Writing S-Functions Previous page   Next Page

S-Function Examples

Simulink comes with a library of S-function examples.

To run an example:

  1. Enter sfundemos at the MATLAB command line.
  1. MATLAB displays the S-function demo library

    Each block represents a category of S-function examples.

  1. Click a category to display the examples that it includes.

  2. Click a block to open and run the example that it represents.

It might be helpful to examine some sample S-functions as you read the next chapters. Code for the examples is stored in these subdirectories under the MATLAB root directory:

M-files
toolbox/simulink/blocks
C, C++, and Fortran
simulink/src
Ada
simulink/ada/examples

M-File S-Function Examples

The simulink/blocks directory contains many M-file S-functions. Consider starting off by looking at these files.

Filename
Description
csfunc.m
Define a continuous system in state-space format.
dsfunc.m
Define a discrete system in state-space format.
vsfunc.m
Illustrates how to create a variable sample time block. This block implements a variable step delay in which the first input is delayed by an amount of time determined by the second input.
mixed.m
Implement a hybrid system consisting of a continuous integrator in series with a unit delay.
vdpm.m
Implement the Van der Pol equation (similar to the demo model, vdp).
simom.m
Example state-space M-file S-function with internal A, B, C, and D matrices. This S-function implements
dx/at = Ax + By
y = Cx + Du

where x is the state vector, u is the input vector, and y is the output vector. The A, B, C, and D matrices are embedded in the M-file.
simom2.m
Example state-space M-file S-function with external A, B, C, and D matrices. The state-space structure is the same as in simom.m, but the A, B, C, and D matrices are provided externally as parameters to this file.
limintm.m
Implement a continuous limited integrator where the output is bounded by lower and upper bounds and includes initial conditions.
sfun_varargm.m

Example M-file S-function showing how to use the MATLAB vararg facility.

vlimintm.m

Example of a continuous limited integrator S-function. This illustrates how to use the size entry of -1 to build an S-function that can accommodate a dynamic input/state width.

vdlimintm.m

Example of a discrete limited integrator S-function. This example is identical to vlimint.m, except that the limited integrator is discrete.

C S-Function Examples

The simulink/src directory also contains examples of C MEX S-functions, many of which have an M-file S-function counterpart. These C MEX S-functions are listed in this table.

Filename
Description
barplot.c

Access simulink signals without using the standard block inputs.

csfunc.c

Example C MEX S-function for defining a continuous system.

dlimint.c
Implement a discrete-time limited integrator.
dsfunc.c
Example C MEX S-function for defining a discrete system.
fcncallgen.c
Execute function-call subsystems n times at the designated rate (sample time).
limintc.c
Implement a limited integrator.
mixedm.c
Implement a hybrid dynamic system consisting of a continuous integrator (1/s) in series with a unit delay (1/z).
mixedmex.c
Implement a hybrid dynamic system with a single output and two inputs.
quantize.c

Example MEX-file for a vectorized quantizer block. Quantizes the input into steps as specified by the quantization interval parameter, q.

resetint.c
A reset integrator.
sdotproduct
Compute dot product (multiply-accumulate) of two real or complex vectors.
sftable2.c
Two-dimensional table lookup in S-function form.
sfun_atol.c
Set different absolute tolerances for each continuous state.
sfun_bitop.c
Perform the bitwise operations AND, OR, XOR, left shift, right shift, and one's complement on uint8, uint16, and uint32 inputs.
sfun_cplx.c
Complex signal add with one input port and one parameter.
sfun_directlook.c
Direct 1-D lookup.
sfun_dtype_io.c
Example of the use of Simulink data types for inputs and outputs.
sfun_dtype_param.c
Example of the use of Simulink data types for parameters.
sfun_dynsize.c
Simple example of how to size outputs of an S-function dynamically.
sfun_errhdl.c
Simple example of how to check parameters using the mdlCheckParams S-function routine.
sfun_fcncall.c
Example of an S-function that is configured to execute function-call subsystems on the first and third output elements.
sfun_frmad.c
Frame-based A/D converter.
sfun_frmda.c
Frame-based D/A converter.
sfun_frmdft.c
Multichannel frame-based Discrete-Fourier transformation (and its inverse).
sfun_frmunbuff.c
Frame-based unbuffer block.
sfun_multiport.c

S-function that has multiple input and output ports.

sfun_manswitch.c

Manual switch.

sfun_matadd.c

Matrix add with one input port, one output port, and one parameter.

sfun_multirate.c

Demonstrate how to specify port-based sample times.

sfun_psbbreaker.c

Implement the logic for the breaker block in the Power System Blockset.

sfun_psbcontc.c

Continuous implementation of state-space system.

sfun_psbdiscc.c

Discrete implementation of state-space system.

sfun_runtime1.c

Run-time parameter example.

sfun_runtime2.c

Run-time parameter example.

sfun_zc.c
Demonstrate use of nonsampled zero crossings to implement abs(u). This S-function is designed to be used with a variable-step solver.
sfun_zc_sat.c
Saturation example that uses zero crossings.
sfunmem.c
A one-integration-step delay and hold memory function.
simomex.c

Implements a single-output, two-input state-space dynamic system described by these state-space equations

  • dx/dt = Ax + Bu
    y = Cx + Du
    

where x is the state vector, u is vector of inputs, and y is the vector of outputs.

smatrxcat.c

Matrix concatenation.

sreshape.c

Reshape the input signal.

stspace.c

Implement a set of state-space equations. You can turn this into a new block by using the S-Function block and mask facility. This example MEX-file performs the same function as the built-in State-Space block. This is an example of a MEX-file where the number of inputs, outputs, and states is dependent on the parameters passed in from the workspace. Use this as a template for other MEX-file systems.

stvctf.c

Implement a continuous-time transfer function whose transfer function polynomials are passed in via the input vector. This is useful for continuous time adaptive control applications.

stvdct.f

Implement a discrete-time transfer function whose transfer function polynomials are passed in via the input vector. This is useful for discrete-time adaptive control applications.

stvmgain.c

Time-varying matrix gain.

table3.c

3-D lookup table.

timestwo.c

Basic C MEX S-function that doubles its input.

vdlmint.c
Implement a discrete-time vectorized limited integrator.
vdpmex.c
Implement the Van der Pol equation.
vlimint.c

Implement a vectorized limited integrator.

vsfunc.c

Illustrate how to create a variable sample time block in Simulink. This block implements a variable-step delay in which the first input is delayed by an amount of time determined by the second input.

Fortran S-Function Examples

Filename
Description
sfun_timestwo_for.for
Sample Level 1 Fortran representation of a C timestwo S-function.
sfun_atmos.c
Calculation of the 1976 standard atmosphere to 86 km.
vdpmexf.for
Van der Pol system.
The following table lists sample Fortran S-functions.

C++ S-Function Examples

Filename
Description
sfun_counter_cpp.cpp
Store a C++ object in the pointers vector PWork.
The following table lists sample C++ S-functions.

Ada S-Function Examples

The simulink/ada/examples directory contains the following examples of S-functions implemented in Ada.

Directory Name
Description
matrix_gain
Implement a Matrix Gain block.
multi_port
Multiport block.
simple_lookup
Lookup table. Illustrates use of a wrapper S-function that wraps stand-alone Ada code (i.e., Ada packages and procedures) both for use with Simulink as an S-function and directly with Ada code generated using the RTW Ada Coder.
times_two
Output twice its input.


Previous page  Setting Sample Times and Offsets Writing M S-Functions Next page