The Concept of Time in Simulations

In SIMION, there are a couple different concepts of time. First, there is the time (t) that occurs experimentally in the instrument you are designing, such as a one microsecond time for particles at a cathode to reach an anode. Second, there is the time (T) at which that system is simulated on the CPU. T may bear little resemblance to t in terms of their durations and chronology. For example, just because one ray may emit from a cathode before another ray does not necessarily mean we must calculate the trajectories of those rays in that order, and the time required to make that calculation could be orders of magnitude shorter of longer than the actual experiment. Third, there is the time in which the results of the simulation are visualized on the screen for the user, which in SIMION is often the same as T because calculation and visualization are normally done concurrently, but these could be different if you replayed the trajectories with the flying as Dots option or captured it as a movie and replayed it at a different speed. The visualization speed is typically intentionally much slower than t since microsecond timeframes are too fast for human perception.

Further breaking down simulation time: Since your CPU may be doing other tasks at the same time it is calculating your simulation (e.g. web browsing or waiting for disk and memory I/O) and you may even temporarily pause the simulation (Pause checkboxes on Particles tab), we may also consider just the portion of T in which the CPU is actively doing your calculation. The term wall-clock time is used to refer to the total time T (see Wikipedia:Wall_clock_time), and CPU time may refer to just the portion. There may also be multiple CPUs or cores involved.


This page is abridged from the full SIMION 8.1.1 "Supplemental Documentation" (Help file). The following additional sections can be found in the full version of this page accessible via the "Help > Supplemental Documentation" menu in SIMION 8.1.1:
  • Relationship of T v.s. t
  • User Programming Cautions
  • Units
  • Lua

Time-Dependent Fields

For information on time-dependent fields, including RF fields and varying electrode voltages, see Time-Dependent Field.