To plot a matrix, use the following syntax:
matrix( siseX, sizeY, element_11, element_12, .... )
This draws a matrix of dimensions sizeX and sizeY. The quantity of elements should be, obviously, sizeX multiplied by sizeY.
Elements of the matrix are expressions of any complexity.
Example of a 2x3 tall matrix:
matrix( 2, 3, 1, 2, 3, 4, 5, 6 )
Note that matrix plots a matrix NOT enclosed in brackets. If you want it enclosed in brackets, please use brackets outside it:
( matrix( 2, 2, 1, 2, 3, 4 ) )