MATLAB: How to extract column in particular interval from original matrix and to form new matrix

Question

i have matrix of size 50*1000. i want to extract the column in the interval of 3.(1,4,7,10 etc..). when i used for loop, it overriding column every iteration. but i need to store column extracted in each iteration to stored in new matrix. could you please point out where done mistake in below coding? thanks in advance

L3 is matrix size of 50*1000

[r1,c1]=size(L3)

for i1=1:3:c1

   L4=L3(:,i1);
   end

L4 is new matrix

Answer 1

L4 = L3(:,1:3:end);