[[File:PO27.png|thumb|400px|EM.Illumina's Simulation Run dialog.]]
[[File:PO28.png|thumb|350px|EM.Illumina's Simulation Engine Settings dialog.]]
Once you have set up your structure in EM.Illumina, have defined sources and observables and have examined the quality of the structure's mesh, you are ready to run a Physical Optics simulation. EM.Illumina offers five simulation modes (click on each type to learn more about it):
* '''[[#Running a Single{| class="wikitable"|-! scope="col"| Simulation Mode! scope="col"| Usage! scope="col"| Number of Engine Runs! scope="col"| Frequency PO Analysis ! scope="col"| Restrictions|-| style="width:120px;" | Single-Frequency Analysis]]'''* '''[[Parametric_Modeling,_Sweep_%26_Optimization#Running_Frequency_Sweep_Simulations_in_EM.Cube | style="width:270px;" | Simulates the physical structure "As Is"| style="width:80px;" | Single run| style="width:250px;" | Runs at the center frequency fc| style="width:80px;" | None|-| style="width:120px;" | Frequency Sweep]]''' | style="width:270px;" | Varies the operating frequency of the PO solver * '''[[Parametric_Modeling,_Sweep_%26_Optimization#Running_Parametric_Sweep_Simulations_in_EM.Cube | style="width:80px;" | Multiple runs | style="width:250px;" | Runs at a specified set of frequency samples| style="width:80px;" | None|-| style="width:120px;" | Parametric Sweep]]'''* '''[[Parametric_Modeling,_Sweep_%26_Optimization#Optimization | style="width:270px;" | Varies the value(s) of one or more project variables| style="width:80px;" | Multiple runs| style="width:250px;" | Runs at the center frequency fc| style="width:80px;" | None|-| style="width:120px;" | Optimization]]'''* '''[[Building_Reusable_Models#Running_an_HDMR_Sweep | style="width:270px;" | Optimizes the value(s) of one or more project variables to achieve a design goal | style="width:80px;" | Multiple runs | style="width:250px;" | Runs at the center frequency fc| style="width:80px;" | None|-| style="width:120px;" | HDMR Sweep]]'''| style="width:270px;" | Varies the value(s) of one or more project variables to generate a compact model| style="width:80px;" | Multiple runs | style="width:250px;" | Runs at the center frequency fc| style="width:80px;" | None|}
You can set the simulation mode from EM.Illumina's "Simulation Run Dialog". A single-frequency analysis is a single-run simulation. All the other simulation modes in the above list are considered multi-run simulations. If you run a simulation without having defined any observables, no data will be generated at the end of the simulation. In multi-run simulation modes, certain [[parameters]] are varied and a collection of simulation data files are generated. At the end of a sweep simulation, you can graph the simulation results in EM.Grid or you can animate the 3D simulation data from the navigation tree.