## Fixed-step size (fundamental sample time)

### Description

Specify the step size used by the selected fixed-step solver.

Category: Solver

### Settings

Default: `auto`

• Entering `auto` (the default) in this field causes Simulink® to choose the step size.

• If the model specifies one or more periodic sample times, Simulink chooses a step size equal to the greatest common divisor of the specified sample times. This step size, known as the fundamental sample time of the model, ensures that the solver will take a step at every sample time defined by the model.

• If the model does not define any periodic sample times, Simulink chooses a step size that divides the total simulation time into 50 equal steps.

• If the model specifies no periodic rates and the stop time is `Inf`, Simulink uses 0.2 as the step size. Otherwise, it sets the fixed-step size to

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

• For Sine and Signal Generator source blocks, if the stop time is `Inf`, Simulink calculates the step size using this heuristic:${h}_{\mathrm{max}}=\mathrm{min}\left(\left(0.2\right),\left(\frac{1}{3}\right)\left(\frac{1}{Fre{q}_{\mathrm{max}}}\right)\right)$Otherwise, the step size is:

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

where $Fre{q}_{\mathrm{max}}$ is the maximum frequency (Hz) of these blocks in the model.

### Dependencies

This parameter is enabled only if the Periodic sample time constraint is set to `Unconstrained`.

### Command-Line Information

 Parameter: `FixedStep` Type: character vector Value: any valid value Default: `'auto'`

### Recommended Settings

ApplicationSetting
DebuggingNo impact
TraceabilityNo impact
EfficiencyNo impact
Safety precautionNo impact