Question

Suppose I have:

>> X = magic(5)
X =

   17   24    1    8   15
   23    5    7   14   16
    4    6   13   20   22
   10   12   19   21    3
   11   18   25    2    9

How do I get i’th element from the second column?

I already figured that indices in (some?) collections in Octave are one-based, but I’m not sure if that holds for matrices, too.

Answer 1

See the index expressions section of the manual. To get the i’th element from second column:

X(i,2)      # element 'i' from column 2
X(1:end,2)  # the whole 2nd column
X(:,2)      # same thing but shorter
x(:, [2 3]) # whole 2nd and 3rd column

Note that Octave is a language where array elements are in column-major order.