How to add or multiply two different size of array using the loop iteration process?

How to add or multiply two different size of array using the loop iteration process? suppose ,an array

a=[1 2 3 4 5 6 7 8 9 ]
b=[1 2 3 ]

and i want increase the size of the 'b' array using. for loop. as like the value of 'b' after using for loop is

= [1 2 3 1 2 3 1 2 3]

Then, we will add or multiply this array.That will very much appreciating if anyone can give a matlab code for this problem....

Answer 1

[Andrei Bobrov]

bnew = repmat(b,1,numel(a)/numel(b))

[Saiem Solimullah]

this is working but how can i do this process by using for loop??

[Andrei Bobrov]

na = numel(a);
nb = numel(b);
bnew = a;
for ii = 1:na/nb
    bnew(nb*(ii-1)+1 : nb*ii) = b;
end

[Saiem Solimullah]

this code will not work due to its diffrent length of b

Answer 2

[Jos (10584)]

    a = [1 2 3 4 5 6 7 8 9 ]
    b = [1 2 3 4] % Generic case: numel(a) is not a multiple of numel(b)

    nb = numel(b) ;
    for ka=1:numel(a)
       kb = rem(ka-1,nb)+1 ;
       c(ka) = a(ka) * b(kb) ;
    end

But this can be vectorised, to make it more efficient:

kb = rem(0:numel(a)-1,nb)+1 
c = a .* b(kb)