GNU Octave

Time for action – manipulating arrays

1. To delete the second column in A, we use:

   octave:14> A(:,2) = []
   
   A =
     1   3
     1   3
   

2. We can extend an existing array, for example:

   octave:15 > b = [b 4 5]
   
   b =
     1 2 3 4 5
   

3. Finally, try the following commands:

   octave:16> d = [2 4 6 8 10 12 14 16 18 20]
   
   d =
     2    4    6    8    10    12    14    16    18    20
   
   octave:17> d(1:2:9)
   
   ans =
     2    6    10   14    18
   
   octave:18>  d(3:3:12) = -1
   
   d =
     2    4    -1    8    10    -1    14    16    -1    20    0    -1
   

What just happened?

In Command 14, Octave interprets [] as an empty column vector and column 2 in A is then deleted in the command. Instead of deleting a column, we could have deleted a row, for example as an empty column vector and column 2 in A is then deleted in the command.

octave:14> A(2,:)=[]

On the right-hand side of the equal ...