# What are positive and negative circles in weighted digraph?

I am going through Warshall and Floyd algorithms and I read that Floyd's algorithm does not hold if a graph has negative circle. I have not been able to fully figure out what negative circle means. Therefore, I would like to know more about positive and negative circles.

A circle is a path in the graph ($v\to u_1 \to u_2 \to \cdots \to v$) starting from some node $v$, that goes back to node $v$, thus "closing a circle".