set the row of this vertex in the Hessian

Resize the vertex state. In this case, we want to preserve as much of the state as we can. Therefore, we use conservativeResize and pad with zeros at

Resize the vertex state. In this case, we simply trash whatever was there before.

true => this node should be considered fixed during the optimization

sets the id of the node in the graph be sure that the graph keeps consistent after changing the id

sets the level of the edge

true => this node should be marginalized out during the optimization