manipultion of matrix element

hi! i have as an example this matrix (my matrix is big):

 %
A=[a1 a2 a3 a4 a5 a6 a7; b1 b2 b3 b4 b5 b6 b7; c1 c2 c3 c4 c5 c6 c7]
how could i build 
f=[a1 a3 a5 a7;b1 b3 b5 b7;c1 c3 c5 c7] ?

thank you

Answer 1

[Matt J]

f=A(:,1:2:end);