# 4. Automatic Time Step Selector

For performance reasons, it is sometimes desired to run at the highest possible time step in explicit dynamics. The `NODE BASED TIME STEP` and the `LANCZOS TIME STEP` have proven to yield a higher time step than the default element time step for most problems. However, because these routines take significantly more time to calculate, sometimes the performance benefits are unseen. The automatic time step selector attempts to weigh the performance benefits of each time step calculation. The time steps are compared every hundred steps, and the one proving most beneficial is used for the proceeding hundred steps.

Currently, only the node based time step and the element time step are compared. Because the node based time step takes longer to calculate than the element based time step (as noted above), a scale factor is used when comparing the two. To run with the automatic time step selector, the following must be included in the input file:

In the `BEGIN PARAMETERS FOR PRESTO REGION` block, the following line must be included:

    BEGIN PARAMETERS FOR PRESTO REGION <string>presto_region
      TIME STEP SELECTOR = AUTO
    END PARAMETERS FOR PRESTO REGION <string>presto_region

Additionally, the node based time step syntax must also be included in the input file:

    BEGIN NODE BASED TIME STEP PARAMETERS <string>name
    END NODE BASED TIME STEP PARAMETERS <string>name