Need clarity of this command

I am having these commands

a = [697 770 852 941]; 
b = [1209 1336 1477];  

%them later in code
f  = [];   
for c=1:4,
    for r=1:3,
        f = [ f [a(c);b(r)] ]; % WHAT IS function of this command
    end
end

Plz explain this command

f = [ f [a(c);b(r)] ];

and what does this do

 f  = [];  %does it make empty matrix

Answer 1

[Fangjun Jiang]

You are right.

f=[]; % make f an empty matrix

a=1;b=2;
f=[a;b] % doing vertical concatenation
f=[a b] % doing horizontal concatenation

doing f=[f [a(c);b(r)] ] in a loop is expanding f. It's not a good programming technique though.

Answer 2

[moonman]

So kindly tell me the good way to do this as i am also confused abt this statement of book

f = [ f [a(c);b(r)] ]; why f is written in the bracket

[Fangjun Jiang]

Start f as [], just run the following one at a time to test it out.

f=[f [1;2]]

f=[f [3;4]]

f=[f [400;500]]