Function Definition

Defining and calling functions for code generation

There are special considerations when you create MATLAB^® functions that are intended for code generation. These include certain restrictions when you use varargin and varargout, recursive functions, anonymous functions, and nested functions. To generate code for MATLAB recursive functions, the code generator uses either compile-time recursion or run-time recursion. To produce efficient C/C++ code, the code generator sometimes creates multiple versions of a function, referred to as function specializations. In certain cases, you can prevent the code generator from creating function specializations by using coder.ignoreSize and coder.ignoreConst. While generating a MEX function, you can bypass code generation for a specific function in your MATLAB code and instead use the MATLAB engine to execute the call. To do this, use the coder.extrinsic construct.

Functions

`coder.extrinsic`	Declare function as extrinsic and execute it in MATLAB
`coder.ignoreConst`	Prevent use of constant value of expression for function specializations
`coder.ignoreSize`	Prevent code generator from creating function specializations for constant-size expressions
`coder.mustBeComplex`	Validate that value lies on the complex plane (Since R2023b)
`coder.mustBeConst`	Validate that value is a compile-time constant (Since R2023b)
`coder.noImplicitExpansionInFunction`	Disable implicit expansion within the specified function in the generated code (Since R2021b)
`coder.sameSizeBinaryOp`	Apply element-wise binary operations without implicit expansion (Since R2021b)
`coder.specifyAsGPU`	Specify that value is a GPU input to an entry-point function for GPU code generation (Since R2023b)

Topics

Compilation Directive %#codegen
Indicate that a MATLAB function is intended for code generation.
Generate Code With Implicit Expansion Enabled
The code generator introduces modifications in the generated code to accomplish implicit expansion.
Optimize Implicit Expansion in Generated Code
Implicit expansion in the generated code is enabled by default.
Code Generation for Variable Length Argument Lists
Generate code for varargin and varargout.
Generate Code for arguments Block That Validates Input and Output Arguments
Generate code for MATLAB code that constrains class, size, and other aspects of function input and output values.
Code Generation for Recursive Functions
Use recursive functions in MATLAB code that is intended for code generation.
Force Code Generator to Use Run-Time Recursion
Rewrite your MATLAB code so that the code generator uses run-time recursion instead of compile-time recursion.
Code Generation for Anonymous Functions
Use anonymous functions in MATLAB code intended for code generation.
Code Generation for Nested Functions
Use nested functions in MATLAB code intended for code generation.
Resolution of Function Calls for Code Generation
The code generator uses precedence rules to resolve function calls.
Resolution of File Types on Code Generation Path
The code generator uses precedence rules to resolve file types.
Use MATLAB Engine to Execute a Function Call in Generated Code
If a function is not supported for code generation, declare it as extrinsic to execute in MATLAB.

Troubleshooting

Nonconstant Index into varargin or varargout in a for-Loop

Force loop unrolling when the code generator cannot determine the value of the index into varargin or varargout.

Avoid Duplicate Functions in Generated Code

Reduce the occurrence of duplicate functions in the generated code.

Output Variable Must Be Assigned Before Run-Time Recursive Call

Troubleshoot output variable assignment for run-time recursion.

Compile-Time Recursion Limit Reached

Troubleshoot compile-time recursion limit error.

Resolve Error: Size Mismatches

Troubleshoot size mismatch errors that occur during code generation.

Resolve Issue: coder.inline("never") and coder.nonInlineCall Do Not Prevent Function Inlining

Troubleshoot instances of coder.inline('never') not preventing inlining.

Resolve Issue: Variables Must Be Fully Defined Before Use

Troubleshoot code generation errors when variables, including structure fields and class properties, are not defined before use.