Writing S-Functions

S-Function Arguments

Simulink passes the following arguments to an S-function:

• t, the current time
• x, the state vector
• u, the input vector
• flag, an 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.

Writing M S-Functions

S-Function Outputs