2.1.2 Greatest hits from previous weeks

Greatest hits from previous weeks:

2.1.2.1 Matrix in Latex

http://tex.stackexchange.com/questions/204621/matrix-in-latex

I am new to Latex, and I have been trying to get the matrix of following form 
[x11 x12 x13 . . . . x1n 
x21 x22 x23 . . . . x2n 
. 
. 
. 
. 
xd1 xd2 xd3 . . . . xdn] 
...
 

- asked by Lakshmi Narayanan (16 votes), answered by skpblack (35 votes)

2.1.2.2 Commenting out large sections

http://tex.stackexchange.com/questions/17816/commenting-out-large-sections

So to "comment out" a line, I need to insert a % at the beginning of the line (so that line will not be compiled). 
Is there way to comment out a large section without having to manually putting a %  ...
 

- asked by user5419 (144 votes), answered by Martin Scharrer (118 votes)