More on subscripting
The colon operator can be used to access arbitrary slices of an array.
a(2:3, 1:2) % rows 2-3, cols 1-2
a(1:2, 4) % rows 1-2, col 4
a(1:2, :) % rows 1-2, all cols
It can also be used to change the shape of an array by deleting rows, columns, or sub-matrices of a matrix.
a(1:2, :) = [] % removes rows 1-2