Here is an example of how to create a matrix with Collabora Office Math. If you want to use the example in your own formula, you can copy it to the Commands window using the clipboard.
font sans bold size *2 A =left[matrix{A_11#A_12#dotsaxis#A_{1n}##A_21#{} #{}#A_{2n}##dotsvert#{}#{}#dotsvert##A_{n1}#A_{n2}#dotsaxis#A_nn}right]
