Using a vector as column-indices into rows of a matrix, in Octave

You need to create linear indices for that. Following your example:

octave-3.8.2> a = [1  2  3
                   4  5  6
                   7  8  9];
octave-3.8.2> b = [1 3 1];
octave-3.8.2> ind = sub2ind (size (a), 1:rows (a), b);
octave-3.8.2> c = a(ind)
c =

   1   6   7

As per my understanding, the way to go about creating a logical matrix is below:

>A = eye(3,3)

>B = [1;3;1]

>A(B,:) =
>
>[ 1   0   0;
>  0   0   1;  
>  1   0   0; ]