Problem in using loops - how to have index inside a loop

Hi all,

"a" contains index, Vb contains values

for example,

inputs: vref= 20 a=[2 4 6 9] Vb=[ 8 9 1 7 5 3 6 55 8 7]

output: (9 plus with 1 gives 16) sum_Bank1 = 16

What I want to do:

If sum_Bank1 is greater than vref, i want the system to divide Bank1 into half again, and check if sum_Bank3 is still greater than vref, if it is, Bank3 is divided by half again, this process is repeated for many times until certain condition.

My question is, how can I write it in a loop instead of repeat the same codes many times?

function [sum_Bank1] = division(a, vref)
dimen = size (a); 
    ncol = dimen (2); % ncol=4
    Bank1= a(:, 1:ncol/2); % Bank1 = [2 4]
    Bank2= a(:, ((ncol/2) + 1):ncol); % Bank2 = [6 9]
    sum_Bank1=sum(Vb(Bank1)); % sum_Bank1 = 16
    sum_Bank2=sum(Vb(Bank2)); % sum_Bank1 = 11
    if sum_Bank1 > vref
        Bank3= Bank1(:,1:ncol/2);
        Bank4= Bank1(:, ((ncol/2) + 1):ncol);
    if sum_Bank3 > vref
        Bank5= Bank3(:,1:ncol/2);
        Bank6= Bank3(:, ((ncol/2) + 1):ncol);
      if sum_Bank5 > vref
        Bank7= Bank5(:,1:ncol/2);
        Bank8= Bank5(:, ((ncol/2) + 1):ncol);