how to use vectorized language or any other methods to replace the following code, in order to make the computation faster

following are my current code:

if true
  % code
tic;
S = size(P,1);
Q2 = -permute(P,[2 3 1]);
for i = 1:S
  Q2(i,:,i) = Q2(i,:,i) + 1;
end
Q2 = reshape(Q2,S,[]);
toc
end

P is the transition probability matrix,

if true
  % code
P(:,:,1)=[3/4 1/4;3/4 1/4];
P(:,:,2)=[1/4 3/4;1/4 3/4];
end

My problem is that when the dimension of P is larger than 8000*8000*8,the current computation will be very slow.Is there anyone who know how to optimize the current code? Thank you in advance！

Answer 1

[jgg]

I think this should work. Replace your for loop with:

 i = [1:S]
 Q2(i,:,i) = Q2(i,:,i) + 1;

This works on the test case you posed, as far as I can tell, so I think it should work on your much bigger data. Let me know!

[Jason]

yes, it works, thank you very much !