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/* Dispersive Materials */
If two or more material groups are defined in the Navigation Tree, only one of them can be active. By default, the last material defined is active. When you draw new objects, they are inserted under the active material node of the Navigation Tree, which is always listed in bold letters. Any material can be made active by right clicking on its name in the Navigation Tree and selecting the '''Activate''' item of the contextual menu.
[[Image:FDTD21(1).png|thumb|250px|Moving objects from one FDTD material group to another.]]
You can move one or more selected objects to any other material group. Right click on the highlighted selection and select '''Move To > FDTD >''' from the contextual menu. This opens another sub-menu with a list of all the available material groups already defined in your [[FDTD Module]] project. Select the desired material node, and all the selected objects will move to that material group. The objects can be selected either in the project workspace, or their names can be selected from the Navigation Tree. In the case of a multiple selection from the Navigation Tree using the keyboard's '''Shift Key''' or '''Ctrl Key''', make sure that you continue to hold the keyboard's '''Shift Key''' or '''Ctrl Key''' down while selecting the "Destination" material group's name from the contextual menu.
In a similar way, you can move one or more objects from an FDTD material group to one of [[EM.Cube]]'s other modules. In this case, the sub-[[menus]] of the '''Move To >''' item of the contextual menu will indicate all the [[EM.Cube]] modules that have valid groups for transfer of the selected objects. You can also move one or more objects from [[EM.Cube]]'s other modules to a material group in the [[FDTD Module]]. This is especially useful when importing structure from external model files. Keep in mind that in [[EM.Cube]] you can import external objects only to '''[[CubeCAD]]'''.
==Computational Domain & FDTD Mesh Generation==
The serial CPU solver is [[EM.Cube]]'s basic FDTD kernel that run the time marching loop on a single central processing unit (CPU) of your computer. The default option is the multi-core CPU solver. This is a highly parallelized version of the FDTD kernel based on the Open-MP framework. It takes full advantage of a multi-core, multi-CPU architecture, if your computer does have one. The GPU solver is a hardware-accelerated FDTD kernel optimized for CUDA-enabled graphical processing unit (GPU) cards. If your computer has a fast NVIDIA GPU card with enough onboard RAM, the GPU kernel can speed up your FDTD simulations up to 50 times or more over the single CPU solver.
For structures excited with a plane wave source, there are two standard FDTD formulations: '''Scattered Field '''(SF) formulation and '''Total Field - Scattered Field''' (TF-SF) formulation. [[EM.Cube]]'s [[FDTD Module|FDTD module]] offers both formulations. The TF-SF solver is the default choice and is typically much faster than the SF solver for most problems. In two cases, when the structure has periodic boundary conditions or infinite CPML boundary conditions (zero domain offsets), only the SF solver is available. The other sections of the FDTD Simulation Engine Settings dialog will be described next in the context of [[Waveforms and Discrete Fourier Transforms]].
===Running A Wideband FDTD Simulation===
