### SIM-TDIS

#### Structure of Blocks

_FOR EACH SIMULATION_

```
    BEGIN OPTIONS
      [TIME_UNITS <time_units>]
      [START_DATE_TIME <start_date_time>]
      [ATS6 FILEIN <ats6_filename>]
    END OPTIONS
```
```
    BEGIN DIMENSIONS
      NPER <nper>
    END DIMENSIONS
```

_FOR ANY STRESS PERIOD_

```
    BEGIN PERIODDATA
      <perlen> <nstp> <tsmult>
      <perlen> <nstp> <tsmult>
      ...
    END PERIODDATA
```

#### Explanation of Variables

##### Block: OPTIONS

  * `time_units` is the time units of the simulation.  This is a text string that is used as a label within model output files.  Values for time_units may be "unknown",  "seconds", "minutes", "hours", "days", or "years".  The default time unit is "unknown".

  * `start_date_time` is the starting date and time of the simulation.  This is a text string that is used as a label within the simulation list file.  The value has no effect on the simulation.  The recommended format for the starting date and time is described at https://www.w3.org/TR/NOTE-datetime.

  * `ATS6` keyword to specify that record corresponds to an adaptive time step (ATS) input file.  The behavior of ATS and a description of the input file is provided separately.

  * `FILEIN` keyword to specify that an input filename is expected next.

  * `ats6_filename` defines an adaptive time step (ATS) input file defining ATS controls.  Records in the ATS file can be used to override the time step behavior for selected stress periods.

##### Block: DIMENSIONS

  * `nper` is the number of stress periods for the simulation.

##### Block: PERIODDATA

  * `perlen` is the length of a stress period.

  * `nstp` is the number of time steps in a stress period.

  * `tsmult` is the multiplier for the length of successive time steps. The length of a time step is calculated by multiplying the length of the previous time step by TSMULT. The length of the first time step, Delta t_1, is related to PERLEN, NSTP, and TSMULT by the relation Delta t_1= perlen frac{tsmult - 1}{tsmult<sup>nstp</sup>-1}.

#### Example Input File
```
    # Comment for this TDIS input file
    
    BEGIN OPTIONS
      TIME_UNITS DAYS
    END OPTIONS
    
    BEGIN DIMENSIONS
      NPER 2
    END DIMENSIONS
    
    BEGIN PERIODDATA
       365.00  1 1.0   Items: PERLEN NSTP TSMULT
       365.00 10 1.2   Items: PERLEN NSTP TSMULT
    END PERIODDATA
```