For background, we start with an overview of the matrix command:

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Result

matrix { a # b ## c # d }

Rows are separated by two #'s and entries within each row are separated by one #.

The first problem people have with matrices is that brackets do not “scale" with the matrix:

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Result

( matrix { a # b ## c # d } )

()

OOoMath provides “scalable" brackets. That is, the brackets grow in size to match the size of their contents. Use the commands left( and right) to make scalable brackets.