### 13. Running Multi-Tone AC Analysis

Each Multi-Tone AC Analysis involves two linked simulation runs:

1. A long transient simulation with the multi-tone injection source active. The simulation must run until the converter enters steady-state, and the natural response has settled out.
2. A "short" transient simulation which starts from the steady-state conditions found in the first simulation. This simulation extracts the AC response of the circuit, and the simulation time must be at least one period of the lowest injected frequency.

The interface between the two simulations is the SIMPLIS .INIT file, which saves the steady-state conditions to set the initial conditions for the second run.