First of all, let me preface by saying that this question is not completly new but the original question hasn't been answered. More important, this is only basic question on understanding the proof itself.
So after some search in the site I found the following question : Bellman-Ford algorthm and negative cycle proof.
The guy is trying to understand how to prove that a cycle in parent pointer is necessarily a negative cycle.
My question is very basic and isn't duplicate, I just couldn't find anything in the document on the related question which answers my question.
What does it mean a cycle in the parent pointer? I mean I could a graph whereas the cycle in the parent pointer isn't a negative cycle... I don't understand why It must be a negative cycle.
See an example of a graph I have in mind :
Now suppose the first node we start with is (a) and suppose the we travling the edges in the following order: ab,bc,cd.
and here we goes, we have a cycle in the parent pointer, and as far as I understand that is (c) becuase it is the parent of (d) and yet the cycle isn't negative cycle.