Creating a Macro for an n-by-m Matrix in LyX

Question

Specifically, I'd like to create a matrix such as

$\left[\begin{array}{cc|c}
a_{1} & a_{2} & a_{3}\\
b_{1} & b_{2} & b_{3}\\
c_{1} & c_{2} & c_{3}
\end{array}\right]$

But in an arbitrary fashion in LyX. I'd like to do this in a way the utilizes the fact that LyX displays the 'boxes' where one can put in numbers, as opposed to typing it in beforehand. Although, I'd be fine in doing it without that feature. So far, I've only been able to create a very basic macro in my own .sty file defining a 2x2 matrix but I cannot get LyX to display the 'boxes' and can only get the macro to work if I add in curly braces and put in the numbers myself.

I should add that I'm decent at LyX and TeX, but no expert by any stretch of the imagination. My use is restricted to its capabilities as a note taking device, as my handwriting has always been illegible. However, I can follow some of the technical jargon, so don't be too afraid to throw something at little specific at me!

Thanks in advance!

Answer 1

To explain it more detailled as in @Andrew's comment (there a some curly braces missing at the end).

I will explain it in two ways: the LyX and the LaTeX coding way.

LyX macro input

Insert a new blank macro by clicking on menu "View > Math > Macro". A macro field with prefilled macro name "\newmacroname" is inserted:

Change "\newmacroname" to the name you like, here e.g. "\MyMat". Then place the cursor in the blue field on the right, labelled "LyX". Put in the math stuff you want. Insert placeholders (1st: \#1, 2nd: \#2, ...) for each parameter on the place where you want them. For your example it would like that*:

And that's it. You can use the macro right away in math mode. Just type \MyMat. Now if you type in the first placeholder, every other place with the same placeholder is automatically also filled.

• There seems to be a bug with inserting the vertical line in the matrix, so you must use decoration type "None" and horizontal alignment "cc|c".

LaTeX newcommand input

Copy the this code as text in LyX:

\newcommand{\MyMat}[3]{
        \left[
                \begin{array}{cc|c} 
                    #1_1 & #1_2 & #1_3\\ 
                    #2_1 & #2_2 & #2_3\\
                    #3_1 & #3_2 & #3_3 
                \end{array}
        \right]
}

Highlight it and turn it to math mode (Ctrl + M). Then you can use it right away as a macro in math mode (like above). Or write in text mode \MyMat{a}{b}{c} and convert it also in math mode, then it will be already filled. That's pure LaTeX (-;