# Max step size

Maximum step size for variable-step solver

Model Configuration Pane: Solver

## Description

Specify the largest time step, in seconds, for the variable-step solver to take in simulation.

## Dependencies

To enable this parameter, set the solver Type to `Variable-step`.

## Settings

`auto` (default) | scalar

By default, the Max step size value is `auto`, which indicates that the solver determines the maximum step size to use in the simulation. The way the solver determines the maximum step size depends on the type of variable-step solver selected.

• When the Solver parameter value is `discrete (no continuous states)`, the solver uses the smallest sample time in the model as the maximum step size.

• When the Solver parameter value is something other than `discrete (no continuous states)`, the maximum step size is determined based on the specified Start time and Stop time.

• When the stop time is `inf` or is equal to the start time, the maximum step size is `0.2`.

• For all other stop time values, the maximum step size is chosen such that the simulation has at least 50 time hits.

`${h}_{\mathrm{max}}=\frac{{t}_{stop}-{t}_{start}}{50}$`

• When your model includes a Sine Wave block or a Signal Generator block, the maximum step size is determined based on the highest specified frequency in the model $Fre{q}_{\mathrm{max}}$. The software ensures that the maximum step size results in a sample rate larger than the Nyquist rate for all periodic signals in the model.

`${h}_{\mathrm{max}}=\mathrm{min}\left(\frac{{t}_{stop}-{t}_{start}}{50},\left(\frac{1}{3}\right)\left(\frac{1}{Fre{q}_{\mathrm{max}}}\right)\right)$`

Generally, the solver determines an appropriate maximum step size. Consider specifying the maximum step size when:

• You simulate the model over a large time span. For long time spans, the step size the solver chooses might be too large to find the solution.

• Your model contains periodic or nearly periodic behavior, and you know the period. Specify the maximum step size to a fraction of the period, such as `1`/`4`.

• You are concerned about the solver missing significant behavior when using the solver-determined maximum step size.

## Recommended Settings

The table summarizes recommended values for this parameter based on considerations related to code generation.

ApplicationSetting
DebuggingNo impact
TraceabilityNo impact
EfficiencyNo impact
Safety precautionNo impact

## Programmatic Use

 Parameter: `MaxStep` Type: string | character vector Value: numeric scalar Default: `'auto'`

## Version History

Introduced before R2006a