User-Defined Functions

R2026b

Blocks that extend Simulink functionality with custom algorithms, such as MATLAB Function, C Function, and S-Function

Use blocks from the User-Defined Functions library to extend Simulink^® modeling functionality by creating new types of blocks. You can implement block algorithms using MATLAB^®, C/C++, and Fortran^® code. Use these blocks when built-in blocks do not provide the specific computation or system behavior you need.

To add blocks from this library to your model, see Add Blocks to Models.

Blocks

	C Caller	Integrate C code in Simulink
	C Function	Integrate and call external C/C++ code from a Simulink model
	Fcn	Apply specified expression to input
	Function Caller	Call a Simulink function
	Initialize Function	Execute subsystem on model initialize event
	Interpreted MATLAB Function	(To be removed) Apply MATLAB function or expression to input
	Level-2 MATLAB S-Function	Use Level-2 MATLAB S-function in model
	MATLAB Function	Include MATLAB code in Simulink models
	MATLAB System	Include System object in model
	Python Code	Integrate native Python code into a Simulink model (Since R2025a)
	Reinitialize Function	Execute subsystem on model or subsystem reinitialize event (Since R2022a)
	Reset Function	Execute subsystem on model reset event
	S-Function	Include S-function in model
	S-Function Builder	Integrate C or C++ code to create S-functions
	Simulink Function	Define a function using Simulink blocks
	Terminate Function	Execute subsystem on model terminate event

Tools

Library Browser

Find and add blocks to model

Topics

Add Blocks to Models
Use the Library Browser and quick insert menu to insert blocks.

Related Information

Interactive Model Editing
Programmatic Model Editing

Featured Examples

Call Legacy Lookup Table Functions Using C Function Block

Use the C Function block to call legacy C functions that implement N-dimensional table lookups.

Open Script

Modify States of a C Function Block Using Persistent Symbols

Define an initial persistent value to cache in the block.

Open Model

Call C++ Class Methods Using C-Style Wrapper Function from C Function Block

Use the C Function block to call C++ class methods using a C-style wrapper function.

Open Model

Call C++ Class Methods Directly from a C Function Block

Call C++ Class Methods Directly From a C Function Block.

Open Script

Common Uses of the Initialize Function Block

Use the Initialize Function block to perform these common initialization actions.

Open Live Script

Working with the Reinitialize Function Block

Use a Reinitialize Function block to reset the initial condition of a Discrete-Time Integrator block for every function-call event received by a subsystem. In this example, the Reinitialize Function block is inside a subsystem, and the subsystem receives a function-call event at every five simulation time steps.

Open Live Script

Initialize, Reset, and Terminate State of Simulink Block

Use the Initialize Function, Reset Function, and Terminate Function blocks to respond to events in a Simulink model.

Open Model