A = rand(900,15);
first_col = A(3:end,1);
portion = A(33:58,1);
always remember that when you are indexing inside a matrix, the first argument refers to the rows while the second argument refers to columns. inside these arguments you can pass vectors that contain the keys for rows and columns elements you are interested in (like the number and letter of a labeled seat in a Cinema).
so in this excercize, you want the first column, so the second argument will be always a vector containing only the lement "1", while for the rows you build:
- a vector [3 4 5 6 ... end] to take the last n_rows - 2 elements
- a vector [33 34 35 ... 58] to take the portion of interest.