To remove every other column, set it to empty. You can do "every other" generally using A:2:B where A is the first value and B is the last value, and you can stick this in as an index.
a=reshape(1:25,5,5)
a1=a;
a1(1:2:end,:)=[] % remove every other row
a2=a;
a2(2:2:end,:)=[] % remove every other row starting at the second row
a3=a;
a3(:,1:2:end)=[] % remove every other column
a4=a;
a4(:,1:2:end)=0 % set every other row/column to 0
% If you really feel like you have to do both at once, you can. But it
% would be much easier to just do rows and columns sequentially.
a5=a;
[r,c]=meshgrid(1:size(a5,1),1:size(a5,2));
ind=sub2ind(size(a5),r(mod(r,2)==0 | mod(c,2)==0),c(mod(r,2)==0 | mod(c,2)==0));
a5(ind)=0
