Writing S-Functions

Initialization Pane

The Initialization pane allows you to specify basic features of the S-function, such as the width of its input and output ports and its sample time.

The S-Function Builder uses the information that you enter on this pane to generate the S-function's mdlInitializeSizes callback method. Simulink invokes this method during the model initialization phase of the simulation to obtain basic information about the S-function. (See How Simulink Interacts with C S-Functions for more information on the model initialization phase.)

The Initialization pane contains the following fields.

Number of discrete states

Number of discrete states that the S-function has.

Discrete states IC

Initial conditions of the S-function's discrete states. You can enter the values as a comma-separated list or as a vector (e.g., [0 1 2]). The number of initial conditions must equal the number of discrete states.

Number of continuous states

Number of continuous states that the S-function has.

Continuous states IC

Initial conditions of the S-function's continuous states. You can enter the values as a comma-separated list or as a vector (e.g., [0 1 2]). The number of initial conditions must equal the number of continuous states.

Sample mode

Sample mode of the S-function. The sample mode determines the length of the interval between the times when the S-function updates its output. You can select one of the following options:

• Inherited

• The S-function inherits its sample time from the block connected to its input port.

• Continuous

• The block updates its outputs at each simulation step.

• Discrete

• The S-function updates its outputs at the rate specified in the Discrete sample time value field of the S-Function Builder dialog box.

Sample time value

Interval between updates of the S-function's outputs. This field is enabled only if you have selected Discrete as the S-function's Sample time.   

Port/Parameter Pane

Data Properties Pane

© 1994-2005 The MathWorks, Inc.