These are the nodal equations of a circuit having two nonreference node voltages, v1 and v, three conductance, and an independent current source ig. From our shortcut procedure for nodal equations we see that G1 and G2 are connected to first node, G2 is common to the two nodes, G2 and G3 are connected to the second node, and ig enters the first node. Since G1 and ig are not connected to the second node and G3 is not connected to the first node, these elements are connected to the reference node. Such a circuit is shown in Fig. 4.17 and is a dual of Fig. 4.16