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Choosing a Time Step

  Once a finite difference algorithm is chosen and implemented, one must determine a suitable time step, dt, for the simulation. A ``good'' time step is large enough that the system evolves rapidly, yet small enough that the finite difference algorithm is accurate. There is no inherently ``good'' time step--- rather, the size of an appropriate time step depends on the system being simulated. In this simulation, the user has three options for selecting a time step. These options, accessed by the mouse sequence Parameters Numerical are:

  1. Scale the time step by the period of the micromotion.
  2. Scale the time step by the Einstein period.
  3. Implement a user-specified time step.
The last of these options--- user-defined--- is exactly what one would expect: the user explicitly sets a time step, dt, and the program does not initiate any changes to dt. The first two choices, discussed below, implement various computer algorithms designed to find ``good'' time steps.



Wolfgang Christian
Fri May 12 10:36:01 EDT 1995