[Tex/LaTex] How to add tabular lines, matrix lines to arrays in LyX

Question

The buttons such as Set all lines, Set right line, Set left line and Set bottom line are not activated with arrays as the example on the left while they are activated on the example on the right with tabular environment.

My goal is to learn to create upper triangularizations like on the right below. For that one needs to turn the array into tabular environment somehow or find a way to get the line options in matrices/arrays/tabulars activated.

How can I add the tabular lines or matrix lines in LyX?

Answer 1

1. Method: Add modifications directly to the option Horizontal: like in tabular environment in LaTeX.

2. Method: Click the right mouse button and choose one of the Add line options.

for example Add Line Above and ^M W A, ^M W Z in the dropdown.

3. Method: use the panel pictures a bit like in Word (feature that works every-now-and-then, perhaps a bug in LyX 2.1.4?)