# Vectorize nested for loop with matrix indexing

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Divye Kalra on 8 Jan 2022
Commented: Divye Kalra on 8 Jan 2022
Hello everyone, the code shown below works as intended. It's just that it takes quite a bit of time to execute.
Note : T is a 512x3 array of doubles, Z1 is a 512x512 array of doubles and Z1_encrypt = Z1 OR T
Z1_encrypt = [];
Z2_encrypt = [];
Z3_encrypt = [];
for i = 1:1:512
disp(i)
for j = 1:1:512
Z1_encrypt = [Z1_encrypt bitor(Z1(j,i),T(j,1),'uint64')];
Z2_encrypt = [Z2_encrypt bitor(Z2(j,i),T(j,2),'uint64')];
Z3_encrypt = [Z3_encrypt bitor(Z3(j,i),T(j,3),'uint64')];
end
end
I was looking into vectorization of code to speed it up and went over quite a few examples. One very similar example can be found here, but it was of not much help to me.
It would be great if someone could help me out here.

Chunru on 8 Jan 2022
% The following code is slow, because the array size is growing. Memory
% allocation will slow down the program
% Z1_encrypt = [];
% Z2_encrypt = [];
% Z3_encrypt = [];
% for i = 1:1:512
% disp(i)
% for j = 1:1:512
% Z1_encrypt = [Z1_encrypt bitor(Z1(j,i),T(j,1),'uint64')];
% Z2_encrypt = [Z2_encrypt bitor(Z2(j,i),T(j,2),'uint64')];
% Z3_encrypt = [Z3_encrypt bitor(Z3(j,i),T(j,3),'uint64')];
% end
% end
% ry the following for speed
Z1_encrypt = bitor(Z1,T(:,1),'uint64');
Z2_encrypt = bitor(Z1,T(:,2),'uint64');
Z3_encrypt = bitor(Z1,T(:,3),'uint64');
Divye Kalra on 8 Jan 2022
This worked, thanks!