8.6.3 Can you answer these questions?

8.6.3.1 Threshold on triangular SparseArray

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=263605

I am confused by the behavior of  Threshold  on sparse  UpperTringularize  (and  LowerTringularize ... 
[linear-algebra] [sparse-arrays]
 

asked by Markus Roellig https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=135 Score of 2

8.6.3.2 How to fix Mathematica crashing in the following case?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=263478

I have a problem with Mathematica when trying to glue two tables together. 
The tables have the form 
... 
[table] [code-review] [crash] [broken-code]
 

asked by John Taylor https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=41058 Score of 1

8.6.3.3 Two Coupled First Order Differential Equations

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=263465

I'm trying to solve the following differential equations. The 4 boundary conditions imposed are based on physical grounds required for regularity at the origin. It is known that these equations do not ... 
[plotting] [differential-equations] [boundary-conditions]
 

asked by Impala https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=85033 Score of 1