graph signals

Graph signals are data that exist on a graph $G$. Data are represented as vectors $x\in {\mathbb{R}}^n$ where $x_i$ is the signal value at node $i$. This is often implicit, but sometimes we will use the notation $(G,x)$.

There are two types of signals:

• fixed node properties or features are information associated with nodes
  • ex. Nodes belong to group A or group B
• graph signals (which often implies variability) can be interpreted as variables on the nodes of the graph
  • ex. traffic counts on the roads of minnesota