12.13.1 Top new questions this week

12.13.1.1 Plotting a function with constraint
12.13.1.2 Fast/Easy way to decompose a block matrix?
12.13.1.3 How to obtain this asymptotic of the sum of the series?
12.13.1.4 Why is `CoefficientRules` significantly slower than `CoefficientList`, and how to efficiently get sparse rules for multivariate polynomials?
12.13.1.5 Why don't these rules work?
12.13.1.6 How to compute the semidirect product of groups, for example Z_5 and Z_2, using Mathematica?
12.13.1.1 Plotting a function with constraint

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319164

I have a matrix 
 M = {{-num11/(2*den), num12/den}, {num12/den, num22/(2*den)}}; 
 
with 
... 
[equation-solving] [symbolic] [constraint] [findinstance]
 
asked by Rob https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=66809 Score of 6
12.13.1.2 Fast/Easy way to decompose a block matrix?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319155

I am solving a system of nonlinear PDE (1 time, 1 space). I spatially discretize them into vectors n+2 long (the extra 2 being the boundary points). This often leaves me with 2n x 2n Jacobian to ... 
[matrix] [linear-algebra] [nonlinear]
 
asked by DGC https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=111367 Score of 6
answered by Michael E2 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=4999 Score of 10
12.13.1.3 How to obtain this asymptotic of the sum of the series?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319159

The results of the commands in 14.3 on Windows 
 AsymptoticSum[(-1)^(k - 1)/k, {k, 1, n}, {n, Infinity, 1}] 
 
 
... 
[calculus-and-analysis]
 
asked by user64494 https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=7152 Score of 5
answered by Mariusz Iwaniuk https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=26828 Score of 7
12.13.1.4 Why is `CoefficientRules` significantly slower than `CoefficientList`, and how to efficiently get sparse rules for multivariate polynomials?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319163

I have noticed a significant performance gap between  CoefficientList  and  CoefficientRules . While ... 
[performance-tuning] [polynomials] [sparse-arrays] [internals]
 
asked by lapcal https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=85338 Score of 4
12.13.1.5 Why don't these rules work?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319167

I have written the following code that should help me to rewrite a complicated expression in terms of Lorentz invariants that I have called $I_4,I_8$ and so on. 
... 
[replacement] [tensors] [rule] [xact]
 
asked by Filippo https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=116563 Score of 3
answered by mikado https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=36788 Score of 2
12.13.1.6 How to compute the semidirect product of groups, for example Z_5 and Z_2, using Mathematica?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=319151

I need a way to automate calculation of the semidirect product of $Z_p$ and $Z_n$ where $n$ divides $p-1$ and $p$ is prime, with Mathematica in terms of Mathematica's default permutations notation. A ... 
[linear-algebra] [group-theory]
                                                                                  

                                                                                  
 
asked by Phillip Dukes https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=94691 Score of 2
answered by A. Kato https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=62063 Score of 8