Help with vectorization of my code

Hello all. I have a code like below

   cd = [21543;21544;21545;21546;21547;21548;21549];
   for i=1:7
     K(2*cd(i)-1,2*cd(i)-1)= K(2*cd(i)-1,2*cd(i)-1) + St(1,1,i);
     K(2*cd(i)-1,2*cd(i))= K(2*cd(i)-1,2*cd(i)) + St(1,2,i);
   end

K is a sparse matrix of size [44044 x 44044] and 'St' is a 3D array. I've tried to vectorize this code with no success. Could anyone please help?

Thanks.

[Geoff Hayes]

Saipraneeth - you should avoid naming variables after built-in MATLAB functions (i.e. http://www.mathworks.com/help/matlab/ref/cd.html).

Also, please clarify what the problem is with the above code. Does it take a while to execute?

[Saipraneeth]

Thanks for the reply. I named it 'cd' just for writing it here, it's different in my actual code.

Actually, the problem is this code is inside another loop with around 20 iterations. The 'cd' vector changes in every iteration and becomes big like (9000 x 1), which is the maximum size 'i' will take. So, it does take a while and I am trying to reduce it. Is there any way to vectorize it?

[Walter Roberson]

... do not allow it to grow in size. Assign it the maximum size before the loop. It will speed up your code a lot.