Transport problem by the minimum element method. How to make an iteration of improving the result?

Question

Mathematics

I solve the transport problem by the method of the minimum element, then I bring it to the optimal form by the method of potentials. Who does not know what it is, google.ru will help.
The problem is, I can't find the loop. I will explain - after finding the potentials, you need to check according to the condition, there are in the picture, if they are not fulfilled, then you need to improve the plan, it improves by finding the cycle where the tariffs are added and decreased.
How can it be found?