8.2.3 Can you answer these questions?

8.2.3.1 Sum of list elements in a range

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=262276

I have a list, for example: 
 data = {1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20}; 
 
and I wanted to sum every element in range of five, i. e 
ranges 
... 
[list-manipulation] [summation]
 

asked by Pawe Chmolewski https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=69008 1 vote

8.2.3.2 Is it possible to add "Synonyms and Antonyms" to the rightclick menu like office word and do the replacement in place?

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=262401

When we write some note or comments in the notebook, Mathematica provides an spell check and we can select the right word to make it right. Mathematica 12.0 also provides a function to find the ... 
[replacement] [notebooks]
 

asked by hlren https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=54486 1 vote

8.2.3.3 Unable to implement boundary conditions for a spherical wave equation coupled to a Laplace equation

https://mathematica.stackexchange.com/landing/r/digest?cta=question&id=262261

I am having trouble setting up in Mathematica v 12.1 the following 
system of coupled pdes on $r\in[0,10]$ 
$$ \left(\partial_t^2 - \frac{1}{r^2}\partial_r r^2 \partial_r \right) \theta(t,r) = -(1+2\Phi(... 
[differential-equations] [boundary-conditions]
 

asked by Rudyard https://mathematica.stackexchange.com/landing/r/digest?cta=user&id=58654 1 vote