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MATLAB S-Function Basics

Principles of S-function implementation

An S-function is a computer language description of a Simulink® block written in MATLAB®, C, C++, or Fortran. C, C++, and Fortran S-functions are compiled as MEX files using the mex utility. See Build C MEX Function. As with other MEX files, S-functions are dynamically linked subroutines that the MATLAB execution engine can automatically load and execute. If you have Simulink Coder™, you can generate code for Level-2 MATLAB S-functions if they are inlined. See Inlining S-Functions (Simulink Coder) for more information.

You can implement S-functions in these ways:

  • Level-2 MATLAB S-Function — Provides access to a more extensive set of the S-function API and supports code generation.

  • C MEX S-Function — Enables you to implement your algorithm as a C MEX S-function or write a wrapper S-function to call existing C, C++, or Fortran code.

  • The S-Function Builder — Provides a graphical user interface that is used to generate new S-functions or incorporate existing C or C++ code without interacting with the S-function API.

  • The Legacy Code Tool — Provides a set of MATLAB commands that helps you create an S-function to incorporate existing C or C++ code.