# [[Optimization]]
# HDMR
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{{Image:FDTD57.png|thumb|250px|Figure 1: [[EM.Cube]]'s FDTD Simulation dialog.}}
Analysis is the simplest and most straightforward simulation mode of the [[FDTD Module]]. It runs the FDTD time marching loop once. At the end of the simulation, the time-domain field data are transformed into the frequency domain using a discrete Fourier transform (DFT). As a result, you can generate wideband frequency data from a single time-domain simulation run. The other simulation modes will be explained later in this manual.
To open the Simulation Run Dialog, click the '''Run''' [[Image:run_icon.png]] button of the '''Simulate Toolbar''' or select '''Menu > Simulate > Run...''' from the menu bar or use the keyboard shortcut '''Ctrl+R'''.
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[[Image:FDTD57.png]]
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Figure 1: [[EM.Cube]]'s FDTD Simulation dialog.
To start the FDTD simulation, click the '''Run''' button at the bottom of this dialog. Once the simulation starts, the "'''Output Window'''" pops up and reports messages during the different stages of the FDTD simulation. During the FDTD time marching loop, after every 10th time step, the output window updates the values of the time step, elapsed time, the engine performance in Mega-cells per seconds, and the value of the convergence ratio U<sub>n</sub>/U<sub>max</sub> in dB. An [[EM.Cube]] FDTD simulation is terminated when the ratio U<sub>n</sub>/U<sub>max</sub> falls below the specified power threshold or when the maximum number of time steps is reached. You can, however, terminate the FDTD engine earlier by clicking the '''Abort Simulation''' button.
[[Image:{{isoimg|FDTD66.png]]Â Figure 2: |[[FDTD Module]]'s output window.}}
===Waveforms & Discrete Fourier Transforms===