MATLAB 2

A=[1,2,3;4,5,6;7,8,9];B=zeros(3,2); C=zeros(1,5); D=[A,B;C];D
D =
     1     2     3     0     0
     4     5     6     0     0
     7     8     9     0     0
     0     0     0     0     0

E=[1,2,4,8,16];F=diag(E)
F =
     1     0     0     0     0
     0     2     0     0     0
     0     0     4     0     0
     0     0     0     8     0
     0     0     0     0    16

G=F(:,3)
G =
     0
     0
     4
     0
     0