Writing M S-Functions (Writing S-Functions)

Writing S-Functions

S-Function Arguments

Simulink passes the following arguments to an S-function:

t
Current time

x
State vector

u
Input vector

flag
Integer value that indicates the task to be performed by the S-function

`t`	Current time
`x`	State vector
`u`	Input vector
`flag`	Integer value that indicates the task to be performed by the S-function

The following table describes the values that flag can assume and lists the corresponding S-function method for each value.

Table 2-1: Flag Argument
Flag
S-Function Routine
Description

0
mdlInitializeSizes
Defines basic S-Function block characteristics, including sample times, initial conditions of continuous and discrete states, and the sizes array.

1
mdlDerivatives
Calculates the derivatives of the continuous state variables.

2
mdlUpdate
Updates discrete states, sample times, and major time step requirements.

3
mdlOutputs
Calculates the outputs of the S-function.

4
mdlGetTimeOfNextVarHit
Calculates the time of the next hit in absolute time. This routine is used only when you specify a variable discrete-time sample time in mdlInitializeSizes.

9
mdlTerminate
Performs any necessary end-of-simulation tasks.

**Table 2-1: Flag Argument**
Flag	S-Function Routine	Description
0	`mdlInitializeSizes`	Defines basic S-Function block characteristics, including sample times, initial conditions of continuous and discrete states, and the `sizes` array.
1	`mdlDerivatives`	Calculates the derivatives of the continuous state variables.
2	`mdlUpdate`	Updates discrete states, sample times, and major time step requirements.
3	`mdlOutputs`	Calculates the outputs of the S-function.
4	`mdlGetTimeOfNextVarHit`	Calculates the time of the next hit in absolute time. This routine is used only when you specify a variable discrete-time sample time in `mdlInitializeSizes`.
9	`mdlTerminate`	Performs any necessary end-of-simulation tasks.

Writing M S-Functions S-Function Outputs