MATLAB: Question about vectorization using indexes

MATLABvectorization

Hello, I am trying to do the following operations in matlab but I have a problem with how to properly write my code using vectorization. This is just an example, m, n and the values of the vectors and matrices are just to illustrate my problem. In reality m and n can go up to 1000. 
n=5; m=8;
a=4*ones(m,1); a(2)=2;a(n)=3;
b=2*ones(n,2);b(1,1)=5;b(3,1)=1;
ind=3*ones(n,2); 
ind(1,2)=0;ind(3,2)=0; b(1,2)=0;b(3,2)=0;
non=zeros(1,n);c=zeros(1,n);
for i=1:n
    non(i)=nnz(ind(i,:));
    c(i)=prod(a(ind(i,1:non(i)))'.^b(i,1:non(i)),2);
end
I tried the following but it does not give correct results.
i=1:n;c=prod(a(ind(i,1:non(i))).^b(i,1:non(i)),2);
Thank you in advance

Best Answer

Note that ind and b must be transposed for this to work:
>> a   = [4;2;1;3;1;4;4;0]; % must be column!
>> ind = [1,0;2,3;4,0;3,3;5,3].'; % transposed!

>> b   = [5,0;2,2;1,0;2,2;2,2].'; % transposed!
>> idx  = b~=0;
>> XC = ind(idx);
>> bC =   b(idx);
>> [~,idc] = find(idx);
>> out = accumarray(idc,a(XC).^bC,[],@prod)
out =
  1024
  4
  3
  1
  1
Related Question