Use the Time Discrete Solver () to find the solution to time-dependent problems (dynamic or unsteady problems) that have already been discretized in time using, for example, the prev operator or the bdf operator. This solver is automatically used when a Time Discrete study is added to the model.

See About the Time Discrete Solver for background information.

Use the Defined by study step list to specify if the settings are synchronized with the corresponding study step. If you select User defined (to override the settings defined in the corresponding study node), you can specify the Time unit, Output times, and Relative tolerance settings.

Use the Time unit list to choose a time unit that is suitable for the time span of the simulation. The default time unit is inherited from the corresponding setting in the study step.

Use the Output times field to enter a vector of times that define the simulation’s time span.

The time step is specified in the Time step field. Valid entries are a scalar, a vector of times, or an expression containing global expression variables.

Discretizing time derivatives using the prev operator or the bdf operator requires the solution at previous discrete times. How many previous time steps should be stored is specified in the Number of time discrete levels field. If you, for example, use the first-order bdf operator (bdf(u,1)), the solution at one previous time step is required. Using the second-order bdf operator (bdf(u,2)) requires the solution at two previous time steps. The default value is 2.

From the Times to store list, choose one of the following options:

Use the Relative tolerance field to enter a positive number. This number controls how accurately the nonlinear system of equations is solved in each time step. In general, the desired relative error in the solution should be entered here.

Use the Global method list to select how the specified absolute tolerance is to be interpreted for the variables that use the global method (by default, all variables use the global method). Select:

Select a Tolerance method to specify how to enter and compute the absolute tolerance. Select:

To specify the absolute tolerance individually for a variable, select the variable from the Variables list and modify the corresponding tolerance with the Method list. Select:

If you select Scaled or Unscaled, additional fields appear. Use the Tolerance field to modify the absolute tolerance for the selected variable.

See Results While Solving in Common Study Step Settings for these settings.

Use the Times to store list to control at what times the solver stores a solution. Select:

When Specified times is selected, the solution to output is computed through interpolation. Therefore, the solution at previous time steps is not computed, which means that expressions with the prev and bdf operators cannot be used in analysis. Such expressions can only be used in analysis when you have selected Steps taken by solver.

In this section you can define constants that can be used as temporary constants in the solver. You can use the constants in the model or to define values for internal solver parameters. These constants overrule any previous definition (for example, from Global Definitions). The constant values are expressions and can, for example, include the range() operator, units, and global expressions. The constant name can be a new or an existing global parameter. The constant is temporary in the sense that it is only defined during the solver run. You cannot override parameters used in the following parts of the model:

Click the Add button () to add a constant and then define its name in the Constant name column and its value (a numerical value or parameter expression) in the Constant value column. By default, any defined parameters are first added as the constant names, but you can change the names to define other constants. Click Delete () to remove the selected constant from the list.

This section, which is initially empty, contains a log from the time stepping. Select the Keep warnings in stored log check box as needed.