presented in this and this papers, which look like 
 
The figures are for energy values of E=0.2 (a) and E=0.25 (b) in the Hamiltonian, which reads 
$$H=\... 
[differential-equations] [equation-solving] [calculus-and-analysis] [numerical-integration]
 
asked by Shasa https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=58680 Score of 4
answered by Alex Trounev https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=58388 Score of 2
11.24.1.5 Combining exterior derivatives with endomorphisms

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314424

(I am a Mathematica novice, please be gentle) I am trying to perform an explicit but lengthy tensor computation and from what I can tell the xterior.m package has much of the functionality I need but ... 
[tensors]
 
asked by Thisquestionisreallyhard https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=111214 Score of 3
11.24.1.6 Prepending line number when outputting

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314418

My goal is to input multiple lines in the same cell and prepend line numbers when outputting. I've tried within my knowledge, but as you can see,  Row[]  and ... 
[formatting] [cells]
 
asked by Soon https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=78050 Score of 3
answered by Nasser https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=70 Score of 7
11.24.1.7 What is the root cause for "PacletToolsGeneral::error: "PacletInfo.m" is not a properly formatted PacletInfo.wl or PacletInfo.m file." in PacletBuild

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=314397

Here is my PacletInfo.m: 
... 
[packages]
 
asked by Satrajit Roy https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=80872 Score of 3
answered by Jason B. https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=9490 Score of 4