Lumped impedance

impedance constructs a series multiport element from a constant or frequency-dependent impedance matrix. For $n$ pins, the ABCD representation of a series impedance $\mathbf{Z}$ is

\[\begin{bmatrix} \mathbf{A} & \mathbf{B} \\ \mathbf{C} & \mathbf{D} \end{bmatrix} = \begin{bmatrix} \mathbf{I} & \mathbf{Z} \\ \mathbf{0} & \mathbf{I} \end{bmatrix}.\]

A scalar z produces identical diagonal impedances. A vector with pins entries sets the diagonal independently, while a pins × pins matrix retains all diagonal and mutual terms. A callable z(s) provides a frequency-dependent matrix evaluated at the complex frequency supplied by the analysis kernel.

scalar = impedance(z = 5.0, pins = 1)
diagonal = impedance(z = [1.0, 2.0, 3.0], pins = 3)
coupled = impedance(z = [1.0 0.1; 0.1 2.0], pins = 2)
dynamic = impedance(z = s -> 0.1 + s * 2e-3, pins = 1)

The complete network admittance is assembled using modified nodal analysis [29]. See impedance for validation and current constructor details.